FIRST SMOS Workshop
BARCELONA
September 8-10 1999
Workshop report
A General presentation
The first SMOS workshop took place in Barcelona on September 8-10 1999 at the Universitat
Politècnica de Catalunya. Over sixty attendees were present (see annex 1). The purposes of the
workshop were as follows:
1) Allow everyone to be updated on the current situation of the SMOS programme and on all the
relevant scientific activities since the proposal write up.
2) To review the mission objectives and requirements and make sure that the proposal is still
fully relevant before ESA initiates the Phase A studies. For this the idea was to assess the new state
of the art on the science point of view, what are the current plans of the different groups which could
be of interest to the SMOS investigations including the already started actions. These considerations
being useful to start addressing the ESAC review issues.
3) To have a first go at identifying the necessary scientific studies, algorithm developments and
related campaigns so as to give the SAG a starting point. This information could also be useful to
start initiating the discussion on the simulator and the necessary ground and aircraft sensors.
Consequently, the goals of the workshop were to:

Get the community informed on the status, get a clear idea of the science issues to be
addressed together with possible ways to solve them (campaigns, algorithms, ground instruments,
potential groups and priorities),

Prepare a starting point for the SAG,

Get a consensus on the mission objectives and requirements,

Initiate the simulator discussions
For this, the workshop was separated in three phases,

a set of plenary sessions (general information and update),

splinter sessions,

and finally a plenary session to confront the results of the splinter groups.
The agenda is given in annex 2
Acknowledgements are due to Jordi Font and the UPC team who achieved an excellent
organisation, and the chairmen of splinter for moderating the discussions and making available
quickly the summaries.
B First plenary session
The first half-day was devoted to plenary presentations and was an opportunity to update
everybody on the current situation. After a summary of the temporal evolution of the SMOS
proposal, Chris Readings gave an overview of the current plans at ESA and how SMOS fitted in it
1
with particular attention to the Earth Explorer Programme. Following this presentation, both CDTI
and CNES exposed their plans and interest and how the SMOS project fitted into it.
So as to give a more general overview, the outcome of two recent workshops on Sea Surface
Salinity (SSIWG Workshop, see http://www.esr.org/lagerloef/ssiwg/ssiwgrep1.v2.html) and on the
NASA Soil Moisture Mission document (see http://maximus.ce.washington.edu/~tempcm/Post2002/
smm3.html) where presented by respectively Gary Lagerloef and Tom Jackson.
The day ended with the presentation of the UPC simulator. It is very clear that we will need a
simulator to fine-tune the mission. Work performed at the UPC, OMP and IPSL is a good starting
point and should be pursued further.
C Splinter sessions
The second day was devoted to gathering data for reaching the workshop goals. For this we
separated into 4 groups. Three groups devoted their efforts to Ocean, Land and Image reconstruction.
During the second half of the day a fourth group convened to address the campaign issues in view of
what had been discussed in the other groups in the morning. It can also be stated that the Cryosphere
group, being to small merged with the land group but Martti Hallikainen prepared a report off line by
contacting directly various experts after the workshop.
The splinters were to address the following matters:
- Do they endorse the SMOS mission objectives and requirements
- Identify the scientific issues and prioritise them
- Establish a potential list of actions to be taken
- Campaigns and instruments
- Algorithm development
- Cal/Val
- Identify existing data sets
- Identify specific Studies
- Establish a summary of the recommendations
The outcome of the splinter sessions is given below. Since this is a working document, no
particular effort has been devoted to editing the summaries and dealing with redundancies.
C.1 Land Group Report
Chair Paolo Ferrazzoli, rapporteur Jean Pierre Wigneron
C1.1
ON GOING INVESTIGATIONS
C1.1.1 Retrieval of physical parameters from multi-angular dual-polarisation
measurements
Several studies demonstrated the possibility to retrieve simultaneously both soil moisture and
vegetation optical depth from multi-angular L-band radiometric data, using ground measurements of
TB and simulations.
For applications from spaceborne observations, the possibility to retrieve vegetation effects
concurrently with soil moisture is a result of key importance (Kerr et al., 1999):

There is no need of ancillary vegetation data to estimate the vegetation attenuation  from WC
and b (= b . WC). The 'simultaneous retrieval of (wS, )' simplifies considerably the retrieval process
since: (1) usually, the vegetation water content WC was roughly estimated from ancillary optical
remote sensing data and it is not easy to estimate this variable at large spatial scale; (2) the b
parameter was found to depend on canopy type (Jackson and Schmugge, 1991) and on the vegetation
2
moisture content (Le Vine and Karam, 1996, Wigneron et al., 1996).

The retrieved vegetation optical depth  may be a very useful product for monitoring the
vegetation dynamics.
There is a strong need for better defining the potential use of the 'simultaneous retrieval of (w S, )'
over the land surface.
Three main problems were identified and have to be addressed:

Simultaneous retrievals from multi-angular and dual polarisation measurements.
Further analyses of this question have to be carried out over a variety of vegetation types (for the
time being, a retrieval algorithm was only developed over soybean and wheat fields (Wigneron et al.,
1995)). Also the effects of vegetation type and vegetation moisture have to be investigated. These
questions should be addressed from experimental studies (from ground based measurements (van de
Griend et al., 1996) or possibly from airborne interferometric surveys) and from modelling studies
based on the radiative transfer model which accounts for the vegetation structure and the vegetation
moisture content (Ferrazzoli et al., 1995, 1996).

Mixed Pixels
Since the spatial resolution of SMOS is larger than 20 km, the application of the algorithms has to
be investigated over mixed pixels including a variety of soil surface types (several crop covers,
forest, open water, rivers, urban areas). This question should be addressed by both airborne
experiments and simulation studies.

Rugged Terrain (including the effect of surface roughness and topography).
Soil moisture retrieval algorithms were developed and tested from data acquired over flat terrain.
The possibility of applying them to rugged terrain (including the effect of small-scale effects of
surface roughness and large-scale effects of topography) has to be investigated.
This question should be addressed by both airborne experiments and simulation studies.
Proposed Experiments & Sites:
Test Site
Main
&
Main Characteristics
Investigators
Proposed studies
-crane-based
-Simultaneous Retrievals of wS and  from multi-angular
-variety of crop types measurements
-crop cycle monitoring -Dependence of the model parameters on vegetation structure
INRA Avignon
and moisture content.
Univ T Vergata, Roma
-Modelling of vegetation effects
TUD, Cophenhagen
CESBIO & CNRM
Washita (USA)
-airborne data
-Soil Moisture mapping from airborne data
-several flights
-Analysis of the effects of soil properties in the soil moisture
USDA
patterns
NASA
INRA-Avignon
(France)
Univ. of Reading
(UK)
Soil Dept. ( Reading)
Inst of Hydrology
-crane-based
-variety of crop types
-Implementing the retrievals of wS from multi-angular data, for
a variety of vegetation types.
-Study of within-field variability of wS
-Retrieval of soil properties
C1.1.2 Assimilation of Soil Moisture data in meteorological and hydrological models
3
SMOS will provide soil moisture data at a regular sampling rate of about 2-3 days. The
assimilation of time series of surface soil moisture in meteorological models has already been
investigated (Calvet et al., 1998). The work was based on times series of ground measurements of
surface soil moisture. The studies should be now carried out based on time series of brightness
temperatures.
Similar studies should be carried out for assimilation in hydrological models.
These studies should define: (a) the best-suited assimilation method, (b) the requirements for
implementing the assimilation method and (c) the improvements obtained in model forecasts from
assimilation of TB, for both hydrological and meteorological studies.
Proposed Experiments & Sites:
Test Site
& Main
Investigators
Main
Characteristics
Institute of Hydrology, -crane-based (SWAMP)
Wallingford (UK)
radiometric data
-crop cycle monitoring
Inst of Hydrology
Soil Dept. ( Reading)
Proposed Studies
-assimilation of soil moisture in hydrological & meteorological
models
-use of SMOS data to compute runoff
-aggregation of fluxes and problems of scaling (use of
scintillometers)
Ardeche Basin, France -rugged terrain
-assimilation in hydrological model over a catchment with
-coupled hydrol. model strong topographic effects
LTHE (Grenoble)
(lateral / vertical fluxes)
-analysis of wS redistribution by lateral fluxes
INPG Grenoble
Orgeval (France)
CEMAGREF
CETP Paris
~ flat catchment
-assimilation in hydrological model over an agricultural
-previous experience in catchment
use of radar data
-conceptual rainfall/runoff model
Valentian region & La -Southern environment
-Use of SMOS observations to retrieve environmental
Mancha (Spain)
-Network
of
WS characteristics (soil properties, vegetation variability, ...).
measurements
-Analysis of desertification processes
Univ. of Valencia
Univ. of Castilla
Meteo-France
(Toulouse)
-ground-based
radiometric data
-long term (> 1 year)
Meteo-France/ CNRM -past experience with
INRA Avignon
MUREX experiment
- Assimilation of time series of TB in a land surface scheme
(ISBA) to retrieve soil moisture (W2) and soil properties.
-assimilation of SMOS data for mixed pixels (simulation over
GEWEX sites)
IPSL Site Palaiseau
(Paris, France)
-
-ground-based
radiometric data
-long term (> 1 year)
assimilation of TB data in a land surface scheme (SISPATRS)
comparative analysis of different assimilation methods
-
IPSL (LMD & CETP)
CEA
CEMAGREF
Univ of Paris
C1.1.3 Forest Studies
4
The microwave signature of forests should be investigated from both experimental and modelling
studies.
There are two main interests in this characterisation:
(1) the SMOS measurements could be useful to retrieve forest characteristics (biomass, etc..).
(2) the signature of forests should be known for soil moisture retrievals in mixed pixels, including
forest cover.
Up to now, few investigations covering L band have been carried out. They are based on a physical
model (Ferrazzoli and Guerriero, 1996) and on a model with parameters optimised to fit experimental
data (Chauhan et al., 1999)
Some analyses based on measurements at higher frequencies have been carried out over the boreal
forest (Hallikainen et al., 1988) and the "Les Landes" forest (Wigneron et al., 1997).
Test Site
Main
Characteristics
Boreal Forest, Finland -crane-based and airborne
data
HUT, Helsinki
-long experience in SAR
and radiometric studies
"Les
Landes", -helicopter-mounted
Bordeaux (France)
measurements
-long experience in SAR
INRA (Bordeaux & and radiometric studies
Avignon)
Univ T Vergata, Roma
CESBIO France
Meteo-France/ CNRM
CETP
C1.2
Proposed Studies
-
Analysis of the discrimination capabilities for forest
mapping (biomass, ...) and surface characterisation
synergistic use of radar and radiometric data
-
Capabilities of Biomass retrieval over coniferous forest
(sandy soil)
Modelling of the forest microwave emissivity
-
RECOMMENDATIONS
The group endorses the SMOS mission objectives and requirements as expressed
in the Proposal to ESA.
C1.2.1 Image Reconstruction.
We recommend, as a first priority, the full analysis of the existing data set acquired
in Avignon (April 99) by the MIRAS demonstrator.
The scene includes well-contrasted areas (smooth strips at different soil moisture content, a
5m X 5m pool included in a large rough and dry field)
Up to now, this is the only data set available to demonstrate the Image Reconstruction process
required to retrieve Brightness Temperature from a 2-D interferometric radiometer over a natural
target.
This information would be of key interest for the development of future instruments (the HUT 2-D
radiometer) and for a possible refurbishment of the MIRAS demonstrator.
This step appears to be the first basic milestone for the SMOS mission over land surfaces .
C1.2.2 Algorithms
Retrieval from multi-angular data:
5
Investigations of the capabilities for simultaneous retrievals of wS and  from multi-angular data
should be extended to a variety of vegetation covers (different crop types, natural vegetation covers,
fallow, grassland, sparse forests,...).
For the time being, an algorithm was tested over soybean and wheat covers (Wigneron et al., 1993,
1995). Simulation studies of SMOS retrieval capabilities have also been carried out based on the
expected SMOS multi-angular and dual polarisation capabilities (Wigneron et al., 1999). The effects
of the vegetation structure and the moisture content of vegetation should be investigated for a variety
of vegetation canopies (crops, fallow, grassland, natural areas, ...).
Proposed work:
- Experimental studies from ground or airborne multi-angular measurements, over a variety of crop
covers. Analysis of the relationship between the model parameters and the vegetation structure and
moisture content from ground-based measurements.
- The possible use of data sets from the USA should be investigated.
-There is a strong need for building a conventional L-band radiometer to carry out the
experimental work.
Mixed pixels:
Very few works have been carried out up to date to address the problem of mixed pixels. Most of
the time, a large variety of surface cover types (agricultural areas, forests, open water, urban areas, ...)
will be included in the large-scale SMOS pixels.
There is a strong need to test and validate retrieval algorithms over mixed pixels.
Several problems have to be addressed:
- Defining in which surface conditions (in terms of % of surface areas, biomass .. of the different
cover types), can the retrieval algorithms be applied over mixed pixels.
- What are the expected retrieval accuracies depending on a large variety of surface cover types?
- What are requirements in the accurate knowledge of the areas covered by the different cover
types?
These questions could be addressed by both experimental measurements (from high altitude
airborne measurements) and modelling works.
The models can be based on scene reconstruction, which consists in building a scene including a
variety of surface cover types. The simulation is based on coupled crop models (simulating the crop
growth for a variety of crop types), SVAT models (simulating the surface fluxes and variables:
surface temperature, soil moisture, ..) and radiative transfer models (simulating the microwave
brightness temperature).
Topography and Surface Roughness effects.
There is a need to test and validate retrieval algorithms over pixels including rugged terrain.
Models accounting for topographic effects should be developed and tested from airborne experimental
campaigns. The effects of seasonal change in soil roughness conditions (in particular over agricultural
areas) should be also investigated from both simulation studies and experimental airborne data.
Forests
Work has to be carried out to analyse the microwave signature of forests at L band (see previous
section). This is important for retrievals over mixed pixels, where forests are often present. The
different forest types should be investigated (boreal, coniferous, temperate, deciduous, and
Mediterranean). This work should be carried out with the aid of physical models, useful to interpret
the microwave signature of forests: experimental data, on their hands, are needed to calibrate and
validate models.
As for other objectives, there is a strong need for an L-band radiometer to carry out the
experimental work
6
Analysis of the SMOS capabilities in the northern region
The northern region (including boreal forests) represents a very large region where the L-band
radiometric data could be useful to retrieve surface characteristics (forest biomass, soil moisture over
sparse forest covers, soil state, etc...)
The capabilities of SMOS to retrieve surface characteristics in the northern region (in conditions
of sparse coniferous forest, frequent snow cover, open water surfaces ...) should be investigated. This
work also includes the analysis of the capabilities to discriminate between frozen and thawed soils,
wet and dry snow.
C1.2.3 Data Sets:
There is a strong need to build experimental data sets including multi-angular, dual-polarisation
(and possibly multi-frequency) over vegetation canopies and bare soils surfaces (including several soil
roughness conditions). These data sets are required to develop retrieval algorithms, test and validate
theoretical models, analyse the effects of a variety surface conditions (soil roughness, frost and dew
effects, ...).
There are rather few data sets, which include multi-angular and dual polarisation TB measurements
at L-band, for a variety of surface conditions:
- INRA Avignon data sets: PORTOS -91 over a soybean crop and bare soils;
PORTOS- 93 over a wheat crop (including measurements of surface
fluxes) and bare soil surfaces (including a variety of soil roughness conditions).
Frequencies range from 1.4 to 90GHz (1.4, 5, 10.6, 23.8, 36.5 and 90 GHz)
- University of Bern data set:
several data sets over a variety of crops, including dualpolarisation and multi-angle data. However, the frequencies are higher than 3 GHz.
- available data sets in the USA:
the southern Great Plains 1997 experiment (SGP97) data is available on
http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/SGP97/sgp97.html
as well as several other data sets that can be accessed through
http://hydrolab.arsusda.gov/
It is expected that USDA will be adding to this site three years of truck data from early 1980s
experiments to that site in the next few weeks.
C1.2.4 Calibration
Investigations aimed at defining possible sites for after-launch calibration are required.
Possible sites are
- Ocean
- Antarctic and Arctic areas
- Desert (Sahara, ..)
- Tropical Rain Forest ...
Selected targets should have a homogeneous emissivity (over an area of about 100 X 100 km). The
surface temperature of the sites could be derived from Thermal Infrared remote sensing data, obtained
in clear sky conditions. The emissivity of the site should be stable and known a priori, or should be
computed with an accuracy of about +/- 1 K.
C1.2.5 Validation of retrievals
For the time being, the sites are the same as those listed in the initial SMOS project:
-Savannah
7
-Sites included in the GEWEX project
-Valentian region and La Mancha region.
C1.2.6 MIRAS simulator.
Is seems that there is a strong need to reduce the time of the simulations of the MIRAS simulator,
in order to have a more efficient and useful simulation tool.
Probably, inputs from the different groups (ocean, land, ice,..) could be given to the "Simulator
Team", in order to have more robust and rapid simulations of the microwave surface emissivity.
C1.3 References:
Calvet, J-C, Noilhan, J. and Bessemoulin, P., 1998, 'Retrieving the root-zone soil moisture from surface soil
moisture or temperature estimates: a feasibility study based on field measurements', J. Appl. Meteor. , vol. 37,
No. 4, pp. 371-386.
Chanzy, A., Schmugge, T. J., Calvet, J.-C., Kerr, Y., van Oevelen, P., Grosjean, O., and Wang, J. R. (1997),
Airborne microwave radiometry on a semi-arid area during Hapex-Sahel, J. Hydrol. 188-189:285-309.
N. Chauhan, D. Le Vine, R. Lang (1999), 'Passive and active microwave remote sensing of soil moisture under a
forest canopy', Proc. IGARSS 99, pp. 1914-1916.
Ferrazzoli P., Guerriero L., S. Paloscia, P. Pampaloni, 1995, 'Modeling X and Ka band emission from leafy
vegetation', J. of Electromagnetic Waves and Applications, 9:393-406.
Ferrazzoli, P., and Guerriero, L. (1996), Passive microwave remote sensing of forests: a model investigation,
IEEE Trans. Geosc. Remote Sens. 34:433-443.
Hallikainen M. T., P. A. Jolma and J. M. Hyypä (1988), 'Satellite microwave radiometry of forest and surface
types in Finland', IEEE Trans. Geosc. Remote Sens. 26(5):622-628.
Jackson, T. J., and Schmugge, T. J. (1991), Vegetation effects on the microwave emission of soils, Remote Sens.
Environ. 36:203-212.
Jackson, T. J., Le Vine, D. M., Swift, C. T., Schmugge, T. J., and Schiebe, F. R. (1995), Large area mapping of
soil moisture using the ESTAR passive microwave radiometer in Washita'92, Remote Sens. Environ 53:2737.
Kerr, Y. H., and Wigneron, J.-P. (1994), Vegetation models and observations - A review, in Proceedings of
Passive Microwave Remote Sensing of Land-Atmosphere Interactions, ESA/NASA International workshop 1993 (Saint-Lary), p. 317-344., B. Choudhury, Y. Kerr, E. Njoku, P. Pampaloni (Eds), VSP, Utrecht.
Kerr, Y. et al. (1998), MIRAS on RAMSES: radiometry applied to soil moisture and salinity measurements, Full
proposal to the AO Earth Explorer Opportunity Missions, Nov. 31, ESA.
Le Vine, D. M., and Karam, M. A. (1996), Dependence of attenuation in a vegetation canopy on frequency and
plant water content, IEEE Trans. Geosc. Remote Sens. 34:1090-1096.
Schmugge, T. J., and Jackson, T. J. (1994), Mapping soil moisture with microwave radiometers, Meteorol.
Atmos. Phys. 54:213-223.
van de Griend, A. A., Owe, M., de Ruiter, J., and Gouweleeuw, B. T. (1996), Measurement and behavior of dualpolarization vegetation optical depth and single scattering albedo at 1.4- and 5-GHz microwave frequencies,
IEEE Trans. Geosc. Remote Sens. 34:957-965.
Wang, J. R., Shiue, J. C., Schmugge, T. J., and Engman, E. T. (1990), The L-band PBMR measurements of
surface soil moisture in FIFE, IEEE Trans. Geosc. Remote Sens. 28:906-913.
Wigneron, J.-P., Kerr, Y. H., Chanzy, A., and Jin, Y. Q. (1993), Inversion of surface parameters from passive
microwave measurements over a soybean field, Remote Sens. Environ. 46:61-72.
Wigneron, J.-P., Chanzy, A., Calvet, J.-C., and Bruguier, N (1995), A simple algorithm to retrieve soil moisture
and vegetation biomass using passive microwave measurements over crop fields, Remote Sens. Environ.
51:331-341.
Wigneron, J.-P., Calvet, J.-C., and Kerr, Y. (1996), Monitoring water interception by crop fields from passive
microwave observations, Agric. Forest Meteor. 80:177-194.
Wigneron J.-P., Waldteufel P., Chanzy A., Calvet J.-C., Marloie O., Hanocq J.-F., Kerr Y. (1999), 'Retrieval
capabilities of L-Band 2-D interferometric radiometry over land surfaces (SMOS Mission)', in Proceedings of
the Specialist Meeting in Microwave Radiometry and Remote Sensing of the Environment, March 1999,
Firenze, Paloscia Ed., VSP, The Netherland., in press.
8
C.2 Ocean subgroup report
Chair Meric Srokosz
C21 Review of SMOS mission, objectives and requirement
The group reviewed the SMOS mission objectives for the oceans, as stated in the original
proposal, and endorsed the primary objectives:
Improving seasonal-to-interannual climate predictions
Improving ocean rainfall estimates and global hydrologic budgets
Monitoring large-scale salinity events
A variety of secondary objectives were also discussed (studies of the warm pool barrier layer;
large-scale fronts, e.g. warm pool; climate model initialisation; CO2 and SSS variations). A specific
objective that the cryosphere group should consider further was thought to be the determination of
Arctic summer sea ice concentration (L-band allowing discrimination between melt ponds and water).
The requirements for SSS measurements were also considered briefly and it was agreed that the
proposal requirements of 0.1psu over a 200km box and 10days average, and 1psu over a ~30km box
for a single retrieval were reasonable ones to proceed with at this stage. Suggested requirements were:
for large-scale fronts 0.5-1psu, 100km, 2-3days; model initialisation 0.1psu, 100km,
monthly/seasonal; CO2 studies 0.1-0.2psu, 100km, 2weeks; sea ice concentration 50km, few days.
More refined estimates of the requirements would depend on further studies of the impact of SSS data
on achieving the primary and secondary objectives.
C22 Scientific issues
1) The initial discussion focussed on the problem of sea surface roughness / foam / wind speed
effects on the L-band brightness temperature. Observations are very limited. Existing model suggest
that Tb/U10 ~ 0.3K/ms-1 depending on the incidence angle and on the polarisation, and a possible
azimuthal variation of TB ~ 0.3K (v-pol), 0.1K (h-pol). However significant differences exist
between models. There is a clear need for experimental measurements (both tower based and
airborne) to investigate this problem. The need to measure the small-scale waves and foam coverage,
as well as wind speed and direction, is important. In addition, non-local effects, such as swell, could
influence the brightness temperature and may not be able to be parameterised in terms of the wind
speed and azimuth (look direction relative to wind direction).
The possibility of obtaining wind information from other sources (other satellite sensors, e.g.
SeaWinds, or met. models) for SMOS was discussed. This raises the issue of how «simultaneous» the
winds speed measurements need to be to recover SSS to the required accuracy, and suggests that a
sampling simulation should be carried out to look at this. Based on some model results, it may be
possible to obtain an estimate of wind speed, to an accuracy of ~4ms -1, from the dual polarisation
measurement of SMOS itself. Unfortunately the emissivity models are tuned to data at higher
microwave frequencies and need to be validated by measurements at L-band. A further issue is the
impact of the within-footprint variability of such effects.
Given the sensitivity of the SSS to SST and wind speed effects, it is necessary that the brightness
temperatures be well calibrated (both absolutely and relatively), and that the instrument has high
stability.
2) Atmospheric effects, specifically rain, are not well understood. Models exist but have not been
tested at L-band. This may be possible by carrying out an experiment using an upward pointing
radiometer. The effect of rain on the sea surface (through raindrop impact generated waves or
damping of small waves), and so on the L-band brightness temperature, is probably a second order
effect.
9
3) The development of algorithms to retrieve SSS from the measured brightness temperature was
discussed. This is a non-trivial problem given the geometry of the SMOS measurements and the
variations of incidence angle and footprint size. A variety of approaches are possible.
4) The problem of Faraday rotation correction was discussed briefly, but there was no one present
(at that time) who had expertise in this area. It was suggested that expertise existed (Waldteufel, Le
Vine, Yueh) that could be made use of for this problem. Preliminary studies by Waldteufel indicate
that it should be a minor effect.
5) A number of scientific / algorithm development studies were discussed:
a) study of the wavenumber / frequency spectrum of SSS - what can SMOS resolve?
b) the impact of SSS data in models - how «poor» can SMOS be, but still useful?
c) comparison of assimilation of SSS and direct assimilation of the brightness temperatures
d) access to MSMR (ISRO) data for studies of wind impact at 6GHz, also access to US Lband data
e) a study of the decorrelation properties of the SMOS SSS measurement system
f) use of the experimental data to refine emissivity models and a comparison of existing
emissivity models
g) testing / refinement of models of rain effects at L-band
h) end-to-end simulation of SSS retrieval using simulator, including improved input to
simulator for ocean, and incorporation of better emissivity model. It was suggested that the
simulator be split into two parts: simulation of TB from geophysical parameters, then
simulation of SSS from TB.
i) studies of operational cal/val and linked to availability of SSS data from existing and future
programmes (CLIVAR/GOOS/ ARGO/…)
C23 Priorities
1) Experimental measurements of the sea surface roughness / foam / wind speed dependence of the
L-band, H & V-pol, brightness temperatures, over a range of incidence angle (0-60˚), wind speed (at
least 0-15m/s) and SSS and SST. It is necessary to investigate the importance of non-local effects
such as swell and whether all these effects can be parameterised in terms of wind speed and azimuth
(look direction relative to wind direction).
2) Accurate (relative and absolute) calibration of the brightness temperatures, and stability of
measurements, needs to be achieved. In simple terms, the present error estimates are based on a
sensitivity of 1 to 1.5K. A better sensitivity is desirable. This is an issue that the calibration / image
reconstruction group should address. The needed absolute accuracy is probably less than the relative
one (to measure space and time gradients): this should be looked at by the ocean group.
3) Given the geometry of the SMOS measurements and the consequent variation of incidence
angle and footprint size, it is necessary to study the best approach to retrieving accurate SSS from the
brightness temperatures.
4) Studies of the impact of SSS data on achieving the SMOS ocean objectives.
C24 Actions
1) Experimental measurements at the Barcelona (Casablanca) tower are being planned for summer
2000. Members of the subgroup, working with the campaigns subgroup, would investigate the
availability of the instruments for this experiment (Jordi Font acting as co-ordinator).
2) A workshop for those interested in the problem of SSS retrieval would be convened around
Sept./Oct. 2000 (possibly at LODYC, Paris), to work on the problem. Input from members of the
image reconstruction subgroup would be necessary at that time.
3) ESA to investigate access to MSMR (ISRO) data and US L-band data.
C25 Summary of recommendations
10
The key recommendations are those relating to the characterisation of sea surface roughness / foam
/ wind speed effects at L-band, to the calibration of the brightness temperatures, and to the accurate
retrieval of SSS from the measured brightness temperatures (see priorities and actions above).
It was stated that ESA was not in a position to fund all the studies that could be carried out, and the
possibility of obtaining funds from the EU Framework 5 programme was noted.
C.3 Image reconstruction
Chair, Markus Peichl, DLR
The working group on "Image reconstruction" (about 15 people from public research labs, space
agencies and industrial companies) identified and prioritised the following key areas to be addressed
during a phase A/B study of the anticipated SMOS project:
 Modelling of the instrument,
 Image reconstruction algorithm development and testing,
 Error compensation
 Calibration.
 Specific steps for the near future.
The "Image reconstruction" group's understanding of the various problem areas, proposed ways for
their solution, and recommendations are outlined below.
C31 Modelling of the instrument
The development, specification, design, and construction of an advanced scientific instrument such
as the SMOS sensor demands for a highly accurate and fully comprehensive tool to analyse its
performance under all operational conditions. The results of such an analysis represent the basis and
guidelines for the different steps of the overall instrument's production.
To meet those requirements in our case, it was proposed to use an existing simulation computer
code developed by the UPC for the earlier ESA supported MIRAS project as a starting basis. The
group agreed that the code should be refined and increased in accuracy where necessary, and
completed to fulfil the demands above. It was suggested not only to simulate the instrument in a
stand-alone operation, but also to allow the simulation of complete sequences of the anticipated
SMOS mission to measure soil moisture and ocean salinity.
C32 Image reconstruction key algorithm development and testing
For our understanding, "image reconstruction" covers the mathematical operation to convert the
measured data set from its original spatial appearance (correlation products) to the final, more user
friendly form (brightness temperature maps). While in an idealised case this could be a simple Fourier
transform, for our more complicated imaging system this no longer holds.
The group identified hereafter two main approaches to be useful for the SMOS instrument's
imaging strategy under operational conditions. In a short form notation the algorithms are called
"Band Limited Reconstruction" and "Extended clean approach". First one is under current
investigation at CERFACS and the second one at UPC. It was decided to use and further investigate
both approaches for the SMOS project to capitalise on both efforts.
The group identified as well the need for the generation of theoretical standard scenes to use for a
performance analysis of the algorithms. Furthermore the use of measured data was strongly
recommended, although no high spatial resolution data at L-band are currently available. The
following experimental equipment were mentioned: the ESA L-band demonstrators MIRAS (11
elements airborne type, built during the MIRAS project) and LICEF (ground based 2 elements type,
currently under production at ESA; the HUT airborne (36-elements) L-band demonstrator, to be
completed in fall 2000; an US X-band ground based instrument; the DLR Ka-band ground based
interferometer, to be extended to L-band within the next few months.
11
Separately identified was the problem arising for image reconstruction in the case of the
malfunction or loss of a few receivers or correlators, which leads to gaps in the measured twodimensional visibility function. All concerned group members (CERFACS, DLR, and UPC) will bring
in their experience from own investigations to address this problem, which is also related to the issue
of error compensation.
C33 Error compensation
The task of error compensation addresses the imperfections of each instrumental error source,
which is inherent to a real system. In the case of the SMOS sensor those sources are mainly generated
by different receiver and correlator transfer functions in amplitude and phase representing electronic
errors, and out-of-plane and in-plane deformations of the antennas carrying structure due to thermal
influences in space representing mechanical errors. The impact of those sources on a final image is
the additional generation of linear and non-linear transformations, which have to be compensated
during the image reconstruction process.
Two solutions are currently proposed by the group to remove the major errors. One approach is the
software based redundant spacing calibration investigated by CERFACS, which can remove
extensively both linear electronic and mechanical errors. The second, hardware based approach, is
investigated by UPC and uses the controlled distribution of uncorrelated noise to remove linear phase
and amplitude errors as well as offsets. This accounts for electronic error sources excluding the
antenna features. Both approaches require a high stability and accuracy of the centre part of the
SMOS antenna array.
DLR proposed the use of artificial point sources located on the ground (e.g. in Polar Regions), to
benefit from the comparison with the ideal synthesised beam for error compensation purposes. It was
recognised that thereby harmonisation problems with the radio-astronomical society and other users
of this protected frequency band will occur, which have to be clarified soon. ESA and experiences of
American colleagues might support this process.
C34 Calibration
The task of calibrating an instrument is the process, which assigns the designated physical quantity
(e.g. brightness temperature) to the measured quantity (e.g. a voltage or a current). For the case of the
aperture synthesis principle, the calibration is much more complicated than for real aperture imagers.
Accordingly, the group takes several calibration procedures under consideration to achieve and
guarantee a certain absolute accuracy.
UPC investigates an approach using calibrated visibilities due to the accompanying measurement
of known noise sources whereby again the antenna features are excluded. A second approach is the
use of the Earth's homogeneous brightness temperature regions of sufficient extent to conclude on the
instruments transfer function. The group identified the following areas as possible candidates: the
rain forest (TBC), deserts, ice regions and sea zones (e.g. the Sargasso Sea, which has very low
variations in the salinity distribution). These regions have to be measured in a controlled repetitive
manner by ground truth measurements, supported by ground based (e.g. airborne) radiometers. For
that task, the support of the other science teams for land and ocean is required, in particular for the
choice of adequate regions.
As an additional calibration check, the use of the artificial ground based point sources is
anticipated, if their installation is possible.
C35 Specific steps for the near future.
Further on, the working group discussed the next steps to be taken within its area of identified
activities. As noted by ESA, the start of phase A of the SMOS project is anticipated for summer 2000
and no financial support can be expected until the Spanish contribution is assured. Based on that, the
group agreed on mainly two activities to be considered during the time up to the start of phase A
First the existing software simulator for the modelling has to be verified concerning accuracy, and
modified or completed where necessary. Taking advantage of its modular construction, the existing
code can be extended in a box-of-bricks manner by each contributing party, for instance the land and
ocean science groups, too. It was agreed that the leadership for that task should be located at UPC,
12
who incorporates new tools and guarantees the software maintenance. Additionally, UPC and ESA
held out a prospect of making available the code to all participants of the SMOS project, in order to
use it and test alternative improvements.
Second it was found to be helpful to support this by experiences gathered during measurement
campaigns with the MIRAS 11-elements demonstrator (e.g. Avignon campaign). Hereby the main
problems arose from mutual coupling of the antenna elements within the array and differences of the
receiver transfer functions (critical filter response) both leading to linear and non-linear errors in the
reconstructed image. Both error sources have to be known exactly to support any compensation
procedure. Therefore it was decided to check soon, with ESA's help, the achievable degree of error
compensation. In the case of a positive result, those error sources of the MIRAS demonstrator should
be measured exactly in a separate campaign.
The group finally discussed the problem of interference of the SMOS sensor with artificial sources
such as radar and telecommunication transmitters. It was understood that a map of known sources
around the world would be very helpful to address the problem in more detail. For the case of
unknown or statistically time varying sources (e.g. military operators) it is hard to get rid of the
problem. Generally a high out-of-band rejection of the receiver transfer function is of high
importance.
C4 CAMPAIGNS
Chair Niels Skou, Campaign Group helped by López, Ernesto
This section deals with pre-launch campaigns, that is, the campaigns that it is important to initiate,
or at least consider, as soon as possible. Some campaigns have long preparation times – if for example
special measurement equipment has to be developed – and activities must start soon.
Although the ability of L-band radiometers to measure soil moisture and sea salinity is well
demonstrated, there are a range of outstanding issues that needs clarification during Phase A. This is
especially true concerning the influence of sea surface roughness on salinity retrieval to the level of
accuracy intended in the SMOS mission concept.
C41. OCEAN
C41.1 Background
The L-band brightness temperature (TB) of the ocean depends on salinity (S), sea surface
temperature (SST) and wind speed (WS). The following considerations concern vertical polarisation
(V pol) and 50° incidence angle unless otherwise indicated.
The brightness temperature sensitivity to salinity is at best (warm ocean around 30°) TB / S =
1K / psu dropping to 0.5 K / psu at 10°C and 0.3 K / psu at arctic conditions around 0°C. Hence, to
find salinity in warms oceans to the 0.1 psu level requires radiometric measurements to better than 0.1
K AND knowledge concerning the influence of other effects to the same level. Requirements are even
stricter for cold oceans.
The sensitivity to SST is small at high salinities, and for 34 psu water we find TB / SST = -0.2 K
/ °C dropping to zero in arctic oceans around 0 °C. (For brackish water we find much larger
sensitivities, for example TB / SST = 0.5 K / °C at 14 psu largely independent on SST.)
The above considerations are based on well established models reflecting the fact that for a smooth
ocean surface the brightness temperature is found from simple calculations if the dielectric constant is
known – which it is with good accuracy.
Concerning the sensitivity to wind speed, the situation is less favourable. Several models are
around, but it must be borne in mind that they were often developed with focus at higher frequencies,
and they often disagree at L-band. Very few measurements are available.
13
TB / WS = 0.4 K / m/sec has been quoted in the past, based on simple models. The only
available V pol data seems to be “old” Hollinger measurements from the late 60’es indicating 0.2 K /
m/sec at 50° incidence, increasing to 0.3 K / m/sec at 20° incidence. One obvious weakness of the
above quoted figures is that they do not at all reflect the possible significance of azimuth viewing
angle, i.e. the polarimetric signature. So far, all polarimetric measurements have concentrated on
much higher frequencies. Also model work has focussed on higher frequencies and L-band results
must be regarded as indicative at best. The ESTEC model shows a brightness temperature variation of
0.3 K with azimuth angle (8 m/sec wind, 50° incidence, 10°C, and 35 psu). Simon Yueh’s model finds
a lower figure around 0.1 K.
C41.2 Basic Ocean Measurements
It is obvious that we need to carry out very basic and accurate measurements of the L-band
brightness temperature of the ocean as a function of wind speed and direction. The measurements
must cover a wind speed range of 0 to 15 m/sec and the full 360° azimuthal range (possibly only
slightly more than 180° for practical reasons). The incidence angle should ideally range from nadir to
60°, but bearing in mind the problems associated with nadir measurements, especially from a tower,
the practical range is 10° to 60°. At least H & V polarisation are required, but the full set of Stokes
parameters should be measured to get the job done properly. While measuring the brightness
temperature, a range of other measurements must ideally be carried out concurrently: wind speed and
direction, sea surface temperature, salinity, foam coverage, wave spectrum (well into the capillary
region), atmospheric conditions.
Precise measurements of ocean brightness temperature require precise knowledge of pointing
geometry. Take for example incidence angle: at L-band, 50° incidence the vertical brightness
temperature depends on incidence angle by some 2.5 K / °. Hence, to get an uncertainty in the 0.1 K
range, we need to control, or at least know, the incidence angle to better than 1/20 of a degree! This is
just possible with a high quality INU mounted directly on the antenna structure.
Measurements can be carried out from towers or aircraft.
The tower enables long time series covering a variety of wind speeds and weather conditions at
reasonable cost. The measurement geometry can be very well known and stable. All the above
mentioned support measurements can be carried out. The drawback is of course the local nature of the
measurements as only a limited number of suitable towers are available. It is proposed to use the
“Casablanca” tower in the Mediterranean Sea, the “North Sea Tower”, and “Harvest” off the coast of
California.
The aircraft offers much larger spatial variability, and it is possible to cover a range of conditions
from arctic to tropical regions. Oftentimes it is difficult or even not feasible to acquire the full set of
support measurements, and experiments must be tailored to cope with this. A difficulty of aircraft
measurements is the requirement for precise knowledge of pointing geometry, and aircraft attitude,
including the measurement thereof, becomes a major issue. Suitable aircraft must be identified.
Possible sites for aircraft missions are TBD, but a very useful mission could be carried out over the
Sargasso Sea having very uniform salinity and temperature but variable winds. Also, missions to cold,
if not Arctic, regions should be considered.
C42. LAND
Retrieval of soil moisture from L-band radiometry has been a very active science issue for decades,
and a large number of ground based experiments have been and are being carried out in the EU as
well as in the US. Also a large number of airborne measurements, ranging from detailed mapping of
specific sites to larger scale mapping of land areas, have been carried out, especially in the US. But
there are still important outstanding issues to be addressed during the campaign period.
C42.1 Test Sites
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A range of test sites has been used in the past and could still be interesting and available in future:

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ARDECHE (F)
VALENCIA/CASTILLA-LA MANCHA (S)
WALLINGFORD (UK)
WHASHITA (USA)
AVIGNON (F)
ORGEVAL (F)
PALAISEAU (F)
TOULOUSE (F)
FINLAND
FINLAND is noteworthy for its special character not only for activities related to soil moisture but
also for including snow, ice, etc.
C42.2 Science Issues


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Topographic effects
Vertical profile
Assimilation in models
Vegetation effects – investigating retrieval of vegetation parameters and upper limit.
C42.3 Criteria for test site selection
Due to the large number of sites available for land campaigns, no particular site is selected as
yet. However, the following requirement criteria may help in making a future decision:
 LATITUDE: the sites could be grouped according to latitude, and we could have
complementary NORTHERN-, CENTRAL-, and SOUTHERN-EUROPE activities.
 LARGE-SCALE versus SMALL-SCALE: according to the different site characteristics, the
experiments to be performed could be planned from these two alternative viewpoints, taking into
account that scale could refer to spatial and/or temporal scale. Obviously, a large-scale site could
gather a number of small-activities as well.
 HOMOGENEITY/NON-HOMOGENEITY: it is difficult to find a perfectly homogeneous site
of the size of one, or better still, two SMOS pixels. It is clear as well that this could also be a
classification criterion allowing a certain looseness to the concept of homogeneity. It will be
interesting to organise activities at a homogeneous site, probably at first, although it could also be an
interesting scientific objective precisely to study non-homogeneity and subpixel variability under
different conditions.
C43. CRYOSPHERE
Campaigns related to the cryosphere were not discussed during the Barcelona meeting. It is,
however, obvious that some effort is highly warranted, as very little, if any, L-band data is available.
This subject is an issue for the Cryosphere Group to consider in the near future. (see § C5 below)
C44. OTHER COMMENTS
Land applications prefer an imaging radiometer system due to the spatial variability, while ocean
applications may use a non-imaging system in some cases (if, for example, extreme sensitivity and
accuracy are required).
Both land and ocean applications should ideally be demonstrated with an airborne 2-D synthetic
aperture radiometer. 3 possible systems are available in the near future: The ESA MIRAS
15
demonstrator has the advantage that it directly represents the SMOS Y-shaped instrument. It is
intended for C-130 operation and has indeed flown in the past, but failed. It requires upgrading and
improvements – especially concerning reliability. The HUT U-shaped instrument is planned to be
available late 2000. It is intended to fly on the Skyvan, and is a second-generation instrument
featuring improved design and reliability. The GSFC 2-D demonstrator is planned to be ready in
2001, and it is an instrument where a set of antenna elements can be positioned within a certain
aperture and different configurations tested.
It should be noted, however, that both land and sea applications have been demonstrated
extensively during the past decade using the 1-D ESTAR. This has been very successful despite the
less favourable imaging geometry of ESTAR (through nadir cross-track “scan”).
C45. RADIOMETERS
Synthetic aperture radiometer systems for demonstration of land and sea applications have already
been discussed above. Development of alternative, (improved) 2-D airborne instruments is a major
task probably outside the scope of the SMOS program. So, this section deals with real aperture
radiometers able to carry out the necessary campaign measurements.
The fundamental problem at L-band is the difficulty to achieve a narrow antenna beam. We need
to measure the brightness temperature as a function of incidence angle in the range 10° to 60°. It is at
best questionable to use a system with a 20° beam for this purpose, due to the range of incidence
angles thus being integrated over!
If we assume that a 10° beamwidth is acceptable, we need an antenna with a diameter close to 1.5
m. That is a large antenna - especially for airborne use! Note that we could consider an antenna with
an aspect ratio of for example 2:1 resulting in a wider azimuth beam, but also a smaller structure. If
we consider an imager, things get further complicated as we require a conical scan with fixed
incidence angle in order to make proper measurements. Such a system may be feasible to fly on a C130, but it is obvious that a non-imaging instrument is much more straightforward.
Only very few available and suitable L-band instruments can be identified. JPL has just finished a
large aperture, non-imaging instrument intended for C-130 operation. It features L- and S-band
radiometers where the incidence angle can be varied between 30° and 50°. The antenna aperture is 1.2
m at L-band corresponding to a beamwidth in the order of 12°.
TUD has available a single channel, very accurate noise-injection radiometer with a non-standard
input band: 300 MHz centred at 1.5 GHz. The dual polarisation antenna has a 60-cm aperture
corresponding to a 24° beamwidth.
TUD is presently developing a polarimetric L-band radiometer primarily intended for inclusion in
the Ku & Ka band airborne, polarimetric system. This radiometer will be state-of-the-art featuring
total power receivers with internal 2-point calibration for optimum sensitivity and, at the same time,
accurate calibration. A fast digital correlator finds the 3’rd and 4’th Stokes parameters with very good
fidelity. The antenna is yet TBD, but a large aperture, possibly to be mounted on a C-130, is under
consideration.
UPC is developing a polarimetric radiometer intended for use on the “Casablanca” tower.
University of Reading has an L band Radiometer (on a boom) which is currently being used at the
Institute of Hydrology after completion during summer 1999.
C46. AIRCRAFT
The HUT Skyvan is attractive due to good availability and moderate operating costs. DLR has
access to research aircraft. The Technical University of Denmark (TUD) has a traditionally very good
cooperation with the Danish Air Force, and has carried out a great number of remote sensing missions
over the years. This has included imaging polarimetric radiometer measurements using a C-130. The
C-130 is attractive due to low installation cost (instrument on the open ramp), large range and
capacity. Drawbacks are operating costs and more limited accessibility. The UK Met Office operates
a C-130. Availability is unknown at present. NASA operates a range of research aircraft, including a
16
C-130, a P 3, and a DC 8. It must also be considered to which degree suitable radiometers may be
fitted into smaller aircraft equipped with a standard aerial photography hole, or a large cargo door.
The advantages are very good accessibility and modest operating costs. The drawback is limited
aperture. It must be recalled that in general attitude problems are larger for smaller aircraft.
C5 Recommendations of the cryosphere group
Martti Hallikainen
Scientific studies aim for understanding the behaviour of L-band emission from sea ice and snow
under various weather and seasonal conditions, factors influencing emissivity, characterising
emissivity with theoretical/semi-empirical models and, finally, developing algorithms to retrieve
target characteristics. Field campaigns are needed to obtain information for both model development
and to verify emission models and retrieval algorithms.
The following before-launch activities are considered necessary in order to prepare for data from
the space-borne SMOS interferometer. The activities proposed below are prioritised, with the first one
(A) in Categories 1 and 2 being the most urgent.
Although both Category 1 and Category 2 are important, collection of experimental data (Category
2) is considered to be the most urgent task.
Category 3 deals with the synergy between SMOS and other spaceborne sensors, primarily
microwave radiometers. In cryospheric applications multichannel (frequency, polarisation) data have
proved to provide better results than single-channel data. Hence, in each of the tasks of Categories 1
and 2, synergy between SMOS data and available/near-future spaceborne microwave radiometer data
should be studied. For this reason Category 3 is shown in these recommendations as a separate item,
rather than prioritising it against Categories 1 and 2.
C51 Scientific Studies and Algorithm Development
(a) Emission Behaviour of Sea Ice
Research on the emissivity behaviour of sea ice has since the launch of the SMMR sensor in 1978
concentrated on the frequency range of 6.6 to 37 GHz and, more recently, on the frequency range of
the SSM/I sensor, 19 to 85 GHz. Studies on sea ice emissivity focussed on frequencies below C-band
are scarce and the same applies to availability of sea ice brightness temperature data. Emissivity
models have been developed for higher frequencies, but they have not been verified at L-band.
The behaviour of sea ice emissivity at L-band under various weather and seasonal conditions as a
function of basic ice parameters (salinity, temperature, thickness, age, ice geometry) and SMOS-based
sensor parameters (incidence angle, polarisation) should be investigated and theoretical and semiempirical emission models developed and verified.
(b) Detection of Thin Ice
The relatively long wavelength associated with L-band may be useful for mapping ice up to 0.5
meters, depending on ice salinity and surface temperature. This is important because the distribution
of heat loss from ocean to atmosphere in winter is dominated by the distribution of open water and
thin sea ice. The heat loss through open water and thin ice can be two orders of magnitude greater
than through thick sea ice. Another reason is that the growth of thin sea ice is associated with a brine
flux to the underlying ocean and this in turn has a profound effect on the water mass properties of the
17
ocean. It is believed that the brine generated from new sea ice growth is an important driver of the
global thermohaline circulation
The possibility of discriminating thin sea ice and determining ice thickness should be investigated
based on progress in the development of ice emission models. Attention should be paid to identifying
the weather and seasonal conditions and ice parameters (salinity, temperature) under which
information on thin ice can be obtained. Thin sea ice algorithms should be developed and verified.
(c) Detection of Melt Ponds
The largest source of error in mapping Arctic sea ice concentration during the melt season is the
presence of melt ponds on sea ice. Ice concentration estimates as much as 20 % too low may result
from this, due to the poor capability of present algorithms, relying on the frequency range of SSM/I,
to discriminate melt ponds from open water. The salinity of water in melt ponds is much lower than
that of water between the floes. Therefore, the sensitivity of the L-band SMOS instrument to water
salinity has the potential to distinguish between melt ponds and the high salinity sea water. This may,
however, require observations at both L-band and shorter wavelengths.
The feasibility of using L-band data to discriminate melt ponds should be investigated. The
optimum frequencies for this algorithm should be determined, based on the availability of data from
other spaceborne microwave radiometers in the near future. The developed algorithms should be
verified.
(d) Determination of Ice Temperature
Based on experiments conducted previously with radiometers operating at C-band and higher
frequencies, C-band is the best frequency range for determining the temperature of the radiating
portion of sea ice. SMOS may contribute to ice temperature observations, because the penetration
depth at L-band is much larger than at C-band. Additionally, L-band observations are less sensitive to
various surface features that may cause errors in temperature measurement.
The capability of L-band radiometry to determine sea ice temperature should be investigated.
Additional observations at C-band should be used. The developed algorithms should be verified.
(e) Snow Accumulation over Ice Sheets
Low-frequency measurements provide good penetration for snow over ice sheets. The capability of
L-band radiometry to obtain information on snow layering in deep snow areas should be investigated.
C52 Campaigns
Experimental L-band data on sea ice and snow are needed urgently, accompanied with extensive
high-quality ground truth. In general, airborne campaigns are preferred due to their capability to
collect data on various sea ice types and snow scenes over relatively large areas. Ground-based
radiometers are useful for collecting long time series of data.
Airborne data collection should be started with conventional L-band radiometers. Later, twodimensional interferometric radiometers should be used in order to gain experience on deriving the
brightness temperature maps of cryospheric targets from their visibility functions. Comparison of
results obtained simultaneously with traditional and interferometric radiometers is necessary in order
to verify the interferometric data.
18
Data collection on sea ice has priority over data collection on snow upon ice sheets.
(a) Sea Ice
Airborne campaigns should be conducted in order to collect data to support activities discussed in
1A through D. Good ground truth data are essential. Campaigns should be conducted under various
weather and seasonal conditions in order to cover all typical ice/snow conditions. Measurements
should be conducted over the incidence angle range of SMOS using both vertical and horizontal
polarisation.
(b) Snow over Ice Sheets
Airborne campaigns should be conducted in order to support activities discussed in 1 E. Data
collection flights should be carried out over deep snow areas. Ground truth activities under summer
conditions should utilise existing research camps. The test sites should be large enough to allow
comparison of airborne data with those from the spaceborne AMSR sensors. The possibility of
combining these experiments with sea ice experiments should be considered.
C53. Synergy with Other Sensors
(a) Scientific Studies
Multichannel (polarisation, frequency) radiometer data have traditionally been used to maximise
information on a target. The feasibility of using SMOS data jointly with other data sets (AMSR, etc.)
for cryospheric applications should be investigated. For example, detection of melt ponds and
determination of ice temperature may require joint use of L-band and C-band data.
(b) Campaigns
Airborne radiometer measurements of cryospheric targets should be conducted simultaneously
with L-band radiometers and higher-frequency receivers operating at the AMSR frequencies (6.9 to
89 GHz). This would allow determination of synergy between various frequencies and polarisations.
D Concluding plenary session
During this session, summary of the work conducted in splinter meetings was presented and
discussed.
The splinter sessions enabled to address a few critical points and make things clearer as far as the
most urgent actions to be taken are concerned. This will contribute as an input to the work of the
Scientific Advisory Group to be set up by ESA. It was also a good opportunity for ESA
representatives to get better acquainted with the SMOS proposal group and vice versa.
To summarise, the main science questions appear to be the following:
1) Instrument and mission modelling, image reconstruction:
A simulator is absolutely necessary. We should capitalise on the one developed at UPC and
improve it, mainly on the surface emission modules. It is thus recommended that the simulator is
19
made available with a description (brief summary) of the different modules with inputs and outputs.
The different parts (instrument model, orbit, direct radiative transfer modules, inverse model) could
then be analysed by the different subgroups and more accurate/ appropriate models be submitted, in
view of comparing them and making available improved versions.
This simulator should also contain the ancillary data ingest part as it might be an important point.
The MIRAS 99 data set should be fully investigated.
2) Ocean
Work on this topic will be mainly on a better understanding and modelling of the physics of
measurements and notably sea state through ground experiments and modelling activities.
Perturbating factors (sun glint, faraday rotation etc…) should also be addressed more in detail
3) Land
The issues to be addressed are mainly to finalise and fully validate the simultaneous ( )
inversion algorithm, the mixed pixel contributions, rugged terrain (mountains) influence, root zone
soil moisture retrieval, and dew/frost actual impact on measurements.
4) Campaigns
It is obvious that we will need to carry out a number of experiments and for this we will need a
number of ground and A/C instruments.
The very minimum requirements are of:
- one instrument "demonstrator" (HUT instruments and/or refurbishing of the MIRAS
demonstrator after a full analysis of the March 99 campaign data)
- One instrument to be used at sea
- One instrument to be used at ground level over land for continuous measurements (see land
report)
- One instrument to be used either from the ground or on an aircraft for specific campaigns
However, there are almost no L band radiometers available and it will be necessary to buy/have
some made. Annex 3 gives an overview of what could be the specifications of such a radiometer.
On the space instrument level, the group considered that the C-band option was not to be
considered. However, they suggested further analysis of the polarimetric option (feasibility, induced
costs wrt scientific return).
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ANNEX 1 Final list of participants
Group
Anterrieu, Eric
Bará, Javier
Bayle, Franck
Borges, Andrés
Boutin, Jacqueline
Calvet, Jean-Christophe
Camps, Adriano
Caselles, Vicent
Corbella, Ignasi
Dechambre, Monique
De Rosnay, Patricia
Emelianov, Mikhail
Etcheto; Jacqueline
Ferrazzoli, Paolo
Font, Jordi
Gabarró, Carolina
Galle, Sylvie
García-Górriz, Elisa
González, Pablo
Goutoule, Jean-Marc
Hallikainen, Martti
Howden, Stephan
Isern-Fontanet, Jordi
Jackson, Thomas
Johannessen, Johnny
Julià, Agustí
Kerr, Yann
Knapp, Eric
Lagerloef, Gary
Lannes, André
Le Traon, Pierre-Yves
Le Vine, David
López, Ernesto
Martín-Neira, Manuel
Moreno, José
Müller, Thomas
Obligis, Estelle
Ottlé, Catherine
Peichl, Markus
Podaire, Alain
Porta, Albert
Ragab, Ragab
Readings, Chris
Remy, Fréderique
Rius, Antoni
Rousseau, Stephan
Saulnier, Georges M.
Schulz, Joerg
Sempere, Luís
Silvestrin, PierLuigi
Skou, Niels
Solimini, Domenico
Srokosz, Meric
Thibaut, Pierre
Tobías, Alberto
Torres, Francesc
Vall-llosera, Mercè
Vilà, Jordi
Waldteufel, Philippe
OMP/CERFACS
TSC-UPC, Barcelona
MMS
CASA, Madrid
LODYC, Paris
METEO-FRANCE, Toulouse
TSC-UPC, Barcelona
UV, Valencia
TSC-UPC, Barcelona
CETP IOTA, Velizy
LMD/CNRS, Paris
ICM-CSIC, Barcelona
LODYC, Paris
Università Tor Vergata, Roma
ICM-CSIC, Barcelona
ACRI, Sophie-Antipolis
LTHE, Grenoble
ICM-CSIC, Barcelona
CDTI, Madrid
MMS,
HUT, Helsinki
GSFC-NASA, Greenbelt
ICM-CSIC, Barcelona
USDA ARS, Beltsville
ESA-ESTEC, Noordwijk
ICM-CSIC, Barcelona
CESBIO, Toulouse
U. Massachusetts, Amherst
ESR, Seattle
OMP/CERFACS
CLS, Toulouse
GSFC-NASA, Greenbelt
UV, Valencia
ESA-ESTEC, Noordwijk
UV, Valencia
Dornier, Friedrichshafen
CLS, Toulouse
CETP-CNRS, Velizy
DLR, Wessling
CNES
MIER, Barcelona
Inst. Hydrology, Wallingford
ESA-ESTEC, Noordwijk
DPI/EOT, Toulouse
IEEC, Barcelona
ICM-CSIC, Barcelona
LTHE, Grenoble
DLR, Köln
UPV, Valencia
ESA-ESTEC, Noordwijk
Tech. Univ. Denmark
Università Tor Vergata, Roma
SOC, Southampton
CLS, Toulouse
ESA-ESTEC, Noordwijk
TSC-UPC, Barcelona
TSC-UPC, Barcelona
IEEC, Barcelona
IPSL, Velizy
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Eric.anterrieu@obs-mip.fr
bara@tsc.upc.es
franck.bayle@tls.mms.fr
aborges@casa-de.es
jb@lodyc.jussieu.fr
calvet@meteo.fr
camps@mirsl.ecs.umass.edu
vicente.caselles@uv.es
corbella@tsc.upc.es
Monique.Dechambre@cetp.ipsl.fr
pderosna@lmd.jussieu.fr
mikhail@icm.csic.es
je@lodyc.jussieu.fr
ferrazzoli@disp.uniroma2.it
jfont@icm.csic.es
car@acri.fr
sylvie.galle@hmg.inpg.fr
elisa@icm.csic.es
pgs@cdti.es
Jean-Marc.GOUTOULE@tls.mms.fr
Martti.Hallikainen@hut.fi
howden@nemo.gsfc.nasa.gov
jisern@icm.csic.es
tjackson@hydrolab.arsusda.gov
jjohanne@estec.esa.nl
ajulia@icm.csic.es
Yann.Kerr@cesbio.cnes.fr
knapp@mirsl.ecs.umass.edu
lagerloef@esr.org
lannes@obs-mip.fr
Pierre-Yves.LeTraon@cls.fr
dmlevine@priam.gsfc.nasa.gov
ernesto.lopez@uv.es
mneira@estec.esa.nl
jose.moreno@uv.es
Tomas.Mueller@dss.dornier.dasa.de
Estelle.Obligis@cls.fr
catherine.ottle@cetp.ipsl.fr
markus.peichl@dlr.de
Alain.Podaire@cnes.fr
aporta@mier.es
R.Ragab@ua.nwl.ac.uk
creading@estec.esa.nl
Frederique.Remy@cnes.fr
rius@ieec.fcr.es
rousseau@icm.csic.es
Georges-Marie.Saulnier@hmg.inpg.fr
joerg.schulz@dlr.de
lsempere@dcom.upv.es
psilvest@estec.esa.nl
ns@emi.dtu.dk
solimini@disp.uniroma2.it
M.Srokosz@soc.soton.ac.uk
Thibaut@cls.fr
atobias@estec.esa.nl
xtorres@tsc.upc.es
merce@tsc.upc.es
vila@ieec.fcr.es
Philippe.Waldteufel@ipsl.uvsq.fr
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Weber, Thomas
Wigneron, Jean-Pierre
Dornier, Friedrichshafen
INRA, Avignon
Thomas.Weber@dss.dornier.dasa.de
wigneron@frake.avignon.inra.fr
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Annex 2 Workshop Agenda
FIRST SMOS Workshop
BARCELONA
September 8-10 1999
Agenda
September 8 1999
14:00 General Introduction
Welcome and Logistics
Purpose of the meeting
Approval of agenda
Status of the proposal
J. Font
Y. Kerr
all
YK
15:00 Organisation of the project
Current status
ESAC review
Underlying science and scientific activities
15:30 Collaborations/contributions
Relevant European National plans and interests
CDTI
CNES
Other international interests
Presentation of the Soil Moisture Mission document
Presentation of the SSIWG outcome
Discussion
16:30 SMOS Simulator
Presentation of concept
Simulator development, image reconstruction issues
Discussion
PHW)
C Readings
P. Gonzales
A. Podaire
TBD
T. Jackson
G. Lagerloef
all (chair YK)
P. Waldteufel
A. Camps
all
(chair
17:30 Break
18:00 Demonstration of the breadboard UPC simulator
AC
September 9 1999
8:30
Science programme
Issues to be addressed
all (chair JF)
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9:00
Organisation of the splinter sessions
points to be addressed during the splinter session (see appendix 2)
YK/JF
organisation of the subgroups and chairs
expected outcome
9:30
Splinter sessions.
13:00 Lunch
14:30 Resume splinter sessions
16:00 Plenary
Chairs of splinter to summarise the results of the discussions
Chairs
General discussion of findings followed by
consideration of calibration and campaigns
Splinter
18:30 Adjourn for the day
In the Evening, Jordi Font is organising a "get together" dinner and has booked a restaurant
for the whole group
September 10 1999
9:00 Continuation of plenary discussion on image reconstruction, simulator, calibration and
campaigns
10:45 Break
11:00 Summary and discussion of findings
All
12:45 Concluding Remarks
YK
13:00 Adjourn and Lunch
24
Annex 3: Ground radiometer specifications
First draft ideas
1) General considerations
The radiometer should be L band (allocated frequency) with a standard antenna (i.e., no
aperture synthesis). For use at ground level and, eventually (TBC) on a helicopter or an air
craft)
Several instruments should be available with ;, in some cases dedicated uses, hence more
specific requirements.
The goal of the ground instrumentation is several folds:




Allow continuous monitoring of a given area "in the field"
Allow 2 polarisation measurements
Allow angular measurements
Could be put on an A/C or an helicopter
2) First go at the specifications
The above requirements translate into the following specifications. It is well understood that
they are not necessarily feasible and/or complete. This is intended to be a first go at the
specifications: the figures indicated generally refer to SSS requirements (in brackets for land)
Antenna:
Not too clumsy (horn) and usable on a mast ? patch?
Beamwidth of the order of 10 ° (3 dB)
Beam efficiency better than 90 %
No big side lobes
Two polarisations (H & V) polarimetric?
Easy sky calibration
Angular acquisitions (0 -50 ° not necessarily synchronous)
System :
Reasonable size and weight
Battery operated ?
Thermally controlled (-20 +50)
Minimum maintenance
Simple interface (data logger and computer (PC)
Water proof
Receiver:
1.4 -1.427
NEDT < 0.2 K for 0.5 s (ocean) or 0.5 for 1 s
Stability 0.2 K over a couple of days and 0.5 over a month (SSS) or 1 K over a month
25
Calibration relatively easy and not too frequent (typically once a month)
Data output:
Digital and straightforward (RS232) and eventually analog as well, including housekeeping
data (temp, date, angle, volts etc)
Power:
Input possible on batteries , A/C possible, or mains
Global:
Able to work without interruption for at least 2 months (SSS) (6 months) in all weather
conditions (frost, rain, wind, sun, ….) including salt water (SSS)
Able to work without human intervention (calibration, cleaning, pointing, data) for at least 15
days (SSS) (one week)
26