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1st International Earth Observation Convoy and
Constellation Concepts Workshop
Executive Summary
Prepared by
Reference
Issue
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Date of Issue
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Amanda Regan
EOP-SFT/2014-03-1801
1
1
29/07/14
Issue 1.1
RP
ESA UNCLASSIFIED – For Official Use
1
EXECUTIVE SUMMARY
The 1st International Earth Observation Convoy and Constellation Concepts Workshop were held at ESAESTEC in Noordwijk in the Netherlands on 9th, 10th and 11th October, 2013. The event was hosted by the
European Space Agency and co-organised with the National Aerospace and Space Administration
(NASA).
The workshop comprised seven plenary sessions, which were both presentation and discussion based.
Professor Volker Liebig, Director of ESA Earth Observation Programmes provided opening remarks.
The executive summary has been written as a standalone document (reference: EOP-SFT- 2014-03-1801)
and a detailed and comprehensive report including summaries of all presentations and discussions is also
available (reference: EOP-SFT-2014-02-1789).
1.1
Session 1: Key Science and Implementation Accomplishments from
Existing Constellations
The first session showcased the science and implementation accomplishments of existing in-orbit
constellations being operated by multiple agencies. The missions presented included: the A-Train,
Morning Constellation, A-Train – Calipso mission, TanDEM-X, Cosmo-Skymed and the Disaster
Monitoring Constellation (DMC).
Graeme Stephens (NASA-JPL) gave the keynote speech. His talk focused on the A-Train and its
augmented science return. The present Afternoon Train (A-Train) comprises five satellites flying at 705
km: Aqua, Aura, Calipso, Cloudsat and GCOM-W1. NASA operates the Aqua, Aura and Cloudsat missions.
CNES operate the Calipso mission and JAXA operate the GCOM-W1 mission. The A-Train multi-sensor
approach generates new data sets and new science, which provides an in-depth integrated view of the
Earth System (with a particular emphasis on atmospheric measurements). The experience of the JAXA
GCOM-W1 satellite entering the A-Train was presented. The implication of GCOM-WI joining the A-Train
and the main lessons learned were highlighted. The Morning Constellation/train was presented
(forerunner to the A-Train). It proved that multiple sensors flying along the same path, which look at the
same scene with the same solar geometry coupled to extensive validation efforts, provide critical intercalibration and validation data streams. These data provided information redundancy and gap filling for
time series data products. The experience of Calipso flying in the A-Train with Cloudsat was also
presented. Lidar and passive radiometry are sensitive to different light-matter interactions and therefore
lidars can be used to validate and constrain passive retrievals. Active measurements should be seen as an
essential part of a cloud-aerosol-precipitation climate observing system. Long-term measurements are
required to identify, understand, and characterize cloud-climate feedback and characterize key modes of
climate variability.
The German Aerospace Center (DLR) presented the TerraSAR-X-add-on for
Digital Elevation
Measurements (TanDEM-X) bi-static concept. The two X-band SAR satellites fly in a closely controlled
double helix formation with typical distances between 250 and 500 m. The main lessons learned and
critical elements were presented including: synchronization, calibration and mutual radiation. The
constellation capabilities were presented and applications were discussed.
The Cosmo-Skymed mission comprises four identical X-band SAR satellites. The dual use system is able
to support a number of applications including risk monitoring, ocean and ice monitoring, coastal
monitoring, forestry applications and urban planning. Application examples were highlighted including
observing the Louisiana oil spill, the Abruzzo earthquake and the Costa Concordia shipwreck.
Surrey Satellite Technology Ltd (SSTL) presented the Disaster Monitoring Constellation (DMC) series
comprises at present 5 optical satellites, which can provide daily global coverage. The capabilities of the
constellation were presented and applications were discussed. Future concepts were highlighted.
1.2
Session 2: Future Landscape 2020 and Beyond
The second session focused the future in-orbit landscape. The ESA Earth Explorer programme was
presented. The Copernicus programme and its evolution were discussed including the dedicated space
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segment known as the Sentinels satellite series. An overview of the EUMETSAT missions was provided
and discussed including Meteosat, MetOp, and JASON satellite series. Future series such as MetOp
Second Generation (MetOp-SG) and Meteosat Third Generation (MTG) were also highlighted.
National agencies such as DLR, JAXA and ASI provided overviews of their respective programmes,
detailed international cooperation efforts and presented possible future scenarios.
The World Meteorological Organisation (WMO) provided a vision of a space based observing system in
the 2020’s. It was highlighted that the WMO Integrated Global Observing System (WIGOS) focuses on the
integration of space and surface based observations. The Observing System Capabilities Analysis and
Review (OSCAR) activities were also highlighted.
1.3
Session 3: ESA Convoy Missions and Candidate Missions
This session focused the Sentinel-5 precursor mission and the ESA Earth Explorer mission candidate
mission known as Fluorescence Explorer (FLEX). FLEX is being designed to fly in convoy with Sentinel-3
(separated by 6 to 15 seconds). The science objectives focus on global mapping of vegetation
fluorescence, vegetation health status / stress identification, anthropogenic impacts (land use changes)
etc. The FLEX end-to-end mission performance simulator was also highlighted.
Sentinel-5 Precursor (S5P) mission was also presented. It will be the first spacecraft in series of
atmospheric observing systems within the Copernicus programme. It is a preparatory mission before the
launch of Sentinel-5 on-board MetOp-SG. S5P is scheduled for launch in 2015 and it is planned that S5P
shall follow the ground track of the American JPSS satellite (13:30 LT).
1.4
Session 4: Technological Challenges
This session focused on the technological challenges of flying spacecraft together. NASA lessons learned
in general were identified and discussed. These points addressed both lessons learned by the A-Train and
constellations in general. The end of mission planning challenges for the A-Train was discussed and the
Cloudsat battery anomaly was highlighted. The A-Train control box methodology was presented which is
a simple but effective way of safely controlling the separation between the A-Train spacecraft along the
orbit. A-Train flight dynamics and associated challenges were identified and presented and possible
options for future concepts were discussed. The Jason-1 End of Life Case Study was also presented. EOL
issues were highlighted which require codes of practice to be agreed on an agency and inter-agency level
prior to the event including establishing a means to coordinate and communication information.
1.5
Session 5: ESA EO Convoy Studies – Latest Results
The European Space Agency (ESA) is funding three exploratory activities (known as the EO-Convoy
studies). The aim of these studies is two fold: Firstly, to identify scientific and operational objectives and
needs which would benefit from additional in-orbit support. Secondly, to identify and develop a number
of cost-effective convoy concepts (comprising additional missions flying with European operational
satellites), which would meet these identified objectives and needs. Each EO-Convoy study is dedicated to
a specific theme:
 Study 1: Ocean and Ice
 Study 2: Land
 Study 3: Atmosphere
The user needs and the derived convoy concepts were presented and discussed. The user needs study
documents can be found on the workshop website http://congrexprojects.com/2013-events/13m12/home
the user needs focused on the extension of established spectral and spatial scales. For each study a
number of convoy concepts were identified. These are listed below.
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Convoy Satellite
Anchor Satellite
Study 1: Ocean and Ice Convoy Study
Passive C-band SAR
+
Sentinel-1 (selected for further study)
Active C-band SAR (InSAR)
+
Sentinel-1
X/Ku-band SAR
+
Sentinel-1
Thermal Infrared (TIR)
+
Sentinel-1
VIS/NIR/SWIR
+
Sentinel-1
L-band SAR
+
Sentinel-1
Laser altimeter
+
Sentinel-3 (selected for further study)
Passive microwave (L-band)
+
Sentinel-3
Ku-band Scatterometer
+
MetOp-SG (selected for further study)
Passive Microwave (L-band)
+
MetOp-SG
Passive C-band SAR
+
Sentinel-1 (selected for further study)
L-band SAR
+
Sentinel-1
MIR/TIR multi-spectral imager
+
Sentinel-2 (selected for further study)
Sparse array L-band SAR
+
Sentinel-1
W-band conical scanner
+
Sentinel-2
High resolution TIR
+
Sentinel-2 (selected for further study)
Multi-angle imager
+
Sentinel-2
S-band SAR
+
Sentinel-1
Broadband light source
+
MetOp-SG (S5)
UV-VIS multi-angle profiler/ mapper
+
MetOp -SG (3MI) (selected for further study)
UV/Vis spectrometer
+
Sentinel-3 (SLSTR)
NO2 Lidar
+
S5P
3 micron spectrometer
+
MetOp (IASI, S5) (selected for further study)
Aerosol lidar
+
MetOp -SG (3MI/UVNS)
Carbonsat (EE8) + FLEX (EE8) + BIOMASS (EE7)
+
Sentinel-3 (SLSTR)
Lidar
+
MetOp -SG (IR/MW sounders)
Multi-angle thermal infrared
+
MetOp -SG
Extended RO
+
MetOp -SG
Cloud Profiling Radar
+
MetOp -SG
Multi-wavelength cloud aerosol lidar
+
MetOp -SG (Imagers)
Cloud Profiling Radar + Multi-wavelength cloud aerosol lidar
+
MetOp -SG (Imagers)
Study 2: Land Convoy Study
Study 3: Atmosphere Convoy Study
Figure 1 List of Convoy concepts identified and assessed during all three Convoy Studies
1.6
Session 6: Future Concepts
Session 6 comprised three sub-sessions focusing on SAR concepts, thermal infrared concepts and future
concepts in general. The theme for all the presentation was a need for higher temporal and spatial
measurements to capture dynamic Earth system phenomena and the characterisation of Earth system,
element interactions e.g. Land – Atmosphere, Ocean – Atmosphere etc.
Future radar concepts were discussed. The next generation of atmospheric radars should be defined in
the context of multi-instrument observations in order to mitigate the ambiguities affecting atmospheric
remote sensing techniques. Atmospheric radars also measure the surface and with advanced processing
and re-tuning other phenomena can be measured. This would lead to different user communities using
the same instrument to measure different phenomena.
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Measurements of convective processes on a global scale were highlighted as an area where space-borne
measurements would be valuable.
Geo-stationary infrared imaging satellites coupled with LEO imaging radar satellites provide
measurement synergy e.g. GEO-IR satellites measure cloud shell/skin properties and the radar
measurements from LEO can penetrate the cloud and measure phenomena occurring inside the cloud –
when these measurements are coupled together then overall cloud processes can be better understood.
The use of active instruments for Earth system measurement was highlighted. A possible convoy
configuration comprising CryoSat-2 and ICESat-2 in the post 2016 time frame was presented. Bi- and
multi-static SAR concepts were presented including the SAOCOM companion satellite and DLR PicoSAR
concept.
The need for high-resolution thermal infrared data was emphasized. Current TIR instruments will soon
be beyond their nominal lifetimes with strong possibility of a data gap later this decade. The NASA
Hyperspectral Imager (HyspIRI) mission was presented. Architectures for future missions focused on
agriculture were identified. High-resolution thermal infrared sensors were also presented e.g. the IRIS-M
payload comprising high-resolution capabilities in the thermal infrared. Use of a high-resolution thermal
infrared instrument was emphasized to complement Sentinel-2 (extend capability beyond SWIR) and/or
Sentinel-3 (higher resolution TIR to act as a zoom lens to complement the TIR at 1 km).
The Next Generation Gravity Mission (NGGM) was presented by ESA, comprising more than one satellite
and international cooperation between ESA and NASA was particularly highlighted.
The Cyclone Global Navigation Satellite System (CYGNSS) is the NASA Earth Venture Mission selected in
2012. This constellation mission (eight satellites) uses GPS signals to understand the coupling between
ocean surface properties, moist atmospheric thermodynamics, radiation, and convective dynamics in the
inner core of a tropical cyclones.
1.7
Session 7: Programmatic Challenges
This session focused on the programmatic details of setting up and operating constellations. The A-Train
experience was presented. A-Train data from the individual sensors can be used together to exploit data
synergies e.g. near-simultaneity and different observation geometries. Measurement synergy has enabled
improved science product quality. This requires sharing of data at a low level e.g. radiance level (“level 1”).
Multi-satellite missions must be designed and built using a common set of consolidated requirements
Each A-Train mission was designed with stand-alone mission objectives and with identified synergies
with other mission to enable additional science e.g. Cloudsat and Calipso have individual science
objectives but together provide augmented science return. Each mission maintains its independence but
the operations of one mission cannot interfere or jeopardize the safety of the other mission. A
constellation level management framework is critical to the safe operation of the A-Train. For the A-Train
this is known as the Mission Operation Working Group (MOWG). Constellation level documentation and
information exchange is essential and the A-Train uses the Constellation Coordination System (CCS),
which is on-line tool enabling information exchange information, e.g. mission status and orbital data. An
open data policy is essential. A full science benefit cannot be achieved and the investment of flying a
constellation cannot be realized without an open data exchange. Careful calibration and validation on a
constellation level must also be addressed. Data merging, data management and data storage are critical
issues requiring resource allocation and careful definition.
Specific A-Train case studies were presented including the Parasol mission leaving the A-Train, the
Cloudsat mission re-entering the A-Train and Aqua satellite (A-Train anchor satellite) inclination
maneuver changes.
As more satellites are launched into space the idea of an international registry to mitigate close
approaches and collisions was presented. An international registry would lead to joint working groups,
information sharing, and joint analysis. In the short term NASA would like to collect point of contact
information from other operators to resolve these issues. Possible implementation activities were
presented.
Future convoys and constellations require a framework to establish expectations. This includes e.g.
international agreements, constellation level documentation and data sharing, agency activities and calls
which encourage convoys and constellations, operational configurations which allow safe multi-satellite
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flying, standardized policies and procedures which are independent of individual missions. There also
needs to be a basis for committing agency resources to constellation activities with dedicated constellation
level management and a promotion of multi-mission research.
1.8
Key Messages
Figure 2 provides an overview of the key messages from the workshop. The key messages are identified
and discussed in sections 1.8.1 to 1.8.4.
Figure 2 Workshop Key Messages
1.8.1
Future Constellation Science and Measurements
Key Message 1.1: Constellations must focus on cross cutting science
 Large cross cutting science problems (e.g., interactions between Earth science domains and
Earth science cycles such as energy, water and carbon) need to be identified and characterised
and any derived constellation concepts need to be mapped to this analysis.
 Constellations provide a unique opportunity to measure the interfaces and interactions
between Earth Science Domains.
Key Message 1.2: Constellations can exploit complementary measurements
 Cross-comparison of the same geophysical product using multiple observation techniques and
retrieval methods is essential to understanding the phenomena being observed.
 Active and Passive instruments
o Active and passive instruments provide complementary measurements. Using both
types of instruments together can provide excellent opportunities for cross comparison
and error checking.
o Measuring the same phenomena using different instruments based on different physics
leads to increased confidence that the process being measured is being properly
understood.
 Simultaneous measurements (separated in time, space and viewing direction etc)
o Identical/complementary measurements separated in time / space / both following a
reference ground track to capture dynamics processes.
o Measurement from e.g. limb and nadir viewing directions can be invaluable to
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characterise processes and phenomena occurring in three dimensions e.g. Earth
Explorer 8 candidate mission PREMIER and MetOp.
 Instruments in LEO and GEO
o Instruments in LEO and GEO can provide highly complementary measurements.
Key Message 1.3: Long term sustainable scientific data

The Earth System is a highly complex system with processes and phenomena occurring over a
wide range of spatial and temporal scales. Multi-satellite data sets show that these processes
and phenomena are all interlinked and fast processes project onto the longer scales. The key is
to understand how the system evolves through sustained and long-term measurements and not
just by providing short-term intermittent measurements.

The key is to understand how the system evolves through sustained and long-term
measurements. The design of scientific missions as independent experiments with a relatively
short life time and lack of firmly planned continuity affects the development of potential
constellations, which may be built-up in time.
Key Message 1.4: High resolution measurements
 Complex and dynamic phenomena require high-resolution measurements in both the spatial
and temporal domains.
 Higher resolution sensors are needed to capture smaller scales and characterise dynamic
cycles.
 Sub-daily revisit (which is possible with multiple satellites) is needed for many applications to
capture phenomena such as diurnal cycles etc.
 Examples requiring high resolution observations were cited across all Earth Science domains
e.g. the measurement of mesoscale and sub-mesoscale oceanographic features, improved wind
measurements, ocean and particularly coastal surface currents, land cover complexity and
dynamics (including cryosphere), surface energy balance, urban applications, water including
snow, snowfall and sea-ice, etc.
 Higher resolution measurement supports improved model development.
 Three-dimensional measurements are needed to comprehensively capture dynamic and
complex processes. One example cited was 3D vector motion.
Key Message 1.5: Constellation level data products

Constellation level data products must be identified and resources put in place to generate such
products.

Cross-comparison of the same geophysical product using multiple observation techniques and
retrieval methods is essential to understanding the phenomena being observed.

Merging data from multiple sensors with different observation techniques in terms of
geometry, co-registration etc. is not a trivial task and resources must be allocated for this task.
Key Message 1.6: Calibration
 Calibration is critical to ensure data consistency over long time series particularly for climate
monitoring.
 Robust calibration enables effective data merging from various sources and it allows data gaps
to bridged.
 One instrument acting as a reference calibrator can be used to enhance the return of other
instruments.
Key Message 1.7: Co-registration
 The issue of co-registration of multiple sensors flying in the train is a complex problem and
should not be overlooked. Issues such as differing sensor resolution and swath width must be
addressed including the problem of cloud movement and characterization.
Key Message 1.8: Instrument retrieval algorithms
 Instrument retrieval algorithms should be developed and reviewed with the same rigor as the
instrument engineering development.
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1.8.2
Constellation Lessons Learned
Key Message 2.1: Cooperative sensing requires a paradigm shift
• Flying in a constellation requires a shift in thinking from mission level to constellation level.
Acknowledgement that certain mission activities may impact other missions e.g. data sets, orbit,
downlink etc. These considerations need to be identified, communicated, managed and resolved
on a constellation level
• Missions flying in constellation cannot be considered in isolation. Cooperative sensing may add
some complexity and cost but ultimately it can provide great benefits and augmented science
return.
• Any developed mission must be able to stand-alone in terms of its science objectives and provide
augmented science return when flying together with other missions.
Key Message 2.2: Agency support and effective management at constellation level
• Strong agency support and vision are essential.
• Effective management at the constellation level is critical coupled to a coherent management
structure with clear decision boards
• For future convoys and constellations a framework is needed to establish expectations. This
includes e.g. international agreements and data sharing, agency activities and calls which
encourage convoys and constellations, operational configurations which allow safe multisatellite flying, standardized policies and procedures which are independent of individual
missions.
• There also needs to be a basis for committing agency resources to constellation activities with
dedicated constellation level management and a promotion of multi-mission research.
• Constellation level activities require careful planning and agreement e.g. manoeuvre campaigns
etc.
Key Message 2.3: Orbital considerations
• Definition of the reference ground track is critical.
• The use of control boxes or similar with buffers to maintain constellation safety is critical.
• Definition of the phasing at the poles is important to prevent satellite conjunctions
Key Message 2.4: Spacecraft Implications (highlighted & discussed during the workshop)
• BOL and EOL planning
o Mission objectives must drive the mission until the spacecraft health reaches a limit.
There is a time when the satellite needs to de-orbit from the constellation. BOL and EOL
planning must be identified, assessed and agreed at an early stage of development and
then periodically iterated as the spacecraft moves through its development and in-orbit
phases.
• Orbit choice
o The orbit choice may be a compromise between instrument capabilities and the science
benefits of flying in a constellation e.g. active instruments flying in a constellation at a
higher orbit.
o Definition of the reference ground track is critical.
o For EOL / de-orbit from the constellation an alternative orbit should be identified
before launch.
• Propellant
o Typically more propellant is required when flying in a constellation:
o Safe orbit insertion
o Safe in-orbit manoeuvres
o Safe de-orbit
o For the satellites operating within a constellation an understanding of the fuel budget is
critical e.g. consumption, use of fuel for unforeseen orbit manoeuvres.
• Flexible manoeuvre capability
o Flexible maneuver capability is strongly advised e.g. retro-firing capability
• Spacecraft modes
o For each satellite flying closely together within constellation, a full understanding of all
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possible spacecraft modes is seen as critical to prevent unforeseen close approaches e.g.
propulsive safe modes etc.
• Communication between satellites in the constellation
o Additional resources may be needed e.g. transponders etc to communicate with other
satellites in the constellation.
• Mass memory
o Depending on the design more mass memory may be needed.
• Interference
o Mutual irradiation from satellites flying together can be a design constraint.
• Uplink and downlink design
o When satellites are flying closely together the uplink and particularly the downlink must
be carefully assessed (particularly for satellites with high data rate sensors on-board).
• Programmatic impact
o When different satellites are flying together the programmatics of one satellite may
impact another particularly if one satellite is reliant on the measurements of another e.g.
different agency development cycles etc.
Key Message 2.5: Constellation can provide mission flexibility
• Constellations provide flexibility to address foreseen and unforeseen issues such as sun glint
mitigation etc e.g. the spacecraft can be separated and re-aligned etc.
Key Message 2.6: Established constellation agreements, policies and codes of practice
• For future convoys and constellations a framework is needed to establish expectations.
• Establishment of coherent constellation level agreements, policies and code of practice must be
signed by all parties addressing all phases of the mission lifetime e.g. orbit insertion, operation,
end of life (EOL) operations.
• A robust and transparent process for constellation issues is critical e.g. BOL, change requests,
EOL etc. Coordination rules, processes and plans have to be flexible and adaptable and
communication between the mission teams is critical.
• Establish what data should be shared and a means to coordinate and communication
information.
• Agreements are essential to ensure that there is a mutual understanding of the terms governing
the inter-agency relationship e.g. for the A-Train Contractor/private industry personnel
negotiate Technical Assistance Agreements, which are then signed by the individual mission
teams.
• A basis is required for committing agency resources to constellation activities with dedicated
constellation level management and a promotion of multi-mission research.
Key Message 2.7: Understanding differences when working in cooperation

Cooperation with other agencies (either at a national or international level) requires an
understanding of different cultures, different methods of working, different development cycles,
different time zones and different motivational factors. These aspects should not be under
estimated.
1.8.3
Highlighted Convoy Concepts
Key Message 3.1: Measurement combinations provide complementary measurements
 A suite of instruments is needed to measure from the top of atmosphere (TOA) to ground level.
 The A-Train is based on measuring the same phenomena with different sensors based on
different physics. This multi-sensor approach provides augmented science return across
different observations, platforms and sensors. This approach enables data products to be
independently calibrated.
 One example discussed focused on Calipso-Caliop (Lidar) and Aqua-MODIS, which provide
atmospheric retrievals based on different physics. Active instruments can validate the retrievals
of passive instruments. One example discussed focused on Calipso-Caliop (Lidar) and AquaMODIS, which provide atmospheric retrievals based on different physics. The Aqua-MODIS
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
retrievals rely on inputted light scattering models and these can be calibrated using the lidar on
board the Calipso spacecraft.
Measuring phenomena with different sensors based on different physics and obtaining similar
results provides confidence that the processes and phenomena are being well understood.
Key Message 3.2: Identical or complementary measurement combinations separated in
time / space / viewing direction
 Identical/complementary instruments can be separated in time (along or across track) and / or
space (distributed spacecraft etc.) to characterise dynamic phenomena
 Different viewing directions e.g. limb and nadir can be used to characterise processes and
phenomena occurring in three dimensions e.g. Earth Explorer 8 candidate mission PREMIER
(Limb) and MetOp (Nadir).
Key Message 3.3: Specific Convoy Concepts which were highlighted (non-exhaustive list)
 Laser and radar combinations
o Laser and radar instruments flying together in a coordinated way provide
complementary measurements, which, could provide cross cutting science and address
applications across numerous Earth Science domains. Examples included
Cloudsat/Calipso (A-Train), and the possible tandem operations of Cryosat-2/ Icesat-2.
 Higher resolution thermal infrared < 60 m – 250 m
o Measurements in the thermal infrared spectral range are needed for numerous Earth
Science domains.
o Current in-orbit TIR instruments e.g. Landsat-8-TIRS, Aqua/Terra-MODIS, TerraASTER etc all have limited lifetimes and if replacements are not launched then there will
be a strong possibility of a data gap later this decade.
o Multiple TIR channels are needed to separate emissivity and temperature.
o Mid infrared and thermal infrared are needed to measure fires and thermal hot spots
(with additional visible channels for context).
o To measure thermal anomalies a high dynamic range is required to mitigate detector
saturation.
o There is cross crossing science between land and atmospheric sounding communities
regarding infrared imagery
o Flying a thermal infrared imager with Sentinel-2 was highlighted.
 Bi-static and multi-static SAR
o Passive SAR concepts flying together with active SAR satellites were highlighted: single
pass and repeat pass interferometry in L-band (SOACOM-CS) and C-band (ESA EO
Convoy, DLR PicoSAR concept).
o Constellations of active SARs flying together. The TanDEM-X mission was presented
and future concepts such as bi-static SAR for applications such as ocean current
observation, soil moisture measurement, urban area characterisation and forest
tomography were also highlighted.
 Multi-frequency SAR
o Multi-frequency SAR measurements (SAR satellites of different frequencies flying
together) were discussed as a way to increase the dynamic range and due to different
responses build up a picture of phenomena being measured.
 Next generation Atmospheric Radar Satellites
o The next generation of atmospheric radars should be defined in the context of multiinstrument observations in order to mitigate the ambiguities affecting atmospheric
remote sensing techniques.
o Atmospheric radars can also measure the surface and with advanced processing and retuning other land surface phenomena could be measured. This would lead to different
user communities using the same instrument.
o A backscatter lidar to provide support data for other missions
 Earth Explorer Candidate Missions not selected were highlighted:
o PREMIER flying with MetOp
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
o CoReH2O (X/Ku-band SAR) flying with Sentinel-1
A backscatter lidar to provide support data for other missions
o The lidar can provide support data for existing missions to establish scene
characteristics e.g. remove unwanted clutter in the actual measurement such as the
presence of thin cirrus clouds
Key Message 3.4: Measurement synergy concepts

LEO and GEO concepts flying together
o Coordinated GEO and LEO satellites combinations were highlighted as a potentially
powerful technique to capture dynamic processes on global and local scales.
o One example: Use GEO IR satellites /LEO radar satellites to build up a picture of
global convection. The GEO-Infrared satellites measure cloud shell/skin properties
and the radar can measure phenomena inside the cloud.
1.8.4
Future Constellation Design
Key Message 4.1: Measurement Synergy

Missions can no longer be designed in isolation. When new missions are developed the existing
landscape and possible measurement synergies must be considered for augmented science
return. Constellation aspects should be highlighted in Agency calls e.g. ESA Earth Explorers etc.
Key Message 4.2: Copernicus Sentinels
• Copernicus represents a stable long-term programme for Earth Observation into 2030s. The
Copernicus Sentinels are a constellation infrastructure and possible synergies with other
systems should be explored. The Sentinels do not fly in convoy with each other but further
activities focused on synergetic use of Sentinel data and data augmentation on a constellation
level should be considered. Aspects such as Systems of Systems can be considered.
Key Message 4.3: Anchor Satellites
• Satellites such as EOS-Aqua, Landsat series and the planned Sentinels can provide long-term
anchor points for future constellations.
Key Message 4.4: Orbit Choice
• Constellation participation depends upon the attractiveness of the orbit.
Key Message 4.5: Data policy, data management and distribution
• Data policies vary across nations and national agencies therefore it is important to establish the
data policies at an early stage.
• The data combination, processing, distribution and storage for a constellation must be carefully
assessed and resources must be allocated.
• Merging data from multiple sensors with different observation techniques in terms of geometry,
co-registration etc. is not a trivial task and resources must be allocated for this task.
• Full science benefit cannot be achieved and the investment of a flying a constellation cannot be
realized without an open data exchange.
Key Message 4.6: Replenishment Strategy
• Any constellation must have a viable and robust replenishment strategy
Key Message 4.7: International Cooperation
• International cooperation is essential. Constellations enable international cooperation to ensure
an optimum return / effort ratio.
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1.9
Workshop Recommendations
Based on the results and discussion at the 1 st International Earth Observation Convoy and Constellations
Workshop, a number of recommendations were identified for future areas of further study. These can be
seen below.
Recommendation – Constellations to focus on cross cutting science
 The convoy studies focused on extending scales of known parameters. It was recommended to
open out this analysis away from incremental deltas related to known parameters and move
towards broader cross cutting measurement gaps which are needed to comprehensively
understand the Earth system e.g.:
o Characterising the interfaces and interactions between the various Earth system domains
e.g. cycles.
o Identifying and understanding the various flux exchanges and their impact on the Earth
System.
 Therefore, future science activities must focus on the interactions, interfaces and
connections between the classical Earth Science domains. These activities can provide a
roadmap for future constellations. One example provided was high-resolution evapotranspiration
measurement, which essentially connects the water cycle and the surface energy balance. This
approach would also benefit model assimilation e.g. land surface, land-atmosphere models.
Recommendation – Cooperative sensing
 There needs to be a fundamental paradigm shift towards ‘cooperative sensing’ when
defining new missions. New missions cannot be designed in isolation. At present Agencies select
missions often on a case-by-case basis.

A formal programmatic framework is required for constellation missions. This framework would
include elements such as rules for international or inter-agency cooperation, data policy,
information exchange etc.
Recommendation – Anchor Satellites
Copernicus is a constellation in itself. The Sentinels and other missions such as Landsat follow on
concepts etc can act as anchor satellites for additional missions.
Recommendation – Identified Convoy Concepts
A number of convoy concepts were highlighted. These included:
 A combination of passive and active measurements provides the most comprehensive
science return, due to synergy in information content. Laser and radar synergies were particularly
highlighted.
 Higher resolution thermal infrared (< 60 m – 250 m).
 Bi-static and multi-static SAR (C-band and L-band were highlighted)
 Multi-frequency SAR measurements comprising SAR satellites of different frequencies
flying together.
 The next generation atmospheric radars should be defined in the context of multiinstrument observations in order to mitigate the ambiguities affecting atmospheric remote
sensing techniques
 Earth Explorer Candidate missions which were not selected were highlighted e.g.:
o PREMIER (limb view) with flying with MetOp (nadir view)
o CoReH20 (X/Ku-band SAR) flying with Sentinel-1 (C-band SAR)
Recommendation
 It was highlighted that one area of improvement for future observing systems is the ability to
capture dynamic small-scale processes. For these types of observations high spatial
resolution and high temporal resolution were identified as critical. Examples included heat
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
flux characterisation, velocities, diurnal cycles etc.
A good sampling is required to capture dynamic behaviour and this requires combining multipoint measurement from convoys, constellations and other observing system such as GEO
satellites. Activities focusing on combining LEO and GEO measurements were highlighted.
Recommendation – Multi-Agency Constellation Handbook / Guidelines
Produce a multi-agency constellation implementation handbook / set of guidelines based on lessons
learned. This document can then become an agreed starting point for future international cooperation.
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