PhD position on Soil Moisture Remote Sensing
Estellus is a very young spin-up emerging from public research institutes in Paris, France, in the field of satellite remote
sensing of Earth’s surface and atmosphere. Estellus is offering a PhD position on Soil Moisture Remote Sensing.
Context: Quantification of the continental water is very important for a large range of applications at various spatial
and temporal scales, from climate and weather predictions to agriculture and water management. Under a changing
climate, evolutions in the continental hydrological regimes are expected, but the magnitude of the change is very
uncertain, with potential consequences on the water availability for the population needs. Nevertheless, despite their
importance, estimates of the major hydrological variables such as soil moisture are not readily available with the
required accuracy. Measurements of soil moisture are not performed on a routine basis, and large remote areas are
devoid of observations. Land surface models calculate these variables at a global scale but they face numerous
challenges. They are very sensitive to the parameterizations of the complex processes involved and to the lack of
information on important parameters such as soil texture. These models depend upon uncertainties in the atmospheric
forcing, and even when forced with the same meteorological observations, the model outputs can show significant
differences (see for instance the results of the Global Soil Wetness Project (GSWP) inter-comparison, Dirmeyer et al.,
2005; 2006). Last but not least, land surface models suffer from the absence of observations to evaluate their outputs.
Satellite remote sensing techniques can provide the needed observations, with the adequate spatial and temporal
coverage, but the accuracy is still debated and efforts have to be pursued to develop optimum products and evaluate
them, in complement to in situ soil moisture measurements.
Tasks: The objectives of the thesis is to produce satellite-derived soil moisture estimates for model comparison,
validation, analysis, and improvement, with the final goal of providing more reliable hydrological predictions under a
changing climate. For that purpose, the program of work will comprise: 1) the development of methodologies that
optimize the use of satellite observations for soil moisture estimation at global scales but using new available
measurements such as ASCAT (active microwaves) and SMOS (low frequency passive microwaves), 2) the
quantification the variability of the soil moisture since the 90’s at seasonal and inter-annual scales over the globe and
the identification of the factors that affected this variability, from both satellites and model outputs, 3) lastly, the
development of innovative methodologies for the assimilation of soil moisture information in land surface models.
1) Extension of the already existing multi-satellite product. Use of the method with more recent instruments such as
ASCAT (MetOp) and SMOS. Development and evaluation of the new products.
A methodology has also been developed at a global scale to produce soil moisture estimates from multi-satellite
observations (visible, infrared, passive and active microwaves) at 0.25°0.25° spatial resolution. It is based on the fact
that the signal received by the satellite is generally the combination of contributions from different surface
characteristics (vegetation, soil, snow, roughness, among others) and disentangling these various effects from the soil
moisture signal is difficult, when using a single frequency range. It combines multi-wavelength observations from
different instruments to benefit from their synergy and it has been tested over two years (Aires et al., 2005). The first
task will consist in extending this analysis to present time, to make it possible to analyze inter-annual variability, in
comparison with land surface model outputs. Use of the satellites available over long time series is required to produce
long time series of products, for climatological studies. However, new instruments are now available, with enhanced
sensitivity to soil moisture and transition to these new observations is expected.
In this framework, a similar methodology will be developed, using new instrument such as the ASCAT scatterometer
on board the MetOP satellites and the recently launched SMOS observations. With its low frequency (1.4GHz), SMOS
(http://www.esa.int/esaLP/LPsmos.html) is optimized for soil moisture estimation, with less sensitivity to vegetation
cover and access to soil moisture below the surface.
2) Inter-comparison of the existing soil moisture satellite products available since the 90’s with model outputs and in
situ measurements. Analysis of the inter-annual variability and the factors that affect it.
Several global data sets of satellite-derived soil moisture estimates now exist (our multi-satellite data set, the
scatterometer-derived data set from Wagner et al., 2003, the passive microwave data set from Owe et al., 2007). A new
approach based on un-supervised classification and complex metrics will allow the assessment of the differences,
between the data sets. A detailed estimation of the retrieval uncertainties will be done using theoretical model and
validation with in situ observations. This new consolidated dataset will include more than 15 years and will allow the
inter-calibration and validation of the instruments and methods.
Then the project will focus on the analysis of the variability of the soil moisture at seasonal and inter-annual scales.
Ancillary information such as precipitation, surface temperatures will be jointly studied, to analyze the impact of their
variability on the variability of the soil moisture. Potential effects of anthropogenic effects (e.g., changes in agricultural
practices or in anthropogenic pressure) will also be examined. Particular locations where changes in hydrology have
been diagnosed lately will be examined in more details. Climate experts will be involved in the analyses of this
variability and its relationship with other parameters, to help interpret the data. The expected results of this analysis will
be a quantification of the inter-annual variability of the soil moisture, along with a tentative interpretation of this
variability, in terms of climate variability and anthropogenic pressure.
3)
Toward assimilation in land surface schemes
Numerical Weather Prediction center just start to assimilate satellite observations for land surface applications. The
objective in this thesis will be to optimize the use of multi-satellite surface sensitive satellite observations within the
assimilation schemes, with the development of innovative methodologies that insure a consistent and efficient
assimilation of the surface products within the model (Aires et al., 2005).
References:
- Aires, F., Prigent, C., and Rossow, W.B., Soil moisture at a global scale. II - Global statistical relationships.
Journal of Geophysical Research, 110, D11, D11103, 10.1029/2004JD005094, 01 June 2005.
- Dirmeyer, P. A., X. Gao, M. Zhao, Z. Guo, T. Oki and N. Hanasaki, 2006: The Second Global Soil Wetness Project
(GSWP-2): Multi-model analysis and implications for our perception of the land surface. Bull. Amer. Meteor. Soc., 87,
1381-1397.
- Dirmeyer, P. A., 2005: The land surface contribution to boreal summer season predictability. J. Hydrometeor., 6, 618632.
- Owe, M., R. De Jeu and T. Holmes, 2007, Multi-Sensor Climatology of Satellite-Derived Global Land Surface
Moisture, Journal of Geophysical Research, doi: 10.1029/2007JF000769.
- Prigent, C., Aires, F., and Rossow, W.B., Soil moisture at a global scale. I - Presentation of the satellite observations
and analysis of their relations with in situ soil moisture measurements. Journal of Geophysical Research, 110, D7,
D07110, 10.1029/2004JD005087, 13 April 2005.
- Wagner, W., K. Scipal, C. Pathe, D. Gerten, W. Lucht, B. Rudolf (2003), Evaluation of the agreement between the first
global remotely sensed soil moisture data with model and precipitation data, Journal of Geophysical Research D:
Atmospheres, 108, 19, 2003, Pages ACL 9-1 - 9-15.
Requirements: Key requirements for this PhD position are scientific enthusiasm, strong quantitative and analytical
skills, advanced practical programming experience, the ambition to publish results in international peer-reviewed
journals (excellent written and spoken English is a requirement) and the willingness to communicate research results
and to interact within an international research environment. We welcome candidates with enthusiasm for collaboration
within a multidisciplinary team, as well as an aptness to pose and solve problems individually. Candidates should hold a
M.Sc. degree or equivalent in quantitative science (e.g. geo-science, remote sensing or applied mathematics) and have a
strong motivation to complement their past training. Applications from candidates who are close to completion of their
undergraduate studies will also be condidered. Experience with at least one of the following topics is helpful: advanced
statistical data analysis, satellite remote sensing, radiative transfer and continental hydrology.
Work place: Estellus is a young start-up that is hosted by two prestigious public research institutes in Paris: the Institut
Pierre-Simon Laplace (www.ipsl.jussieu.fr) in Paris VI University campus, and the Paris Observatory (www.obspm.fr).
This is an international, highly creative and dynamic work environment. The PhD candidate is expected to obtain
attractive competences in diverse fields such as statistical analysis, remote sensing of the environment or continental
hydrology and climate.
Practical information: The position is financed for three years by the European Marie-Curie Initial Training Network
Greencycles II (www.greencycles.org). The PhD student will be registered in one of Estellus partner institutions, the
Paris Jussieu University and will be co-supervised by a Paris Observatory partner. Training workshops for all of the
PhD students and post-docs employed by the network are an important component of the training programme. In
addition, collaboration with other partners is foreseen.
Employment follows the eligibility criteria of the Marie-Curie scheme, in particular regarding international mobility. At
the start of their fellowship, researchers may not have resided or carried out their main activity (work, studies, etc) in
France for more than 12 months in the 3 years immediately prior to the reference deadline for eligibility. Short stays
such as holidays are not taken into account. French nationals are eligible only if they have been active in research in a
third country for at least three of the last four years.
Salary follows the rules of the European Commission’s Marie Curie Actions which is significantly higher than
following the rules of the French public service. The 3-years position can start in September 2010. Estellus seeks to
increase the number of female scientists and encourages them to apply. Handicapped persons with comparable
qualifications receive preferential status.
Application: Please include in your application your motivation, curriculum vitae, copies of your high-school and
academic certificates, a list of publications/presentations/qualifications, and names and contact information of at least
two references. Please also attach the 1-3 most representative and valuable examples of your past scientific work
(submitted manuscripts will of course be treated confidentially). Applications should arrive before 31.05.2010, but will
be also accepted until the position is filled at: LMD, UPMC, case 99, Filipe Aires, 4 place Jussieu, F-75252 Paris
Cedex 05, France, or preferably via e-mail as one or two pdf-files to filipe.aires(at)estellus.fr or
catherine.prigent(at)obspm.fr. Regarding questions please also contact Dr. Filipe Aires via email
(filipe.aires(at)stellus.fr).