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POLINSAR Workshop 2003

Session: Theoretical Modelling

Chair/s: Thuy Le Toan and Paul Saich
 

1. Session highlights
Although the scheduled theoretical modelling session had only three oral papers, the use of physical models to interpret data or to derive inversion algorithms was present in several presentations and poster papers.
Most current theoretical models are not adapted to polarimetric and interferometric radar data, for which phase information needs to be estimated accurately. The difficulties in such modelling originate both in the detailed description of the medium and in calculations of higher order scattering.  For natural media such as vegetation, ice or soil, appropriate models are needed to understand the (few) experimental results and to assess the generality and robustness of inversion algorithms through model simulations.
 

2. Seed questions

Q1: Is  theoretical modelling useful?

Yes. Despite their complexity, physical models are essential for the development of inversion algorithms and the definition of optimum future systems.

Q2: Reasons for relatively little modelling work?

Lack of funding: In the remote sensing community, theoretical modelling is usually considered as upstream basic research, for which less funding is available compared to application-oriented studies.
Gap between electromagnetism and remote sensing communities: There are insufficient links between the two communities. For the electromagnetics community, studies of natural media may appear more complex and less rewarding than studies of man made material and targets.
Lack of appropriate datasets: The available datasets are often insufficient for physical modelling work. There are few polarimetric and interferometric datasets with relevant ground data. The datasets that are available are often limited to few frequencies, and / or to particular times of the year.

Q3: Actions to be undertaken?

1. Identification of specific topics needed in modelling work.
Based on experimental observations and the state of the art in modelling, progress depends on several topics which remain to be solved. A non-exhaustive list might include, for example:
Vertical extinction in tree and forest canopies,
Higher order scattering for soil surfaces,
Polarisation behaviour of microwave measurements of crops,
Phase difference in sea ice

2. Conduct of dedicated experiments
To solve a given topic, dedicated experiments should be conducted making use of one or more of the following: indoor, ground based in-situ, airborne, spaceborne systems, with relevant ground data. Past datasets, often oriented to general modelling purposes, usually did not contain sufficient information to investigate particular crucial points.
 

3. Provision of radar and ground datasets
Funding should be used to set up databases containing relevant radar and ground data  for use by the community. Existing initiatives such as ERA-ORA (EU Network, 1998-2000) should be extended. In particular, there is a need to have ENVISAT datasets adapted to modelling and to the development of retrieval algorithms. Such datasets, with  incidence angle and polarisation diversity,  need to be assembled from different test sites by teams working with the same ground data collection procedures.
 

Presentations:

Digital Elevation Model Generation from SAR Interferometry
Mr Mohammad Halmi Kamaruddin

Modelling of the scattering by a smooth dielectric cylinder: study of the complex scattering matrix using two different models
Laetitia Thirion

On the physical modelling of polarimetric parameters of forests
Dr Thuy Le Toan

Physical interpretation of the sensitivity of polarisation coherence to soil surface roughness
Dr Francesco Mattia

 

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