ACTIVE MICROWAVES
D. Evans (1) and D. Vidal-Madjar (2)
(1) JPL Pasadena, California (U.S.A.)
(2) CNRS/CRPE, Vélizy (France)
1 - PLENARY SESSION
The plenary session of topic 3 addressed, through 4 papers, the main subject of research of this few last years.
The first paper (Ulaby et al., presented by J.D. Wall from JPL) intended to demonstrate that the radar
remote sensing is now entering the era of applications. It has been shown that, using multi-parameter
measurements and some new mathematical tools for classification, it is possible to derive, at least for the
training site, numerous interesting parameters : tree species, soil water content for example.
The second paper (Pratti and Rocca, given by Pratti) has shown the potential of the SAR phase analysis
which is now possible, using the ERS-1 SAR. Through interferometric techniques, it is possible to derive
topographic maps with the advantage over the optical remote sensing of not being perturbed by the weather. It is
also possible to detect very small changes of the topography leading to a powerful tool for tectonic studies.
Finally, working with geometrical effects on wavelengths ground projection, the authors described how it is
possible using two different images of the same region to improve the spatial resolution.
Laver gnat and Vidal Madjar (presented by Vidal-Madjar) presented some reflections on the coupling of
active and passive techniques. The physical basis of the synergy is the relation which exists between the
directional albedo and the emissivity. It has been shown that, provided one has a validated model or
measurements of the bididrectional scattering coefficients, it is possible to link the radiative temperature to
backscattering. As an example of what can be done today from space, three instruments of ERS-1 (radar
altimeter, microwave sounder and ATSR) have been presented to show how their combined use can improve the
derivation of atmospheric and surface parameters.
Finally a paper was presented dealing with one of the major problem in experimental physics : the
calibration of the power measurement for a radar (Ottl et al., presented by Ottl). This paper has shown that if
careful experiments are implemented using corner reflectors, it is possible to achieve a very accurate absolute
calibration, better than 1 dB. They also showed that the same approach is able to derive more accurate
instrumental characteristics like, for example, the azimuth antenna pattern. Some results have been presented
through analysis of airborne and space borne radar calibration campaigns.
2 - POSTER SESSIONS
The papers presorted during the poster sessions dealt with some of the topics presented by the keynote papers.
Several papers addressed the application of interferometric analysis. Mansonet et al. have shown the
possibility to detect flows in glaciers by comparing the phases of two ERS-1 images. T. Farr et al. presented the
TOPSAR project, based on two linked satellites, designed to derive global topography using this technique. But
several studies have to be pursued to be able to correctly interpret the small variations of the phase. This is the
main interest of the paper presented by Lefort et al. which described an experiment designed to look at the
dependence of the phase relationship cm soil wetness for bare soils.
But most of the papers were dealing with physical modeling and comparisons with experiments. These
papers were essentially interested in the analysis of multiparameter radar measurements (multi-incidence angles,
frequencies, and polarization). E. Rignot et al. presented observations of the Greenland ice sheet based on
multifrequency and multipolanmetric SAR data. Interesting results were presented for crops and bare soils
(Lorich et al. and Rakotoarivony et al.) showing that the optimistic presentation of Ulaby et al. plenary paper
may not be realizable everywhere. Despite the difficulties to build a comprehensive modeling of the microwave
interaction with land surface, Prevot and Schmugge presented an interesting way to use model to simulate a data
base which can be used to derive simple retrieval algorithms.
The paper by Wall described the aerodynamic surface roughness derivation from a multi-parameter
radar signal.
An original approach of space observations is discussed by Magayi and Kerr. It is concerned by the use
of the ERS-1 wind scatterometer which is simply a coarse resolution imaging radar. The data acquired during
