Madhukar Chandra

Potential of coherent decompositions in SAR polarimetry and interferometry

A comparative study has indicated that coherent decompositions may have high potential in applications using fully polarimetric and interferometric SAR data, as an alternative or supplement to standard non-coherent techniques developed during the last decade. One important reason for this seems to be that the coherent techniques are better able to benefit from the coherent nature of the underlying data and scattering mechanisms. By avoiding averaging at the first processing stage, the coherent techniques can extract target features that may otherwise be lost in the early averaging process. On the other hand, averaging is indeed important in most cases for obtaining stable and reliable end results.

Analysis of Atmospheric Propagation Effects in TerraSAR-X Images

TerraSAR-X, the first civil German synthetic aperture radar (SAR) satellite has been successfully launched in 2007, June 15th. After 4.5 days the first processed image has been obtained. The overall quality of the image was outstanding, however, suspicious features could be identified which showed precipitation related signatures. These rain-cell signatures motivated a further in-depth study of the physical background of the related propagation effects. During the commissioning phase, a total of 12000 scenes have been investigated for potential propagation effects and about 100 scenes have revealed atmospheric effects to a visible extent. An interesting case of a data acquisition over New York will be presented which shows typical rain-cell signatures and the SAR image will be compared with weather-radar data acquired nearly simultaneously (within the same minute). Furthermore, in this contribution we discuss the influence of the atmosphere (troposphere) on the external calibration (XCAL) of TerraSAR-X. By acquiring simultaneous weather-radar data over the test-site and the SAR-acquisition it was possibleto improve the absolute calibration constant by 0.15 dB.

Combined application of target decomposition methods and polarimetric SAR interferometry: some preliminary results

The application of interferometric techniques to polarimetric SAR data is a relative new and promising research field. Noteworthy examples of its potential have been reported by Cloude and Papathanassiou for the retrieval of forests height. In general, polarimetric analysis approaches have been considered for optimizing the interferometric coherence, mainly in order to improve the generation of digital elevation models. In this paper, we will present the first results that we obtained by combining interferometric analysis with coherent target decomposition methods (in particular, the one proposed by Krogager); the different coherence properties of target models will be investigated and a provisional evaluation of the usefulness of this approach will be given.

Comparison of precipitation effects in space-borne X- and Ka-band SAR imaging

As the operating frequencies of SAR-systems are increasing, the visible distortions due to precipitation in SAR-images are becoming more frequent. This holds especially for the case of convective rain events. The German space-borne satellite TerraSAR-X has delivered a series of measurement examples, which were used to study precipitation effects in SARimages. Based on these valuable data takes and simultaneous weather radar measurements, a quantitative estimation of precipitation effects in SAR-images is presented. In a further step, an attempt is made to extrapolate the observed effects to systems operating at higher nominal frequency-bands, i.e. Ka-band, being taken under consideration for future SARsystems.

Improving SAR data processing with polarimetric reference functions in the range Doppler algorithm

ABSTRACT Synthetic aperture radar (SAR) is a form of radar that can be used to create images of objects and landscapes. The main important application of the polarimetric SAR can be found in surface and target decomposition process of its image processing. In this article, we propose a method of polarimetric SAR data processing using two new polarimetric reference functions of canonical targets with the intention to apply in coherent decompositions. Our experiment uses polarimetric backscatter characteristics of the dihedral and trihedral reflectors as the targets under a ground-based SAR geometry to create the polarimetric reference functions for azimuth compression in the SAR data processing. We process the data using Pauli decomposition to investigate the effect of our functions on the RGB (red, green, and blue) properties of the processed images. The results show that Pauli decomposition using our functions produces images with different distribution and intensity of RGB colours in the image pixels with some signs of improvement over the traditional range Doppler algorithm. This demonstrates that our polarimetric reference function can be used in the decomposition steps of the traditional SAR data processing and can potentially be used to reveal some useful quantitative physical information of target points of interest and improve image and surface classification.

RCS measurements under GB-SAR environment

In this paper, the pyramidal horn antenna has been considered and used in a measurment system that has been developed by using the principle of the ground-based Synthetic Aperture Radar (GB-SAR) system. Results of experimental data by means of a GB-SAR system operating at C band, devoted to the measurment and the characteristics of the radar cross section (RCS) of the canonical targets, such as flat plate, dihedral and trihedral corner reflectors, that represented the structure of the land and urban, are reported.

Soil parameter estimation and analysis of bistatic scattering X-band controlled measurements

In this paper, we will present well controlled experimental bistatic X-band measurements of rough surfaces, which have been recorded in the Bistatic Measurement Facility (BMF) at the DLR Oberpfaffenhofen, Microwaves and Radar Institute. The bistatic measurement sets are composed of soils with different statistical roughness and different moistures controlled by a TDR (Time Domain Reflectivity) system. The BMF has been calibrated using the Isolated Antenna Calibration Technique (IACT). The validation of the calibration was achieved by measuring the reflectivity of fresh water. In the second part, the first validation of the specular algorithm by estimating the soil moisture of two surfaces with different roughness scales will be reported. Additionally, a new technique using the coherent term of the Integral Equation Method (IEM) to estimate the soil roughness will be presented, as well as evaluation of the sensitivity of phase and reflectivity with regard to moisture variation in the specular direction.