L. Sagues

Indoor experiments on polarimetric SAR interferometry

A coherence optimization method, which makes use of polarimetry to enhance the quality of SAR interferograms, has been experimentally tested under laboratory conditions in an anechoic chamber. By carefully selecting the polarization in both images, the resulting interferogram exhibits an improved coherence above the standard HH or VV channel. This higher coherence produces a lower phase variance, thus estimating the underlying topography more accurately. The potential improvement that this technique provides in the generation of digital elevation models (DEM) of non-vegetated natural surfaces has been observed for the first time on some artificial surfaces created with gravel. An experiment on a true outdoor DEM has not been accomplished yet, but the first laboratory results show that the height error for an almost planar surface can be drastically reduced within a wide range of baselines by using the optimization algorithm. This algorithm leads to three possible interferograms associated with statistically independent scattering mechanisms. The phase difference between those interferograms has been employed for extracting the height of vegetation samples. This retrieval technique has been tested on three different samples: maize, rice, and young fir trees. The inverted heights are compared with ground truth for different frequency bands. The estimates are quite variable with frequency, but their complete physical justification is still in progress. Finally, an alternative simplified scheme for the optimization is proposed. The new approach (called polarization subspace method) yields suboptimum results but is more intuitive and has been used for illustrating the working principle of the original optimization algorithm.

Polarimetric radar interferometry for improved mine detection and surface clutter rejection

A recently developed technique, polarimetric radar interferometry, is applied to tackle the problem of the detection of buried objects embedded in surface clutter. An experiment with a fully polarimetric radar in an anechoic chamber has been carried out using different frequency bands and baselines. The processed results show the ability of this technique to detect buried plastic mines and to measure their depth. This technique enables the detection of plastic mines even if their backscatter response is much lower than that of the surface clutter.

Sar Interferometric Coherence in Wide Band Systems

This paper presents a study of the interferometric coherence aimed to the understanding of the main sources of phase error of an operative wide band system. This objective is accomplished by finding a theoretical expression of coherence based on a suitable model capable of including the roughness of the surface, which produces decorrelation besides the conventional spectral overlapping approach. The analysis is validated by means of numerical simulations and controlled experiments in anechoic chamber, with the aim of extrapolating the obtained results to airborne and spaceborne imaging radars.

BURIED MINE DETECTION BY POLARIMETRIC RADAR INTERFEROMETRY

In this paper we have presented a new polarimetric and interferometric approach that can be applied to improve the sub-clutter visibility in de-mining applications. The obtained experimental results have shown that buried plastic mines can not be detected by using only SAR images. However, after applying the method presented here, it is possible to separate the scattering mechanism that is associated with the clutter surface from that corresponding to the mine and estimate their height location. Nevertheless, the success of the proposed method will depend on the geometry of the problem. Indeed, it is necessary the surface clutter to be physically separated from the mine in order to distinguish both scattering mechanisms by optimising the interferometric coherence.

Experimental comparison of different scattering mechanism selections for vegetation height retrieval by POLINT

The application of polarimetric radar interferometry to the estimation of vegetation height is studied. A comparison between different choices for the scattering mechanisms employed in the retrieval algorithm is presented. When applied to crops, the best results are derived from the height difference between interferograms generated at HH+VV and HH-VV polarizations.

Laboratory experiments of polarimetric radar interferometry: DEM generation and vegetation height estimation

A coherence optimization method, which makes use of polarimetry to enhance the quality of the interferograms, has been experimentally tested under laboratory conditions in an anechoic chamber. The experiments have proved the remarkable contribution that this technique offers in two important applications: the improvement of digital elevation maps (DEM) generation and the estimation of the height of vegetation targets.

Crop height monitoring and surface parameter estimating using polarimetric and interferometric radar techniques

The paper presents different polarimetric and interferometric inversion radar approaches to extract the characteristics of vegetation and bare soil surfaces. The electromagnetic waves interactions with scatterers in a random medium are a complex process, which is sensitive to a much larger number of target parameters. Consequently, the estimation of surface and vegetation parameters can not be achieved by using fixed polarization single frequency interferometric SAR data, even when a simple homogeneous one-layer model is considered. In this way, some multibaseline SAR interferometric inversion algorithms have been proposed in order to extend the number of independent parameters. However, these models are based on the first-order scattering approximation, ignoring the effect of multiple scattering. The introduction of polarimetry provides an important tool to minimize multiple scattering effects by selecting the optimum scattering mechanisms, making parameter estimation more robust. Some indoor and outdoor measurements have been carried out to test these inversion techniques. The measurements have been conducted on bare rough surfaces and sorghum fields at different growth stages with a very accurate gound-truth. The results are compared to those obtained by applying other existing techniques, such as the Frecuency Correlation Function (FCF) and empirical inversion methods.

Extraction of vegetation structure and surface parameters using polarimetric and interferometric SAR techniques

Presents different polarimetric and interferometric inversion radar approaches to extract the characteristics of vegetation and bare soil surfaces. The inversion techniques presented make use of multifrequency, radar interferometric and polarimetric data to increase the number of input data. The proposed techniques have been experimentally tested under laboratory conditions as well as in real outdoor scenarios.

Wide Band Polarimetric Interferometry for DEM Improvement and Retrieval of Vegetation Height

The Interferometric coherence can be optimised by properly using polarimetric information. The optimisation method has been experimentally tested under laboratory conditions in an anechoic chamber. The experiments have proved the remarkable contribution that this technique offers in two important applications of SAR interferometry: the improvement of Digital Elevation Models (DEW) generation and the estimation of vegetation height.