Antoni Broquetas

Calibration requirements for airborne SAR interferometry

One of the main limitations on the use of SAR interferometry to automatically generate Digital Elevation Models (DEM) is related with both the accurate calibration of the system parameters and its stability from flight to flight. The unstable movements of an airborne SAR platform can be corrected during the processing step, as long as those movements are recorded in an accurate manner. Errors and time drifts in the system parameters or on the plane position and attitude measurements lead to geolocation errors in the final DEM. A calibration method based on the so-called “sensitivity equations”, which relate the target location error with the error on the estimation of the system parameters, is described. The equations have been derived by differentiating the interferometric geolocation equations in closed form for the most general case in a squinted geometry. The interferometer parameters considered are the baseline length and elevation, common time delay, interferometric constant phase, plane position and attitude angle offsets, etc. The equations can be used to both calibrate a single DEM from different ground control points (GCP) spread along the swath and the frill interferometer from well-known located comer reflectors (CR).

Sensitivity equations and calibration requirements on airborne interferometry

The usage of an airborne interferometric SAR to mass map production is strongly dependent on the capability of performing the data processing in a near automatic mode. One of the main limitations is related to both the accurate calibration of the system parameters, its stability from flight to flight and the correct in-flight recording of aircraft position and attitude. The unstable movements of an airborne SAR platform, if recorded in an accurate manner, can be corrected during the processing step. Measurement errors and time drifts lead to location errors in the final DEM. The system requirements in both accuracy and stability to fulfil a quality-mapping requirement can be resolved from the sensitivity equations. The same equations can be also used to calibrate the system parameters from the location errors on the imaging of well-known targets, usually corner reflectors.

Geocoding techniques for interferometric and polarimetric airborne SAR data

This paper presents a detailed study of geocoding algorithms for interferometric SAR data from airborne sensors. They allow to relate a phase value in slant-range coordinates to a position in a cartesian reference system and, hence, a height value on a topographic map. Two basic approaches, which follow forward or backward strategies, are proposed in this paper. Another aspect is related to the kind of the acquisition mode: single- or repeat-pass. In general, a wide variety of techniques and combinations (single or repeat pass, direct or indirect transformations, one or two steps, zero-Doppler or squinted geometry) exist. This paper reviews the state-of-the-art of these combinations, as well as their evaluation, comparison and discussion by means of real data from the DLR’s E-SAR system. The discussion includes the problem of polarimetric data geocoding. In that case, the map-projected height information derived from a X-band single-pass system is used to geocode non-interferometric channels (for example polarimetric L-band data).

Database of "In Vivo" Measurements for Quantitative Microwave Imaging and Reconstruction Algorithms

Reconstruction algorithms and equipment have been developed for microwave imaging, with emphasis on noninvasive control of deep hyperthermia treatments. Tomographic reconstruction algorithms have also been developed for qualitative spectral and quantitative spatial iterations. The data can be accessed from the e-mail address ftp voltor.upc.es.

Calibration of interferometric airborne SAR images using a multisquint processing approach

This paper presents a technique to calibrate interferometric airborne SAR images based on a multisquint processing approach, i.e., by processing the same image pairs with different squint angles we can combine the interferograms to obtain the desired phase correction. Airborne single-pass interferometric data from the DLRs E-SAR is used to validate the method.

Phase statistics and quality evaluation of deformation maps with multiple-image differential interferometry

This paper presents a closed formulation to evaluate the quality of terrain deformation maps obtained with multi-image differential interferometry. The analytical formulation, based on the application of the asymptotic covariance matrix, that propagates the interferogram coherences to the linear deformation and DEM error accuracies when using a stack of interferograms, is developed and validated with real data from the ERS satellites.

Generation of precise wide-area geocoded elevation models with ERS SAR data

The authors present an improved technique for the generation of digital elevation models (DEM), capable of dealing with full scene images (100/spl times/100 km) coming from an interferogram obtained with ERS satellite data. Starting from an interferometric processor aimed to the geocoding of smaller areas, now the authors expound the new improvements based on the use of ground control points (GCP) in order to calibrate some imprecisions which appear in the case of very wide swaths. A generated DEM of the test zone of Tarragona (Spain) and its error assessment are presented.

Efficient detection and correction of residual motion errors in airborne SAR interferometry

This paper discusses the detection and correction of residual motion errors in airborne SAR interferograms. They usually appear due to the lack of precision in the navigation system. Two techniques existing in the literature to detect such errors are presented, highlighting differences and similarities. The effects of residual motion errors in the final interferogram are mainly two: azimuth phase undulations and azimuth registration errors. A new correction approach is proposed, which corrects both effects in one step, avoiding the use of interpolations. Additionally, the spectral diversity technique, used to estimate registration errors, is critically analyzed. Airborne L-band repeat-pass interferometric data of the German Aerospace Center (DLR) experimental airborne SAR (E-SAR) is used to validate the method.

Electromagnetic scattering measurements on a fractal surface

In this paper we present a procedure devoted to validate innovative theories on the electromagnetic scattering from natural surfaces, using fractal functions for the surface description. A fractal surface has been built as a superposition of cardboard and aluminium layers, according with a computer design based on the Weierstrass-Mandelbrot (WM) fractal function. Its statistical properties have been verified with optical measurements. The electromagnetic field scattered at X band from the built surface has been measured in controlled environment as a function of the incidence angle. Obtained results have been compared with those of the Kirchhoff Approximation (KA) and the Small Perturbation Method (SPM) in conjunction with the fractional Brownian motion (fBm). Congruence and discrepancies of measured data with theoretical results are discussed, providing a validation of the methods

A mosaic technique for the generation of wide-area DEMs with interferometric SAR data

We propose and evaluate an operational algorithm, capable of obtaining a mosaic DEM from a wide area from several interferometric data sets.