Marcus Schwäbisch

Generation of digital elevation models by using SIR-C/X-SAR multifrequency two-pass interferometry: the Etna case study

The authors exploit the interferometric multifrequency potentiality of the SIR-C/X-SAR system which is equipped with an L-, C-, and X-band sensor. They present a solution to improve the unwrapping performance of the C- and X-band data by considering the L-band unwrapped pattern. A new algorithm for the generation of a single digital elevation model (DEM) combining L-, C-, and X-band information is presented. This solution is based on the fusion of the unwrapped phase patterns by using a Kalman filter. The proposed fusion operation also accounts for the coherence characteristics of the three data sets. The selected test site is the Mt. Etna region in Italy which is very interesting from the volcanological and geological point of view. Numerical assessments of the achieved results are provided by evaluating the height accuracy with respect to a reference DEM.

X-SAR interferometry: first results

Repeat-pass interferometry data were acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry at four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model in ground range geometry has been derived. The limitations of the X-SAR interferometry are discussed. >

SIR‐C/X‐SAR multifrequency multipass interferometry: A new tool for geological interpretation

Radar remote sensing is a tool of increasing importance in the study of volcanic sites. Synthetic aperture radar (SAR) is a high-resolution imaging tool used to survey areas which are not practical or safe to be directly inspected. With the introduction of the across-track SAR interferometry (IFSAR) technique, digital elevation models (DEM) can be produced. The usefulness of such interferometric products depends on the ability to extract information that can be used for geological interpretation. We analyzed the shuttle imaging radar C (SIR-C)/X-SAR multifrequency multipass interferometry mission over Mount Etna, Sicily, and we performed a supervised geological interpretation of the coherence maps and a fractal-based analysis of the IFSAR DEMs. The first permits us to recognize different volcanic terrain and to distinguish between vegetated and unvegetated areas, while the second allows us to validate the IFSAR DEMs and to detect large-scale geological features. This latter analysis, performed over the photogrammetric DEM, enabled us to recognize artifacts caused by digitizing and resampling. Obviously, IFSAR DEMs are not affected by these problems. As a consequence, IFSAR products are a valuable aid in geological interpretation.

Comparison of phase unwrapping algorithms for SAR interferograms

The interest in advanced methods of remote sensing has stimulated various investigations on interferometric synthetic aperture radar. The determination of the absolute phase from wrapped phase values has remained a critical step in SAR interferometry. The different approaches to the phase unwrapping problem can be broadly categorized into: integration methods, e.g. the branch-and-cut method, fringe tracking methods, and least-squares (LS) techniques. This paper provides a comparison of the branch-and-cut method and some LS techniques which were recently proposed. In particular, the authors have studied the strategies of both approaches to deal with phase inconsistencies, i.e. phase residues, which are introduced by noise and/or undersampling in SAR interferograms. While the branch-and-cut method deals with phase residues directly by integrating along suitable paths that avoid the crossing of imaginary lines (cut-lines) connecting residues, it is not obvious how LS-techniques are dealing with this problem. The authors illuminate this point and relate the LS approach to the one taken by integration methods. Finally, they draw some conclusions based on their findings.

Operational processing of airborne P-band InSAR data for ground topography estimation

P-band interferometric SAR sensors are currently gaining a wider recognition due to their capability to penetrate vegetation coverage, thus offering the possibility to derive the ground topography of vegetated regions such as forests or agricultural areas. Aerosensings AeS-1 airborne SAR system operates in its P-band mode at 415 MHz with a bandwidth of 70 MHz, providing data with a ground resolution of approximately 3 m. Processing of these data needs particular operations in order to face several effects inherent in the airborne repeat-pass characteristic of the sensor. Subject of this paper is the end-to-end processing chain of AeS-1 data with respect to operational ground topography estimation. Elevation measurements are validated against a high-resolution digital surface model.

Early Results using Single-Pass L-band Pol-InSAR

The extraction of bio-and geophysical parameters by means of Pol-InSAR has gained a lot of interest in recent years. In particular, the exploitation of full quad-pol mode long wave-length (L-and P-band) data in combination with advanced theoretical models like the Random-Volume-over-Ground (RVoG) model has successfully been used to derive quantities like ground topography or tree height with impressive accuracy. However, to date all experiments (airborne and spaceborne) have been conducted in repeat-pass interferometry mode and thus, results have been suffering from two major limitations: temporal decorrelation and, in the airborne case, uncompensated motion errors. Both error sources can significantly reduce the usability of the acquired data, which is of importance especially if operationalmapping of large areas is being considered. This paper reports about first experiments with a single-pass airborne L-band quad-pol interferometer that has been implemented on Intermaps TopoSAR platform.

Accurate focusing of single-pass airborne InSAR data at L-band

Long wavelength airborne single-pass InSAR systems call for very accurate SAR focusing and motion compensation algorithms. We have analyzed 3 different techniques and evaluated their performance using real data acquired with an L-band single-pass interferometer in Canada. Time domain backprojection with terrain-dependent motion compensation shows the best performance with results close to the theoretically expected values.

Comparison of interferometric products of recent high resolution X-band SAR missions and platforms

In the last decade data from high resolution spaceborne X-band systems and airborne InSAR have been made available to the remote sensing community for a wide range of applications. To demonstrate the value of using radar imagery and DEMs from spaceborne systems such as TerraSAR-X, COSMO-SkyMed and SRTM-X, the ortho-rectified radar images and DEMs from Napa Valley, USA, the Bolzano region of the Italian Alps and the Gap region of the French Alps are compared to airborne X-band images and DEMs from the STAR platform of Intermap Technologies. The visual appearance and horizontal accuracy of the radar imagery are compared and examined. The height accuracy and the spatial content of the DEMs from space-borne SAR are also investigated in this paper.

On the survey of volcanic sites: the SIR-C/X-SAR interferometry

Presents an international cooperative study in the field of volcano monitoring by means of SAR interferometry. The case study of the SIR-C/X-SAR mission over Mt. Etna, Sicily, Italy is detailed.