An X-Band Airborne DInSAR Experiment With the OrbiSAR System
Stefano Perna(1), Christian Wimmer(2), Joao Moreira(3) and Gianfranco Fornaro(4)
(1) Università degli Studi di Napoli, Via Medina 40, 80133 Napoli, Italy
(2) Wimmer Consulting, Rosemeyerstr. 24, Ergoldsbach, Germany
(3) Orbisat S.A., Av. José de Souza Campos 1815, Campinas (SP), Brazil
(4) IREA-CNR, Via Diocleziano 328, 80124 Napoli, Italy
Differential SAR Interferometry (DInSAR) carried out by means of repeat pass satellite data is today a well established technique which allows monitoring ground deformation to a millimetric accuracy. Notwithstanding, the use of spaceborne SAR sensors for the application of this DInSAR technique implies some limitations.
First of all, orbits covered by satellites do not allow achieving high accuracy in monitoring ground deformation components in North-South direction. Secondly, the interferometric revisiting time, i.e., the time after which the same region is imaged from similar view angles, cannot be changed in case of emergency and, more important, even for the new generation of satellite sensors, it doesn’t allow daily (or hourly) deformation monitoring.
Use of airborne platforms could allow overcoming such limitations, thus making it possible to achieve higher operative flexibility compared to spaceborne platforms. In addition to this, airborne SAR systems provide in general higher spatial resolutions.
Unfortunately, in contrast to the satellite case, interferometric processing of repeat pass airborne SAR data is in general a much harder task.
This is first of all due to the fact that, in contrast to the satellite case, airborne SAR data focusing requires precise knowledge of both sensor position and topographic profile of the illuminated area; accordingly, inaccuracies of the available DEM and of the Motion Sensing System (MSS) mounted onboard the aircraft could be responsible for amplitude and phase aberrations in final airborne SAR images -. Moreover, efficient airborne SAR data focusing requires the application of approximations  which may impair the accuracy of focused image even if DEM and MSS inaccuracies are absent. Aberrations induced on focused airborne data by MSS and/or DEM inaccuracies, as well as by approximations carried out during the focusing step are commonly referred to as residual errors in the literature.
Residual errors are critical especially in repeat pass airborne interferometry because they may be significantly different in the two channels and may thus lead to major differential aberrations in the final interferogram.
Possible solutions aimed at limiting - or estimating , differential residual errors affecting airborne repeat pass interferograms have recently been proposed. Moreover, they have been applied to C/L-Band data acquired in several missions carried out in the last years - , thus making it possible the generation of airborne C/L-Band DInSAR time series.
On the contrary, a very small number of X-Band missions have recently been planned, due to the fact that uncompensated residual errors in this case are more critical if compared to the wavelength, thus rendering more difficult the generation of accurate DInSAR interferograms .
In this paper we show the results of an airborne DInSAR X-band experiment carried out over the Perugia area, center of Italy, by using the OrbiSAR system . Eleven repeated passes were carried out in two days; two corner reflectors were deployed on the ground in a hilly region, and one corner reflector was vertically moved between the two days.
We first of all perform an analysis of the obtained DInSAR interferograms for a region 2 Km by 4 Km wide. Moreover, we show measurements carried out on corners reflectors, in order to evaluate the system detection capability.
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Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,