Change detection in sequences of SAR sub-aperture images

Abstract

In the last few years, image acquisition modes have been developed for spaceborne SAR systems aiming on an enhancement of geometric resolution. This offers new opportunities for the calculation of so-called sub-aperture images and their analysis. Due to the increase of illumination time, one single image can be subdivided into multiple subapertures, which are temporarily closely arranged to each other with a lower geometric resolution than the original image. Focusing on this increase of illumination time, the Staring Spotlight (ST) mode of the German TerraSAR-X (TSX) and TanDEM-X (TDX) satellite constellation is mentionable. Here, the azimuth bandwidth can be divided into subset images, in which e.g. vehicles or ships are still well observable. Consequently, moving targets can be detected without utilizing SAR raw data. For this, only a Single Look Complex (SLC) image has to be considered. In this study, different stacks consisting of sub-aperture images are calculated, which are used for incoherent change detection. The detection is performed as an adaption of a method for change analysis in SAR time series data developed earlier. This method comprises the detailed description of changes, concerning their categorization and classification. Therefore, suitable features have to be calculated leading to a clear distinction of different change categories. As test data, TSX SLC images are used which were acquired both in ST and in High Resolution Spotlight (HS) mode. An assessment concerning their suitability for the incoherent change detection method applied to the sub-apertures is given. With future studies, it will be tested, whether the temporal aspect can be meaningfully regarded for the change categorization step. For this, the concept of so-called high activity objects, which were the basis of the earlier developed change analysis scheme, might be of relevance for the analysis of changes in sub-aperture sequences.