Performance Analysis of Spaceborne SAR Vehicle Detection an Velocity Estimation

Field: Computer Science (Physical Sciences)

Remote Sensing Technology Institute, German Aerospace Center (DLR), Oberpfaffenhofen, D - 82234 Wessling, GermanyCommission III/5KEY WORDS: Trafﬁc Monitoring, SAR, Satellite ImagesABSTRACT:With TerraSAR-X and RADARSAT-2, two dual-channel SAR satellites will belaunched in the next months. Both sensors allow fordetecting moving objects, and, by this, enable trafﬁc monitoring from spac e. This paper revises the theoretical background of trafﬁcmonitoring with space-based SARs and presents concepts for the TerraSAR-X trafﬁc monitoring system. Compared to previous workan extensive analytical and empirical accuracy analysis is included for both vehicle detection and velocity estimation. The accuracyanalysis includes a theoretical accuracy evaluation and a validation with real data.1 INTRODUCTIONSince the launch of new optical satellite systems, e.g. Ikonos andQuickBird, satellite imagery with 1-meter resolution or higher iscommercially available and a number of approaches have beendeveloped to detect or track vehicles in this imagery (see e.g. ref-erences in (Leitloff et al., 2005)). Trafﬁc monitoring based onoptical satellite systems, however, is only possible at daytime andcloud-free conditions. Two high-resolution Spaceborne RADARsystems, TerraSAR-X (Germany) and RADARSAT-2 (Canada),which will be launched this year will overcome this limitations.Yet there are other difﬁculties inherent in the SAR imaging pro-cess that must be solved to design a reasonably good approachfor trafﬁc monitoring using spaceborne Radar.The task of detecting moving vehicles with SAR sensors (groundmoving target indication (GMTI)) has been addressed in severalscientiﬁc publications. The method of choice in GMTI is to use aRadar or SAR sensor with at least 3 channels and use space-timeadaptive processing (STAP) for target detection. Further refer-ence to that topic can be found e.g. in (Klemm, 1998, Living-stone et al., 2002, Gierull, 2004). Unfortunately, civilian spaceborne SAR systems with 3 or more channels are currently notavailable. The upcoming TerraSAR-X mission as well as theCanadian RADARSAT-2 mission will be equipped with a singlechannel SAR that can be switched to an experimental mode withtwo channels to enable along-track interferometric applicationslike trafﬁc monitoring. Although the use of a 2-channel systemis not optimal for detecting vehicles, some methods exist that al-low detection under certain conditions. The classical approach todo so is to use the displaced phase center array (DPCA) method.Along-track interferometry (ATI) is another method that can beused. The issue of detecting moving targets using ATI is for in-stance discussed in (Gierull, 2001, Sikaneta and Gierull, 2005).In (Gierull, 2002) special emphasis is put on the probability den-sity functions associated with this detection. The inﬂuence ofvehicle acceleration is discussed in (Sharma et al., 2006). Trafﬁcmonitoring from space is quite rare so far. But as shown in (Breitet al., 2003, Meyer and Hinz, 2004, Meyer et al., 2005) ﬁrst en-deavors have already been carried out.Based on a revision of the effects of moving objects in SAR Datawe present a concept of detection and velocity estimation of vehi-cles, thereby considering the restrictions of civilian SAR satellitesystems. The main focus of this paper, ﬁnally, lies on the perfor-mance characterization of the main components of this concept,in order to predict and validate the expected results of the systemfor TerraSAR-X. The performance analysis includes both a the-oretical accuracy evaluation and a validation with real airborneSAR data.2 MOVING OBJECTS IN SPACEBORNE SAR IMAGESBefore outlining the concepts for vehicle detection and veloc-ity estimation we brieﬂy summarize the effects of moving ob-jects in spaceborne SAR images. Here, only the resulting formu-lae are included; a derivation of the formulae can be found, e.g.in (Meyer et al., 2005), while a comprehensive overview on SARimage processing is given in (Cumming and Wong, 2005).2.1 Object Motion Effects in SAR — A SummaryThe position of a Radar transmitter on board a satellite is givenby P