F-SAR: DLRs new advanced airborne SAR system on-board DO228

The Microwaves and Radar Institute of the German Aerospace Center (DLR) is known for its consistent work on the field of airborne synthetic aperture radar and its application. In April 2008 we celebrate the 20th anniversary of the maiden flight of the well-known E-SAR system. E-SAR was maintained well over the time. It provided valuable knowledge to the science community, especially in the last 10 years. However, it became more and more obvious that a technological renewal was inevitable. Consequently the development of a new SAR system was put on the line some years ago under the name F-SAR. This paper will present the current status of the development. I. DLRS NEW AIRBORNE SAR F-SAR identifies the successor of the well-known E-SAR system. The system is under development at the Microwaves and Radar Institute. The development was triggered by the demand for data being simultaneously acquired at different wavelengths and polarisations as well as by the demand for very high range resolution. E-SAR, the old system, cannot comply with these requirements due to technological limitations. F-SAR is a completely new development, utilising most modern hardware and commercial of the shelf components. As for E-SAR DLRs Dornier DO228-212 aircraft is the first choice as platform (see Fig. 1). A. General system design features F-SAR is currently designed to operate in X-, C-, S-, Land P-bands with • simultaneous all polarimetric capability and • single-pass polarimetric interferometric capability in Xand S-bands. Repeat-pass Pol-InSAR is a standard measurement mode. Range resolution is determined by the available system bandwidth. While components limit system bandwidth to 100MHz at P-band, a step-frequency approach is adopted to achieve up to 800MHz effective signal bandwidth at X-band to satisfy the requirement for very high resolution. B. System design overview The F-SAR system comprises a basic system control and data acquisition sub-system to which individual RF subsystem modules are connected. System control is based on an Extended CAN bus and Ethernet concept. This gives the necessary flexibility and the degrees of freedom to configure the system optimally for carrying out the desired measurements and experiments like bistatic SAR for instance. Further, the Fig. 1. Artists view: F-SAR onboard DLR DO228 acquiring data simultaneously in X-, C-, Land P-bands (X-blue, C-green, L-purple, P-red concept makes an extension to any other RF band an easy task (see Fig. 2). A special antenna mount (Fig. 3) designed to fix planar array antennae to the aircraft is under development. Fully-fledged in multi-frequency configuration it holds seven right-looking dual polarised antennae: three in X-band, one in C-band, two in S-band and one in L-band. The P-band antenna is mounted under the nose of the aircraft as indicated in Fig. 1. The antenna mount has the one important advantage that it makes it easy to change antenna configuration and to mount other antennae while avoiding individual airworthiness certification procedures the same time. The nominal antenna configuration provides three singlepass interferometers: across track (XTI) in S-band and X-band, and along track (ATI) in X-band. The mechanical baselines are approx. 1.60m (XTI) and approx. 85cm (ATI). Special configurations, such as a GMTI antenna array in the top frame, are possible. Main F-SAR technical parameters are given in Table 1. For regular Earth observation purposes the radar covers an off-nadir angle range of 25 to 60 degrees at altitudes of up to 6000m above sea level, which is the maximum operating Fig. 2. F-SAR system configuration for multi-frequency and polarimetric operation in X-C-S-L-P-bands including single-pass interferometric capabilities inXand S-bands. Fig. 3. Schematic drawing of the F-SAR antenna mount with the nominal antenna configuration: 3 X-band (blue), 2 Sband (light-blue), C-band (lightgreen), L-band(purple).