No abstract

FIgURE 3. Forest height maps derived from model-based inversion of polarimetric SAR interferometric (Pol-InSAR) data acquired by DLR's airborne SAR system over the Traunstein forest located in Germany from 2003-2013 [36]. In 2008 the acquisitions where performed during wet (rain) and dry conditions (indicated by the cloud and sun pictogram) and in 2009 in leaves-on and leaves-off conditions (indicated by the leaves-on and leaves-off pictogram) -in all cases leading practically to the same height estimates. The reference map (for 2003) derived by airborne lidar data is shown in the lower left corner.

No abstract

Tandem-L is proposed as a spaceborne SAR mission developed and operated by the German Aerospace Center in cooperation with several Helmholtz research centers and the German space industries. The mission concept comprises two fully polarimetric radar satellites providing mono-and bi-static SAR imagery. A key feature of these SAR sensors is the employment of large lightweight unfurlable mesh reflectors fed by digital feed arrays. The main advantage of this new SAR system concept is the provision of large antenna apertures in space and flexible operation via reconfigurable feed electronics. By this, it becomes possible to map, for the first time, a continuous 350 km wide swath with 7 m azimuth resolution with excellent noise equivalent sigma zero (NESZ) and ambiguity suppression. This paper shall give an overview on the technical aspects of the Tandem-L SAR instrument and antenna design. In particular, after a short review of the SAR system requirements, the concept of reflector SAR systems is outlined and the operation principle is presented. General guidelines for the design of array-fed reflector antennas with application to SAR imaging are given. Then the optimization approach of the feed array design is detailed, with specific emphasis on a fixed beamforming concept in azimuth. In this context also the problem of cross-pol pattern mitigation is addressed. These optimization steps are shown to be crucial for achieving the performance requirements in quadpol acquisitions. Beamforming in elevation is performed on board the spacecraft via digital hardware. This paper presents the beamforming architecture on receive for Tandem-L, which would apply in general for instance also to planar multi-elevation beam SAR antennas with Scan-On-Receive capabilities. Tandem-L is operated as a staggered SAR, which means varying the pulse repetition interval from pulse to pulse. In this context the major design challenges are presented. Moreover, the impact of pulse staggering on the imaging performance is discussed. Tandem-L's SAR performance is presented by means of numerical simulations showing that the performance requirements imposed by the scientific user community could be met. The final part of the paper addresses options for high azimuth resolution imaging as well as a beamforming method for enhanced range ambiguity suppression.

No abstract