System status and calibration of the F-SAR airborne SAR instrument

Abstract

The F-SAR airborne SAR instrument represents the successor of the E-SAR system of the German Aerospace Center (DLR), which has been extensively used in the last three decades. Its development was triggered by the current demand for data being simultaneously acquired at different wavelengths and polarisations as well as by the demand for very high resolution in the order of decimetres. F-SAR is a modular development utilising the most modern hardware and commercial off the shelf components. As for E-SAR DLRs Dornier DO228-212 aircraft is the first choice as platform for the new system.Although the F-SAR system is still under development, it is already taking over some of the operational duties of the old E-SAR system. This paper will analyse the performance of the current system, based on the multi-frequency and fully polarimetric imagery acquired during several campaigns in the last two years. Since F-SAR is using a fixed antenna mount without gimbal, precise radiometric calibration is particularly challenging, especially in the shorter wavelengths. Therefore, special emphasis is placed on the system calibration and the associated quality control including the achieved spatial resolution and radiometric accuracy in the different bands.Index Terms-airborne SAR, calibration F-SAR INSTRUMENT DESIGN AND STATUSF-SAR is designed to operate fully polarimetrically at X-, C-, S-, L-and P-bands and will provide single-pass polarimetric interferometric capabilities in X-and S-bands. Repeatpass PolInSAR is a standard measurement mode for the other bands. 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 760MHz effective signal bandwidth at X-band to satisfy the requirement for very high resolution [2]. An overview of the general design parameters can be found in Tab. 1.A special antenna mount was designed to fix planar array antennas to the aircraft. In fully-fledged multi-frequency configuration, it holds seven right-looking dual polarised antennas: three in X-band, one in C-band, two in S-band and one in L-band. The P-band antenna will be mounted under the nose of the aircraft. The antenna mount has the important advantage of making it easy to change the antenna configuration and to mount other antennas without necessitating additional individual airworthiness certification procedures. The nominal antenna configuration provides three single-pass 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 planned [3].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 altitude of the DO228 aircraft. In special applications, other off-nadir angle ranges, such as 60 to 85 degrees for long stand-off ...

Improved airborne PolSAR calibration algorithm based on time-variant attitude compensation

“…With such potential, high-resolution PolSAR systems (Okada et al 2013;Maeda 2013;Janoth et al 2013;Reigber et al 2011) have been rapidly developed in recent years. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden.…”

The Radiometric Measurement Quantity for SAR Images

“…The fractional bandwidth for each channel was still small at below one percent. Several multi-spectral airborne SAR systems exist among which is the F-SAR system from the German Aerospace Center (DLR) [10]. One exemplary scene, which was imaged simultaneously at two different frequency bands, is shown in Fig.…”

Tracking and refocussing of moving targets in multichannel SAR data

“…The GMTI experiments took place in Härkingen (~55 km west of Zurich) and were recorded twice (in 2010 & 2013) with circular flight geometries (see Fig.1) using DLR's F-SAR sensor [5]. Important sensor specifications can be found in the Tab.…”

“…size, intensity and phase of an object. We validate the extended method on data acquired with DLR's F-SAR sensor [5] based on two campaigns covering the same test area conducted in the years 2010 and 2013, flown with circular acquisition geometries. Furthermore, a refocusing of detected moving objects based on the previously extracted trajectories is addressed.…”