Abstract
Synthetic Aperture Radar (SAR) is an established remote sensing technique that can robustly provide high-resolution imagery of the Earth’s surface. However, current space-borne SAR systems are limited, as a matter of principle, in achieving high azimuth resolution and a large swath width at the same time. Digital beamforming (DBF) has been identified as a key technology for resolving this limitation and provides various other advantages, such as an improved signal-to-noise ratio (SNR) or the adaptive suppression of radio interference (RFI). Airborne SAR sensors with digital beamforming capabilities are essential tools to research and validate this important technology for later implementation on a satellite. Currently, the Microwaves and Radar Institute of the German Aerospace Center (DLR) is developing a new advanced high-resolution airborne SAR system with digital beamforming capabilities, the so-called DBFSAR, which is planned to supplement its operational F-SAR system in near future. It is operating at X-band and features 12 simultaneous receive and 4 sequential transmit channels with 1.8 GHz bandwidth each, flexible DBF antenna setups and is equipped with a high-precision navigation and positioning unit. This paper aims to present the DBFSAR sensor development, including its radar front-end, its digital back-end, the foreseen DBF antenna configuration and the intended calibration strategy. To analyse the status, performance, and calibration quality of the DBFSAR system, this paper also includes some first in-flight results in interferometric and multi-channel marine configurations. They demonstrate the excellent performance of the DBFSAR system during its first flight campaigns.
Highlights
Synthetic Aperture Radar has evolved in a well-established remote sensing technique that can robustly provide high-resolution imagery of the Earth’s surface independent of weather and daylight conditions
For all flight tests, the existing F-Synthetic Aperture Radar (SAR) antenna carrier together with the older F-SAR antennas were used. This implied a number of limitations with respect to the full potential of the DBFSAR sensor:
Airborne SAR sensors with digital beamforming capabilities are essential tools to prepare such missions, as they allow experimentally establishing the necessary technology for later implementation on a satellite
Summary
Synthetic Aperture Radar has evolved in a well-established remote sensing technique that can robustly provide high-resolution imagery of the Earth’s surface independent of weather and daylight conditions. While the performance of spaceborne SAR systems has significantly evolved over the past decades, their imaging capabilities are still rather limited: conventional SAR is not capable of obtaining both a high resolution and a wide swath at the same time due to principal constraints in the sampling conditions and antenna size [1]. To overcome this fundamental limitation, the past few years have seen intense research activities towards new SAR system designs and architectures that employ one, as in conventional SAR, but multiple digital receive channels. Digital beamforming for transmit and/or receive will solve the contradiction posed by the antenna size in traditional SAR systems that prohibits the SAR sensor from having high azimuth resolution and a large swath width at the same time [2]
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