Michael Ludwig

Technology developments for the next generation of spaceborne SAR instruments based on digital beamforming

During the past ten years a number of research groups around the world have been investigating the use of digital beamforming for spaceborne SAR instruments. The separate optimization of the effective transmit and receive aperture sizes together with the splitting of the receive side into multiple receive sub-apertures which can be combined on board by means of digital beamforming allows for a number of new SAR modes. With this it is for example possible to overcome the principle swath width and azimuth resolution limitation known in classical SAR instrument designs. ESA has performed and initiated a number of systems studies to identify the critical technologies needed for this type of instrument. Based on these system studies a number of technology development activities have been started. This paper gives an overview on the studies and technology developments performed in this context.

Modelling and analysis of rain effect on Ka-band single pass InSAR Performance

The adoption of Ka-band for performing SAR interferometry is considered very promising since it could provide the possibility to embark the full instrument within a single satellite. However, one of the major concerns of the effectiveness of spaceborne Ka-band radars is the impact of the atmosphere, and, in particular of precipitation on the instrument performance and availability. This paper analyzes the impact of precipitation on the performance of Ka-band across-track InSAR. In order to assess the rain impact on the InSAR random height error, the paper proposes an extended form of the interferogram coherence. The paper shows that, for the reference instrument configuration investigated, a random height error compatible with HRTI-3 specification can be met under moderate rain condition.

Digital beam forming for C-Band SAR and technological elements

ESA has initiated several studies to enhance the performance of next generation of C-Band SAR. This paper provides an overview of the on-going demonstration activity for critical technology in C-band as required for a next generation Sentinel-1 SAR instrument with enhanced performance in terms of coverage and resolution. The new instrument will use digital beam forming (DBF) capabilities to achieve the performance improvement by a new combined analogue/digital beam forming unit called TRIM (Transmit/Receive Interface Module). The paper reports on the status of ongoing developments at subsystem level including required technological elements as European GaN and deep sub-micron silicon semiconductor technology.

Ka-band SAR interferometer

In the frame of the “Study into Ka-band SAR”, a project funded by the European Space Agency (ESA), the authors investigated new instrument concepts to implement a spaceborne high resolution interferometric SAR operating at Ka-band. In particular, thanks to the antenna separation which is required at these frequencies to achieve accurate height measurements, the analysis was focused on concepts related to single pass interferometry from a single platform. This paper illustrates the definition of the instrument concepts elaborated during the Study, gives an insight of the performance that they are capable to achieve and lays the foundations for the preparation of the roadmap that will conclude the Study paving the way for possible future developments.

Design and performance of a spaceborne Ka-band interferometrie SAR antenna system

This paper presents the design and performance of a spaceborne interferometrie SAR antenna operating in Ka-band. The bi-static instrument is a single pass across-track interferometer SAR based on one transmit antenna able to scan 8 off nadir beams and two distant receive antennas using scan-on receive techniques to ensure the overall radar link budget.

Miniaturized altimeter an innovative concept of miniaturized altimeter for constellations

Current dual frequency altimeter designs with a SAR mode such as the SRAL altimeter on-board Sentinel 3 have a mass of around 60 kg and a mode dependent power consumption of 90 to 100 Watts. These are typical figures for state-of-the-art instruments of this kind. However, for a potential constellation of altimeters aiming at improving temporal and spatial coverage, the mass and the power consumption need to be drastically reduced in order to be compatible with cost effective micro-satellites that can accommodate around 40/50kg & 50/100W for the whole altimetry payload (altimeter, radiometer, POD GNSS receiver and laser reflector). Starting from these objectives, the study of a miniaturized altimeter operating in Ku-band and C-band (for ionosphere delay correction) with a combined radiometer-altimeter antenna was performed by Thales Alenia Space in the frame of two ESA contracts (one for the instrument and electronics design and one for the antenna). This study is an extensive and innovative reconsideration of the altimeter design, taking into account all the technical and technological possibilities to achieve the challenge of keeping high altimetry performances while targeting a drastic reduction of volume, of mass, of telemetry rate and especially of power consumption (identified as the main issue), assuming an altimetry mission operational at the horizon of 2020.