Sentinel-1 Imaging Performance Verification with TerraSAR-X

This paper presents dedicated analyses of TerraSAR-X data with respect to the Sentinel-1 TOPS imaging mode. First, the analysis of Doppler centroid behaviour for high azimuth steering angles, as occurs in TOPS imaging, is investigated followed by the analysis and compensation of residual scalloping. Finally, the Flexible-Dynamic BAQ (FD-BAQ) raw data compression algorithm is investigated for the first time with real TerraSAR-X data and its performance is compared to state-of-the-art BAQ algorithms. The presented analyses demonstrate the improvements of the new TOPS imaging mode as well as the new FD-BAQ data compression algorithm for SAR image quality in general and in particular for Sentinel-1

Processing of Sliding Spotlight and TOPS SAR Data Using Baseband Azimuth Scaling

This paper presents an efficient phase preserving processor for the focusing of data acquired in sliding spotlight and TOPS (Terrain Observation by Progressive Scans) imaging modes. They share in common a linear variation of the Doppler centroid along the azimuth dimension, which is due to a steering of the antenna (either mechanically or electronically) throughout the data take. Existing approaches for the azimuth processing can become inefficient due to the additional processing to overcome the folding in the focused domain. In this paper a new azimuth scaling approach is presented to perform the azimuth processing, whose kernel is exactly the same for sliding spotlight and TOPS modes. The possibility to use the proposed approach to process ScanSAR data, as well as a discussion concerning staring spotlight, are also included. Simulations with point-targets and real data acquired by TerraSAR-X in sliding spotlight and TOPS modes are used to validate the developed algorithm

Scalloping Correction in TOPS Imaging Mode SAR Data

This paper presents an investigation on scalloping correction in the TOPS imaging mode for SAR systems with electronically steered phased array antennas. A theoretical simulation of the scalloping is performed and two correction methods are introduced. The simulation is based on a general cardinal sine (sinc) antenna model as well as on the TerraSAR-X antenna model. Real TerraSAR-X data acquired over rainforest are used for demonstration and verification of the scalloping simulation and correction. Furthermore a calibration approach taking into account the special TOPS imaging mode properties is introduced

In-Orbit SAR Performance of TerraSAR-X

TerraSAR-X is the first German Radar satellite for scientific and commercial applications. The project is a public-private partnership between DLR and EADS Astrium GmbH. TerraSAR-X consists of a high resolution Synthetic Aperture Radar at X-Band. The radar antenna is based on active phased array technology that allows the control of many different instrument parameters and operational modes (Stripmap, ScanSAR and Spotlight) with various polarizations. Following the TerraSAR-X launch, scheduled for February 2007, it is planned a six month Commissioning Phase covering the characterization and verification of the SAR mission. Within this phase, the Overall SAR System Performance (OSSP) takes care of the correct working and interaction of all SAR system elements essential for obtaining an optimum SAR Performance. The paper covers the first in-orbit characterization and verification results of the SAR system performance for TerraSAR-X operational and experimental modes. This characterization is divided into four phases: Initial Characterization, Scene Characterization –both mostly based on basic and experimental products-, and Verification of TS-X Instrument Command Generation. The different optimization strategies and performance trade-offs are discussed and presented in the paper, including very first TerraSAR-X images. The result of the real SAR data analysis determines the final system baseline and thus the final image quality, e.g. Temperature compensation, Total Zero Doppler Steering, Up/down chirp toggling, transmitted bandwidth, timing interferences, etc. The first section of the paper introduces the activities carried out during the Commissioning Phase for the TerraSAR-X SAR system performance characterization/verification. In the second section, the strategies for the performance optimization and characterization are presented. Finally, the in-orbit SAR performance results are given in section three

Bistatic Experiment Using TerraSAR-X and DLR’s new F-SAR System

A bistatic X-band experiment was successfully performed early November 2007. TerraSAR-X was used as transmitter and DLR’s new airborne radar system F-SAR, which was programmed to acquire data in a quasi-continuous mode to avoid echo window synchronization issues, was used as bistatic receiver. Precise phase and time referencing between both systems, which is essential for obtaining high resolution SAR images, was derived during the bistatic processing. Hardware setup and performance analyses of the bistatic configuration are pre-sented together with first processing results that verify the predicted synchronization and imaging performance

MirrorSAR: An HRWS Add-On for Single-Pass Multi-Baseline SAR Interferometry

This paper reports the Phase A study results of the interferometric extension of the High-Resolution Wide-Swath (HRWS) mission with three MirrorSAR satellites. According to the MirrorSAR concept, small, low cost, transponder-like receive-only satellites without radar signal demodulation, digitization, memory storage, downlink, and synchronization are added to the planned German X-band HRWS mission. The MirrorSAR satellites fly a triple helix orbit in close formation around the HRWS orbit and span multiple single-pass interferometric baselines. A comprehensive system engineering and performance analysis is provided that includes orbit formation, MirrorLink, Doppler steering, antenna pattern and swath design, multi-static echo window timing, SAR performance, height performance and coverage analysis. The overall interferometric system design analysis of Phase A is presented. The predicted performance of the global Digital Elevation Model (DEM) is improved by one order of magnitude compared to presently available global DEM products like the TanDEM-X DEM

Nadir Margins in TerraSAR-X Timing Commanding

This paper presents an analysis and discussion of the Nadir return in the context of radar timing. Results obtained during the Commissioning Phase of TerraSAR-X in verification and measurement of Nadir return and timing margins are shown. Pre-launch assumptions about the Nadir margins were verified and optimized, which led to an improvement in the timing commanding, i.e. a relaxing of the timing. By means of three early acquired TerraSAR-X images which contain Nadir returns their characteristic properties are shown and explained

Hochauflösende Verarbeitung von Radardaten mit synthetischer Apertur

Diese Arbeit stellt das neuartige Frequenz-Skalierungs-Verfahren zur effizienten und genauen Verarbeitung von Spotlight-SAR-Daten ohne Interpolation vor. Es wird eine genaue Modellierung der Spotlight-Abbildungsgeometrie eingeführt. Eine neue analytische Formulierung für SAR-Rohdaten mit Dechirp on Receive-Operation wird abgeleitet. Aufbauend auf dieser Formulierung erfolgt die Entwicklung einer interpolationsfreien Korrektur der Zielentfernungsänderung, der sogenannten Frequenz-Skalierung. Wegen der für alle Ziele gleichen Anfangs- und Endzeitpunkte der Beleuchtung im Spotlight-Modus bietet das SPECAN-Verfahren eine sehr effiziente, aber ungenaue Verarbeitung in Azimut. Eine Azimut-Skalierung wird entwickelt, welche eine hochgenaue und interpolationsfreie Verarbeitung von Spotlight-SAR Daten mit der SPECAN-Methode ermöglicht. Die Verarbeitung von Spotlight-Rohdaten mit Dechirp-Operation in Entfernung erfordert die Erhöhung der Abtastung in Azimut. Zur Vermeidung dieser Erhöhung wird eine Subapertur-Verarbeitung eingeführt. Die hohe Verarbeitungsqualität des Verfahrens wird anhand von simulierten und realen Rohdaten des E-SAR-Sensors des DLR gezeigt. Der Nachweis der Phasentreue wird durchgeführt. Als Anwendungsbeispiel dient ein Spotlight-Interferogramm. Interessante physikalische Besonderheiten des Spotlight-Abbildungsmodus werden durch den Vergleich des Spotlight-Interferogramms mit dem Stripmap-Interferogramm derselben Szene herausgearbeitet

TerraSAR-X Instrument Operations Rooted in the System Engineering and Calibration Project

This paper presents the TerraSAR-X instrument operations embedded into the Instrument Operations and Calibration Segment. Special focus is on the data-take (DT) command generation. The command generation for standard DTs is discussed, and the nonnominal DT commanding is described for several examples which demonstrate the flexibility of both the TerraSAR-X instrument and the instrument operations system on-ground