PREPRINT The Legacy of the SIR-C/X-SAR radar system: 25 years on Anthony Freeman1,*, Manfred Zink2, Ed Caro1, Alberto Moreira2, Louise Veilleux1, Marian Werner2 1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA 2. DLR, German Aerospace Center, Microwaves and Radar Institute, 82234 Oberpfaffenhofen, Germany *Corresponding author: Tel: +1 (818) 354 1887 e-mails:
[email protected] (A. Freeman);
[email protected] (M. Zink);
[email protected] (E. Caro);
[email protected] (A. Moreira);
[email protected] (L. Veilleux);
[email protected] (M. Werner) Abstract Twenty-five years ago, the two flights of the SIR-C/X-SAR Synthetic Aperture Radar (SAR) system on the Space Shuttle Endeavour blazed a trail toward the future with a series of radar system innovations - that nearly every spaceborne SAR flown since then has benefited from, and in some cases improved upon. Many of the SAR techniques adopted by SAR system designers worldwide as part of their toolkit, such as: ScanSAR, Spotlight mode, along-track interferometry, polarization diversity and polarimetry, polarimetric calibration, variable length and bandwidth pulses, and on- board processing, can trace their heritage back to this first-of-a-kind, civil-use SAR system. The electronic steering capability of SIR-C’s phased array antenna, combined with the exquisite orbit track control provided by the Space Shuttle, paved the way for systematic mapping of the Earth’s topography by the Shuttle Radar Topography Mission, and later by TanDEM-X. Some techniques, such as multi-frequency SAR, multi-frequency repeat-pass interferometry and onboard processing have yet to be fully exploited.