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SIR-C/X-SAR (Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar) is a joint project of the National Aeronautics and Space Administration (NASA), the German Space Agency (DARA) and the Italian Space Agency (ASI). Data are collected in L-Band and C-Band by SIR-C, and X-Band by X-SAR. An imaging radar system launched aboard the NASA Space Shuttle twice in 1994,. SIR-C/X-SAR's unique contributions to Earth observation and monitoring are its capability to measure, from space, the radar signature of the surface at three different wavelengths and make measurements for different polarizations at two of those wavelengths. SIR-C image data will help scientists understand the physics behind some of the phenomena seen in radar images at just one wavelength/polarization, such as those produced by SeaSAT. Investigators on the SIR-C/X-SAR Science team will use the radar image data to make measurements of: Vegetation type, extent and deforestation; Soil moisture content; Ocean dynamics, wave and surface wind speeds and directions; Volcanism and tectonic activity; Soil erosion and desertification.

Mission Summary

The SIR-C/X-SAR is an imaging radar system flown aboard the space shuttle with two flights from 9 to 20 April 1994 and 30 September to 11 October 1994. Flying at an altitude of 215 km in a circular orbit and a 57 degree inclination, the three-frequency, multipolarization radar performs a variety of Earth environmental observations that will improve our understanding of the Earth's carbon, water, and energy cycles.

SIR-C/X-SAR is the next step in a series of spaceborne imaging radars, beginning with Seasat in 1978 and continuing with SIR-A (1981), Germany's Microwave Remote Sensing Experiment (1983), and SIR-B (1984). It is the potential precursor for an Earth Observing System (EOS) SAR mission.

A total of about 50 hours of data, corresponding to roughly 50 million square kilometers of ground coverage, was collected during each mission. The ground swath width varies from 15 to 90 kilometers depending on the imaging mode and incidence angles of the radar beams.

Mission Objectives

Instrument Description

The SIR-C instrument was built by the Jet Propulsion Laboratory (JPL) and the Ball Communication System Division for NASA and is a two-frequency radar including L-band (23 cm wavelength) and C-band (6 cm wavelength) with four polarizations (HH, HV, VH, VV). The L- and C-bands use distributed phased-array antennas with electronic beam steering radars.

The X-SAR instrument was built by the Dornier and Alenia Spazio companies for DARA and ASI and is a single-frequency radar with X-band (3 cm wavelength) and vertical polarization (VV). X-SAR uses a passive slotted waveguide antenna and a tilt mechanism to point the radar beam in the same location as SIR-C's beam.

The science data are recorded aboard the space shuttle by the Payload High Rate Recorder. The data is played back from the High Density Digital Cassettes and processed into images by the Ground Data Processing System.

Background on Data Products

Two types of image products were produced by the ground data processing systems: the Survey product and the Precision (Standard) product. There were three ground data processing systems for SIR-C/X-SAR. JPL was responsible for Survey and Precision processing of the SIR-C data, while ASI was responsible for Survey processing of the X-SAR data. Precision processing of the X-SAR data was shared between the ASI and the DLR. From Fall 1996 to October 2002, the EDC DAAC assumed Precision product processing responsibilities. On October 2000 this responsibility was transitioned to the USGS at the Center for Earth Resources Observation and Science (EROS). Precision product processing was discontinued June 2005, after repeated system failures.

The survey product is a strip image of the entire data take (swath) processed to 50 m pixel spacing with approximately 100 m resolution for a single radar channel. The Precision product is a frame image of a subset of the data take. Only a small percentage of the acquired data were processed into Precision products, whereas all of the science data were processed into Survey products. The Survey product is intended as a "quick look" browsing tool for viewing the areas imaged by SIR-C/X-SAR and is not designed to be used for quantitative scientific analysis.

FTP distribution of Survey data products are available at:
and previously processed Precision products are available from EarthExplorer at:

More information is available in the following documents:

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Page Last Modified: June 23, 2008