User:Ke4roh/SIR-C/X-SAR

SIR-C/X-SAR, (Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar), was a radar for earth observation that pioneered multiband, polarimetric earth observation by synthetic aperture radar from space. The payload flew in the northern hemisphere's spring and fall of 1994 on, STS-59 and STS-68, collecting information to be used in the fields of ecology, hydrology, geography, oceanography, topography, archaeology, and wildlife preservation.

Scientists pre-selected certain targets for observation and analysis based on their suitability for one of the fields of research to be conducted, and/or for calibration of the instruments. The radars were then used to carry out several experimental SAR techniques including interferometry through multiple passes and radar beam elevation steering through ScanSAR.

The same hardware flew once more on Endeavour on STS-99, named Shuttle Radar Topography Mission (SRTM), which included the addition of a 60 m mast and outboard C-Band and X-band antennas to allow for single-pass interferometry.

Predecessors
Seasat was the first space-based SAR, operating in 1978. Seasat included an L band (23.5 cm) SAR, horizontally polarized for send and receive, always looking at 45° off nadir. The satellite included other instruments: an altimeter, microwave scatterometer, and microwave, visible, and infrared radiometers.

The Shuttle carried spare SAR equipment from Seasat for SIR-A on STS-2, assessing the Shuttle as a platform for earth-observing radar and establishing an understanding of radar signatures for geologic features. The radar was again L band, with a fixed angle of 47° off nadir. SIR-A produced optical data only.

The same hardware was rebuilt to allow antenna tilt to change the incidence angle between 15° and 60°, and it flew again as SIR-B on STS-41-G.

Instruments
SIR-C had an active phased array antenna that could steer the beam electronically and illuminate multiple swaths, collecting data polarized both horizontally and vertically on C and L bands. SIR-C was developed by NASA's Jet Propulsion Laboratory and Ball Aerospace Corporation's Communications Systems Division.

X-SAR used a slotted waveguide antenna to collect vertically polarized signals using X-band radar. X-SAR was developed by Spazio for Deutschen Zentrum für Luftund Raumfahrt (DLR), and Agenzia Spaziale Italiana (ASI).

These instruments were used in a number of experimental modes which demonstrated the technology and were subsequently re-used on other spacecraft. Flight hardware processed images taken by ScanSAR, also known as burst-mode SAR, into images covering swaths wider than 200km, used later by Radarsat 1. Polarization diversity on advanced SAR (ASAR) flew on Envisat, and Advanced Land Observation Satellite followed with a similar PALSAR technique. Johns Hopkins University Applied Physics Laboratory provided an onboard processor for generating ocean wave spectra. Along-track and cross-track interferometry provided detailed elevation data for surveyed areas, which later took the most complete high-resolution survey of the globe's topography on the Shuttle Radar Topography Mission.