Synthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR) MASINT
A Synthetic aperture radar (SAR) system, exploits the fast movement of an aircraft or satellite, simulating a large antenna by combining samples over time. This simulation is called the synthetic aperture.
Coupled with other MASINT and IMINT sensors, SAR can provide a high resolution, day and night collection capability. Recorded over time, it can be excellent for tracking changes. In addition, when operated at appropriate frequencies, it has ground- and water-penetrating capability, and is good for picking objects out of deliberate or natural clutter.
SAR is not, however, a trivial computational task. As the real antenna moves past the target, the range between target and antenna changes, which must be considered in synthesizing the aperture. In discussing SAR principles, Sandia National Laboratories also notes that, "for fine resolution systems, the range and azimuth processing is coupled (dependent on each other) which also greatly increases the computational processing".
In spite of the difficulties, SAR has evolved to a size that can fit aboard a UAV. Flying on the MQ-1 Predator, the Northrop Grumman AN/ZPQ-1 Tactical Endurance Synthetic Aperture Radar (Tesar) started operations, in March 1996, over Bosnia. The AN/ZPQ-1 uses a radar signal in the 10 – 20 GHz J-band, and can work in strip map, spot map, and MTI modes. These modes are applicable to a wide range of MASINT sensors.
Strip map imaging observes terrain parallel to the flight path or along a specified ground path. Resolution depends on range and swath width, and can vary from 0.3 to 1.0 metres.
Compare the two. The radar is not affected by night or weather.
Spot map mode covers 800 x 800 metres or 2400 x 2400 metres. In MTI mode, moving targets are overlaid on a digital map.
As well as large SAR aircraft such as the E-8 Joint Surveillance Target Attack Radar System (Joint STARS), whose AN/APY-3 radar has multiple modes including ground moving target indication, the US has highly classified radar satellites. Quill launched in 1964, was the first radar satellite, essentially a prototype. A system originally called Lacrosse (or Lacros), Indigo, and finally Onyx appears to be the only US radar satellite system, using pushbroom scans and "spotlighting" SAR.
Given that the E-8 is a large aircraft that cannot defend itself, there are US attempts to move the E-8 capability into space, under a variety of names, most recently a simple "Space Radar". In an era of budget demands, however, this extremely costly new generation has not been launched.
ISAR can produce actual images, but the discipline is generally called MASINT rather than IMINT.A much more modest ISAR capability is on the Navy's SH-60 multimission helicopter, carried on destroyers, cruisers, and aircraft carriers. If budgets permit, the proposed E-8 aircraft, the replacement for the P-3 maritime surveillance aircraft, will carry ISAR.
P-3 aircraft carry the AN/APS-137B(V)5 radar, which has SAR and ISAR capability. This is part of the general upgrading of the P-3 to make it a capable land surveillance platform.
The German Armed Forces' (Bundeswehr) military SAR-Lupe reconnaissance satellite system has been fully operational since July 22, 2008.
Read more about this topic: Radar MASINT
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