AirMISR -- the Airborne Multi-angle Imaging SpectroRadiometer -- is a an airborne instrument for obtaining multi-angle imagery similar to that of the satellite-borne MISR instrument, which is designed to provide new types of information for scientists studying Earth's climate. AirMISR flies on the NASA-owned ER-2 aircraft. It was built for NASA by the Jet Propulsion Laboratory in Pasadena, California.
NOTE: AirMISR was withdrawn from active service in September 2004 following a successful operational life of approximately seven years supporting a variety of MISR and other scientific campaigns in North America and southern Africa. Parts from AirMISR were used to construct a new instrument named the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI), which flies as part of JPL’s Airborne Science Program. This introductory web page and the Guide for Investigators remain in place because AirMISR data continue to be available.
An introduction to AirMISR
There are few existing sources of multiangle imagery of the sort MISR acquires, other than the MISR instrument itself. Therefore, an important tool for scientists needing an independent confirmation of MISR's observations is the aircraft version of MISR, called AirMISR, which flies on one of the NASA-owned ER-2 high-altitude research aircraft based at NASA Armstrong Flight Research Center, at Palmdale, California. This aircraft flies at 20,000 meters (65,000 feet,) which is above more than 90 percent of the Earth's atmosphere. There is no room for anyone but the pilot, who must wear a pressure suit because of the altitude. At 20,000 meters, Earth looks very much like it does from space. AirMISR must operate by itself, just like a spacecraft sensor.
The first flights of AirMISR occurred during 1997. AirMISR was a valuable source of multiangle data for scientists prior to the launch of MISR, which did not occur until December of 1999. Every year, there are campaigns where AirMISR flies under the path of its satellite sister, taking measurements that allow comparisons between the two instruments. Scientists can then determine how the sensitivities of the MISR cameras change with time, which ensures that MISR data are correctly interpreted by the many scientists and organizations who rely on MISR.
AirMISR is also deployed during large field campaigns where many scientists are collecting simultaneous ground measurements. In these instances, it is used as one of many instruments to study a given site intensely. This complements the MISR data, for which there are fewer coincident observations from other sensors.
Data from AirMISR can also be used in its own right for scientific research. It has the advantage that its data is processed to produce data products having a spatial resolution on the ground that is ten times better than the spaceborne MISR.
One particular problem space instruments have is that strong UV light from the sun can turn the lenses brown. This effect is minimized with MISR because good materials were used, and because each lens surface was cleaned carefully prior to launch. AirMISR will help scientists understand how successfully MISR copes with this problem, and how to make allowances for it. For further information about the uses of AirMISR, see the pages about calibration and validation. The photo above shows testing of the AirMISR instrument, installed in the nose of the ER-2 aircraft. (Click on the picture to see an enlarged photograph)
AirMISR was fabricated partly from parts left over from the construction of MISR, including parts from the so-called brassboard and engineering models built to prove the design before the MISR instrument was finally constructed. Unlike the spaceborne MISR instrument, which has nine cameras oriented at various angles, AirMISR utilizes a single camera in a pivoting gimbal mount. A data run by the ER-2 aircraft is divided into nine segments, each with the camera slewed to a different MISR look-angle. The gimbal rotates aft between successive segments, such that each segment acquires data over the same area on the ground as the previous segment. This process is repeated until all nine look-angles of the target area are collected. The swath width, which varies from 11 km in the nadir to 32 km at the most oblique angle, is governed by the camera's instantaneous field-of-view of 7 meters cross-track x 6 meters along-track in the nadir view and 21 meters x 55 meters at the most oblique angle. The along-track image length at each angle is dictated by the timing required to obtain overlap imagery at all angles, and varies from about 9 km in the nadir to 26 km at the most oblique angle. Thus the nadir image, which is the smallest, dictates the area of overlap obtained from all nine look angles. A complete flight run takes approximately 12 minutes.
The use of a single camera to provide coverage at all nine angles is possible because AirMISR is not attempting to obtain continuous, global coverage, as is the case with the spaceborne MISR. This approach ensures identical calibration at all angles, a useful feature in utilizing the instrument as part of the MISR calibration.