Airborne Multi-angle Imaging SpectroRadiometer (AirMISR)
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NOTE: AirMISR was withdrawn from active service in September 2004 following a successful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. This introductory web page and the
Guide for Investigators
remain in place because AirMISR data
continues to be available, and because the instrument could potentially be used again.
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 Dryden Flight Research Center,
at Edwards, 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)
Technical description
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.
View recent AirMISR Flight Imagery
View an archive of example AirMISR Flight Imagery
View information on AirMISR deployments
See Photographs of the AirMISR Instrument
Read the Guide for Investigators
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