A general description of the Airborne Multi-angle Imaging Spectro-Radiometer (AirMISR) is given on the AirMISR page.
The images included below are from AirMISR operational flight No. 4, over
Pasadena, California, and includes the location of NASA's Jet Propulsion Laboratory, where AirMISR was
built and is maintained. The primary target for the day was the snow-covered
area of Mammoth Mountain, at the southern end of the Sierra Nevadas in southern
California. However, that area was cloud covered, so the alternative Pasadena
target was used. Whenever possible, one or two backup flight plans are prepared
in case the primary flight plan is not practicable, usually for weather-related
reasons.
Pasadena is situated 20 kilometers north of Los Angeles, at the western end
of the San Gabriel Valley, at an elevation of approximately 300 meters.
Immediately to the north are the San Gabriel Mountains, which extend up to
around 1,600 meters elevation within a short distance from Pasadena. The frontal
range of the San Gabriels is visible is some of these AirMISR images, especially
the second
flight run. Features of the Pasadena area are clearly seen in many of the
images, including a maze of city streets, freeways, individual buildings,
and even some mountain roads. The nadir
view for flight run 1 shows the triangle formed by the 134 Freeway running
approximately east-west at the bottom, the 210 Freeway running towards the
northwest, and the 2 Freeway running approximately north-south at the left hand
side. In the middle of the triangle are the San Rafael Hills, forming a natural
boundary between the Pasadena and Glendale communities. To the right of these
hills, still within the triangle, is the circular donut appearance of the Rose
Bowl, a large stadium in Pasadena with a seating capacity of over 100,000
people, and the adjacent Brookside Golf Course. Just to the north-east of the
freeway triangle is the myriad of buildings constituting the Jet Propulsion
Laboratory. The downtown area of Pasadena is immediately to the south-east of
the bottom right-hand corner of the triangle.
Many of these images contain clouds. Clouds are a vital item of interest in
the overall MISR experiment. You can see from the arrays of small thumbnail
images presented below that within one flight run the clouds are apparent in
some images but almost completely absent in others. In certain instances, the
same clouds are in different positions in different images. Although the clouds
themselves may have moved during the 11-12 minutes of a flight run, much of the
cloud difference between images of the same run is a result of the varying
angles of view of the AirMISR camera. In particular, if the camera is pointing
towards the north, the clouds will appear to be shifted northward, and vice
versa for southerly inclined views. The inclined view also means we can
see under the edge of a cloud to the ground surface beneath the cloud, and yet
that ground surface is totally obscured in the vertically-downward nadir view.
By measuring the degree of these so-called "stereo" effects, and
taking into account the aircraft's motion, it is possible to make
deductions about both the cloud motion and the cloud height. The ability to make
these measurements on a global basis is one of the goals for the spaceborne MISR
instrument.
Also of interest is the general texture and structure of the clouds, these
being features that have a direct bearing on the amount of sunlight reflected by
the clouds, and hence the degree to which the sun's radiation is warming the
Earth. A more in-depth discussion of the ways in which MISR will be used to
study clouds is given on the MISR science goals
page.
The Pasadena flight occurred at around 10 a.m. on 20 March 1998. Each of the
images covers an area approximately 10 km on a side, and was acquired from the
ER-2 aircraft flying at 20 kilometers altitude. During this flight, three runs
were made over the target area. the first was from north to south, the
second from south to north, and the third from north to south.
All of the images below are of the AirMISR red "band" (one of AirMISR's four
colour channels,) which has a wavelength of 670 nanometers. The images have been
flipped and rotated into the correct geographic orientation with north roughly
toward the top. Included are both "raw" images and radiometrically calibrated
images (radiances.) Subsequent processing will georectify the images,
eliminating the effects of rapid aircraft pitch, roll, and yaw changes. From the
aircraft altitude of 20,000 meters, the nadir (An) views have a resolution of 7
meters. The D-aft view is ultimately intended to be at 70.5 degrees; however, at
the time of this flight the instrument was capable of reaching only 67.5 degrees
in this direction because of a temporary mechanical issue.
