March 20, 1998
AirMISR Flight of 20 March 1998, JPL, Pasadena, CA
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.