A four-state field evaluation of the Boeing Landing Suitability Index (BLSI) for automatically mapping candidate aircraft operating sites in natural terrain from LANDSAT TM data

摘要

The Boeing Landing Suitability Index (BLSI) is a computer algorithm designed at Bowling Green State University for The Boeing Company for the purpose of mapping candidate aircraft operating sites of different "runway" lengths in natural terrain from LANDSAT TM data. Four LANDSAT TM frames (each 115 miles x 115 miles in area) from parts of California, New Mexico, South Dakota, and Louisiana (with annual rainfalls averaging approximately 3.5, 7, 17, and 53 in., respectively, though the Louisiana frame was collected during a drought year that had 28 in. of annual rainfall) were entered as inputs to the BLSI algorithm, which identified pixels in each of the frames that were sufficiently flat, treeless, and absent of surface water to land an aircraft on them, present weather conditions permitting, and perform off-loading, on-loading, and take-off operations. Adjustments were made to the algorithm for differences in annual rainfall. Although no attempt was made before these field trips to force BLSI to map surface firmness, the California Bearing Ratio (CBR) was measured in the field on-site and off-site with dynamic cone penetrometers by a contractor for the Air Force Research Lab (Tyndall AFB in Florida) for several of these candidate aircraft operating sites. We found that all of the sites selected by BLSI that were visited in the field were suitably flat for landing and had no surface water or trees on them (except for one small tree that was younger than the LANDSAT frame employed for that region). Fortunately, most of these candidate aircraft operating sites found by BLSI had firmer ground than their immediate surroundings, as measured from the dynamic cone penetrometers. Our field observations support the hypothesis that BLSI is primarily mapping very subtle, local topographic highs. Such a subtle topographic high, which may rise only few feet from the middle to the edge of a candidate aircraft operating site, usually has a hard pan beneath it, owing to its relatively better drainage, compared with its immediate surrounds. This may account for its greater firmness, compared to its surrounds. Because the slopes are so small and the feature is slightly convex upward, there are no gullies on candidate aircraft operating sites. This causes the subtle topographic highs to be very flat and without rocks, unlike higher-sloped regions, where water in gullies tend to wash rocks. This seems the most reasonable explanation for why a pixel size as gross as 28.5 m (LANDSAT TM bands 1-5 and 7) is adequate to map such features. BLSI displayed as a continuous-toned image has potential for mapping areas of highest trafficability for wheeled vehicles, with lower BLSI values (shown as purple or blue areas) having the greatest trafficability.