North-Central Gulf of Mexico Imagery
The images in this section were obtained from the CD-ROM publication "Satellite Imagery of the North-Central Gulf of Mexico" (Stumpf, 1998). Sea surface temperature, reflectance, and false-color infrared images were selected from March, April and May of 1996 and 1997 to show the area during the 1997 Bonnet Carré Spillway opening as well as during another year for comparison. (The CD-ROM includes more comprehensive data from June 1993 to May 1997.) The regional view displayed here is presented in TIF format files having a size of 512 pixels by 256 lines. The nominal pixel size in the images is approximately 1 km x 1 km.
The imagery set contained here is presented in a Mercator projection with a scale (pixel width) of 1.0845 km at the central latitude of 29° 45' N. This corresponds to a map scale of 1.25 km per pixel at the equator (the Mercator projection has a scale which varies with latitude). The images are 512 pixels across and 256 lines high and extend from from 28° 30' N to 30° 59.5' N and from 86° 06' W to 91° 51 W.
The remapping process used the nearest-neighbor technique. In this technique, the latitude and longitude is determined for each point in the raw data. The values (SST, reflectance, etc.) for this point are then assigned to the nearest pixel in the mapped image that has the same latitude and longitude. Not all locations or pixels in the mapped image received data. Pixels in the mapped image that did not receive values from the raw data were filled using an average of the values in the surrounding 3x3 block of pixels. About 10% of the mapped pixels were not assigned values from the raw data and were filled using the local average.
The clock on board the spacecraft has a drift that leads to errors of 3-8 km in the calculated positions of the pixels. To correct for these errors, the output images were manually shifted to conform to a shoreline to within 1 pixel. This shift concentrated on Mobile Bay, which is at the center of the mapped image. Slight nonlinearities in the georeferencing may still lead to errors of >1 pixel (1 km) in the pixel position near the left and right edges of the mapped image.
U.S. Department of the Interior, U.S. Geological Survey
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Last modified: 22:32:04 Thu 10 Jan 2013
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