Lat/Long Adjustment Tool

Geographic coordinates for each ASTER scene are stored in various places in the HDF and *.met files. Latitude/longitude values are assigned to certain image pixels, based on knowledge of spacecraft attitude and pointing, instrument pointing, and line of sight vectors for each detector. Over the last 5 years, we have discovered several small errors that can affect the accuracy of these coordinates:

1. An error in the value of the Earth rotation rate caused a geolocation error in the daytime scenes of up to 300 m near the poles, but less than 100 m below 70 degrees latitude; for nighttime observations, the longitude error is largest at the equator, and decreases to 100 m at the poles.
2. Not compensating for nutation of the earth’s rotation axis caused an acquisition-date-dependent longitude error of up to 200 m.
3. Altitude compensation: ASTER coordinates are  projected to the WGS-84 ellipsoid, rather than the real earth’s surface. In the most extreme case for areas of high relief (Tibet, for example), and maximum off-nadir viewing, the relief displacement in longitude can be 400 m. Compensation requires a digital elevation model.

Corrections for errors 1 and 2 were incorporated into the Level 1 processing software at the time they were identified. For all  Level 1 processing, no compensation is made for elevation displacement.

For older data, we have made available a web-based tool that will prompt you to upload your ASTER HDF files to our ftp server. We will apply all of the appropriate coordinate adjustments to your data, dependent on date of acquisition and processing. You will also have the option to convert your scenes to GeoTiff format. Then you will download your adjusted GeoTiff and/or HDF scenes.

 USE ONLY ON LEVEL 1B DATA, WITH A .HDF EXTENSION

Lat/Long Adjustment Tool