Satellite Observations of the Elephant Butte Reservoir in New Mexico
Schmugge, T.; Bleiweiss, M.; Stein, W.
New Mexico State University

For many reservoirs there are considerable fluctuations in levels as water is drawn down for irrigation purposes. We present satellite observations of changes in the surface water area as evidence of this drawdown. Since the launch of NASA's Terra satellite in December 1999 the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer has made more than 30 observations of the Elephant Butte Reservoir located on the Rio Grande river in central New Mexico including night-time observations. The first observations were in June 2000 and continue to the present. This period includes low water levels resulting from the the recent drought conditions and the earlier full high water conditions in 2000, resulting in a 25m change in water level. This change indicated a reduction of the water storage by more than half. The area of the reservoir was estimated for each of these scenes and compared the with known water levels. Both visible reflectance and the thermal infrared data were used. These spectral regions provide good contrasts between water and surrounding land which makes the area estimation straightforward. A large range in surface water area was observed from 30,000 km*2 to more than 75,000 km*2. An approximately linear relation between area and water level was found. In addition to the area measurements there were surface temperature observations from both ASTER and MODIS (almost daily) . We also plan to explore the use of satellite altimetry for water level determinations.almost daily