APPLICATION OF REMOTE SENSING FOR HYDROLOGICAL STUDIES IN THE NEBRASKA SANDHILLS

Remote sensing methods were applied for delineation of the groundwater flow system in the Western Sandhills, Nebraska. We hypothesize that the spatial and temporal temperature anomalies can be used as indicators of ground water discharge to the lakes and their relationships with the regional groundwater flow. The Landsat images of Crescent Lake National Wildlife Refuge (Crescent, Blue, Island, and Hackberry lakes) were acquired for different seasons of the year. During warm season, cooler zones indicate groundwater inflow (warm season patterns), while during cool season the warmer zones indicate the groundwater inflow (cold season patterns).

Distribution of uncorrected surface temperatures was evaluated using processed Landsat thermal infrared data, acquired in summer and early fall. Each lake exhibits one or several zones with warm season patterns. These findings are consistent with data from Thermal Infrared Multispectral Scanner (Rundquist et al., 1985). They are also consistent with the results of reconnaissance of the Crescent Lake in January 2002, when the first ice melting was found in the same zones. We attribute this phenomenon to warmer lake temperatures near the groundwater inflow zones. In this case, temperature distribution was less affected by wind or solar radiation.

To corroborate the remote sensing-based methodology with ground-based data, spatially and temporally distributed measurements of the lakes temperatures were conducted in the summer 2002 on the dates of the Landsat-7 ETM+ sensor data acquisition. Spatial distributions of lake temperatures at different depths in three lakes were obtained and compared with the surface temperatures. In most cases, lake temperatures at some depths are correlated to the surface temperatures obtained from Landsat data. As a result, the hypothetical hydrological model of small portion of Sandhills was constructed. This model correlates well with hydrostratigraphic data inferred from previous studies in the area.