Monday, November 13, 2006 - 9:15 AM

Predicting Evaporation from Soil Surfaces using Remotely Measured Spectral Data.

Dong Wang1, Jindong Wu2, and Edward Dorsey2. (1) University of Minnesota, USDA-ARS, SJVASC,, 9611 S. Riverbend Ave.,, Parlier,, MN 93648, (2) Univ of Minnesota, 1991 Upper Buford Cir., St. Paul, MN 55108

Evaporation from soil surfaces is a major component of surface water and energy budgets. The potential ability to predict soil evaporation with remote sensing measurements has great implications for understanding land surface processes. The objective of this study was to explore algorithms of predicting soil evaporation based on remotely measured spectral reflectance and temperature data.  A 16-band spectral radiometer was used for the reflectance measurements.  An infrared thermometer was used for the temperature measurement.  To make simultaneous radiometric and evaporation measurements, a large steel apparatus was fabricated which contained a fame to support the radiometer over a soil tray placed directly on top of an electronic scale. A large steel beam was used to counter-balance the weight of dry soil and soil tray, so the scale measured only change in water content in the tray. During each measurement, the tray was filled with one type of soil, saturated with water, then started the overtop reflectance and weight-change measurements while evaporation was occurring. The experiments were carried out in clear, calm, sunny days, and repeated for different soil types.  A band index was created to maximize changes of soil surface spectral properties associated with water content decrease during evaporation. A linear empirical relationship was developed for predicting evaporation using the most sensitive band indices and surface radiometric temperature measurements. The preliminary results served as a proof of concept.  More testing or validation is needed before using the technique in actual field applications with aircraft or satellite images.