Arid and semiarid rangelands comprise a significant portion of the earth's land surface. Yet little is known about the effects of temporal and spatial changes in surface soil moisture on the hydrologic cycle, energy balance, and the feedbacks to the atmosphere via thermal forcing over such environments. Understanding this interrelationship is crucial for evaluating the role of the hydrologic cycle in surface–atmosphere interactions.

This study focuses on the utility of remote sensing to provide measurements of surface soil moisture, surface albedo, vegetation biomass, and temperature at different spatial and temporal scales. Remote-sensing measurements may provide the only practical means of estimating some of the more important factors controlling land surface processes over large areas. Consequently, the use of remotely sensed information in biophysical and geophysical models greatly enhances their ability to compute fluxes at catchment and regional scales on a routine basis. However, model calculations for different climates and ecosystems need verification. This requires that the remotely sensed data and model computations be evaluated with ground-truth data collected at the same areal scales.

The present study (MONSOON 90) attempts to address this issue for semiarid rangelands. The experimental plan included remotely sensed data in the visible, near-infrared, thermal, and microwave wavelengths from ground and aircraft platforms and, when available, from satellites. Collected concurrently were ground measurements of soil moisture and temperature, energy and water fluxes, and profile data in the atmospheric boundary layer in a hydrologically instrumented semiarid rangeland watershed. Field experiments were conducted in 1990 during the dry and wet or “monsoon season” for the southwestern United States. A detailed description of the field campaigns, including measurements and some preliminary results are given.

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1USDA-ARS Hydrology Lab., Beltsville, Maryland

2USDA-ARS Aridland Watershed Management Research Unit, Tucson, Arizona

3USDA-ARS U.S. Water Conservation Lab., Phoenix, Arizona

4USGS-Water Resources Division, Denver, Colorado

5Utah State University Dept. of Soil Science and Biometeorology, Logan, Utah

6University of Arizona, School of Renewable Natural Resources, Tucson, Arizona

7USSR Academy of Sciences, Institute of Radioengineering and Electronics, Moscow, USSR

8USDA-ARS Remote Sensing Research Lab., Beltsville, Maryland

9USGS-Water Resources Division, Carson City, Nevada

10University of Maryland, Department of Meteorology, College Park, Maryland

11University of Arizona, Department of Soil and Water Science, Tucson, Arizona

12University of Arizona, Department of Hydrology and Water Resources, Tucson, Arizona

13LERTS, Toulouse, France

14CEMAGREF-ENGREF, Remote Sensing Lab., Montpellier, France

15University of Arizona, Department of Optical Sciences, Tucson, Arizona

16Los Alamos National Lab., Los Alamos, New Mexico

17Jet Propulsion Lab., Pasadena, California