Remote Sensing for Mapping Near-Surface Playa Moisture

Affiliation(s) PI/CoPI Funded by
DEES

McDonald, Eric
Caldwell, Todd
Sabol, Don

Army Research Office

Keywords: playa, Soda Lake, ASTER, MASTER, soil moisture, trafficability, soil temperature

Project Description

The relationship of near-surface moisture in desert playas to surface temperature is being studied for the purpose of using remote sensing to map subsurface moisture. This study is focused on two playas in the Mojave Desert of California: 1) a seasonally moist playa (Soda Lake Playa), and 2) a dry playa (Superior Playa). Detection and monitoring of near-surface moisture is important for understanding processes of desert landform evolution. Also, it is an important factor in determining trafficability and dust generation from vehicle operations.

Soda Lake Playa lies near the modern terminus of the Mojave River and can contain standing water in wet years. During drier periods (as during this study), the surface is dry with moist lake silts below. Hot dry weather drives capillary movement of water upward near the surface where it evaporates. In areas where this action is greatest (the western half of the playa) evaporite deposits (e.g. sodium carbonate, sodium bicarbonate) are formed. This is in sharp contrast to dry playas (Superior Playa) where the lake sediments are relatively dry to depths of 0.5 meters or more.

Field sites were established on each playa to sample the maximum variability of near-surface soil moisture and surface composition. At each site, thermocouples were imbedded in the soil at depths and data loggers were used to record temperatures at selected sites during satellite and/or aircraft overflights using airborne ASTER simulator data, and MASTER.

Radiant surface temperatures derived from the satellite and airborne image data were compared to field measured radiant temperatures and bulk surface temperatures (from thermocouples). These temperature profiles were then compared to soil moisture profiles. Day/night image data were used to produce an "apparent thermal inertia" image to identify areas of greatest sub-surface moisture. To confirm theses results, field-measured day/night temperature images were made of an area of the Soda Playa containing both moist and dry zones, using a hand-held FLIR camera.

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Trafficability due to seasonal wetness is a common issue to the National Park Service, responsible for maintaining the Old Mojave Road across Soda Lake Playa. Characterization of a wet playa (Soda Lake) along the Old Mojave Road. The capillary rise of evaporating groundwater forms a thick salt crust which acts to inhibit 'drying' of the surface and reduces wheel traction.

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