Relationships between evaprorative fraction and remotely sensed vegetation index and microwave brightness temperature for semiarid rangelands

Journal Article · Wed Dec 01 00:00:00 EST 1993 · Journal of Applied Meteorology

DOI:https://doi.org/10.1175/1520-0450(1993)032<1781:RBEFAR>2.0.CO;2· OSTI ID:45901

Kustas, W P; Schimugge, T J; Humes, K S; Jackson, T J; Parry, R; Weltz, M A; Moran, M S ^[1]

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1. USDA-ARS, Beltsville, MD (United States)

Measurements of the microwave brightness temperature (TB) with the Pushbroom Microwave Radiometer (PBMR) over the Walnut Gulch Experiment Watershed were made on selected days during the MONSOON 90 field campaign. The PBMR is an L-band instrument (21-cm wavelength) that can provide estimates of near-surface soil moisture over a variety of surfaces. Aircraft observations in the visible and near-infrared wavelengths collected on selected days also were used to compute a vegetation index. Continuous micrometeorological measurements and daily soil moisture samples were obtained at eight locations during experimental period. Two sites were instrumented with time domain reflectometry probes to monitor the soil moisture profile. The fraction of available energy used for evapotranspiration was computed by taking the ratio of latent heat flux (LE) to the sum of net radiation (Rn) and soil heat flux (G). This ratio is commonly called the evaporative fraction (EF) and normally varies between 0 and 1 under daytime convective conditions with minimal advection. A wide range of environmental conditions existed during the field campaign, resulting in average EF values for the study area varying from 0.4 to 0.8 and values of TB ranging from 220 to 280 K. Comparison between measured TB and EF for the eight locations showed an inverse relationship. Other days were included in the analysis by estimating TB with the soil moisture data. Because transpiration from the vegetation is more strongly coupled to root zone soil moisture, significant scatter in this relationship existed at high values of TB or dry near-surface soil moisture conditions.

• Research Organization: National Aeronautics and Space Administration (NASA), Washington, DC (United States)
• OSTI ID: 45901
• Journal Information: Journal of Applied Meteorology, Vol. 32, Issue 12; Other Information: PBD: Dec 1993
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ARID LANDS
REMOTE SENSING
GROUND COVER
EARTH PLANET
ENERGY BUDGETS
HEAT FLUX
ARIZONA
WATERSHEDS