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United States Department of Agriculture

Agricultural Research Service


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Title: L-Band Microwave Observations over Land Surface Using a Two-Dimensional Synthetic Aperture Radiometer)

item Ryu, Dongryeol
item Jackson, Thomas
item Bindlish, Rajat
item Le vine, David

Submitted to: Geophysical Research Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/1/2007
Publication Date: 10/1/2007
Publication URL:
Citation: Ryu, D., Jackson, T., Bindlish, R., LeVine, D. 2007. L-Band microwave observations over land surface using a two-dimensional synthetic aperture radiometer. Geophysical Research Letters. 34, L14401,

Interpretive Summary: Although microwave radiometry at L-band (~1.4 GHz) has been known as an optimal solution for remote-sensing of soil moisture, the constraint on large antennas size required for the low-frequency radiometry has limited the development of L-band satellite instrument for global-scale observation. This limitation can be overcome by using an interferometric technology, called aperture synthesis. The objective of this experiment was to demonstrate the soil moisture mapping capability of the first aircraft L-band radiometer that employed two-dimensional aperture synthesis. During the Soil Moisture Experiment in 2003 (SMEX03), the two-dimensional synthetic aperture radiometer (2D-STAR) was flown onboard an aircraft over a regional-scale site located in Alabama, which had various land surface conditions including crop fields, pasture, and forest. There was fairly good radiometric sensitivity of instrument to the soil moisture in both pasture and forest areas. The 2D-STAR’s sensitivity to the soil moisture under dense vegetation canopy was remarkably superior to a conventional high-frequency radiometer that was used in the same experiment. The results of this study are very important to the future of spaceborne remote sensing and provide justification for the further development of this technology. The improved remote sensing capabilities of L-band interferometric radiometry will be of benefit to hydrologic applications in agriculture and climate.

Technical Abstract: Antenna size is major factor that has limited realization of the potential capabilities of L-band (1.4 GHz) microwave radiometry to estimate surface soil moisture from space. However, emerging interferometric technology, called aperture synthesis, has been developed to address this limitation. The Soil Moisture and Ocean Salinity (SMOS) mission will apply the technique to monitor these parameters at a global-scale in the near future. The first airborne experiment using an aircraft prototype called the Two-Dimensional Synthetic Aperture Radiometer (2D-STAR) was performed in the Soil Moisture Experiment in 2003 (SMEX03). To gain insight, the L-band brightness temperature data acquired by 2D-STAR in Alabama was compared with C-band data collected simultaneously by another aircraft instrument called the Polarimetric Scanning Radiometer (PSR), and also compared with surface soil moisture measurements from in-situ observations sites. Results show that there was fairly good radiometric sensitivity of the synthetic aperture radiometer to the soil moisture both in pasture and also in forest areas. The overall performance of the L-band synthetic aperture radiometer in the presence of vegetation appears to be better than the C-band real aperture radiometer.

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