Submitted to: American Geophysical Union
Publication Type: Abstract only
Publication Acceptance Date: 10/15/2003
Publication Date: 12/8/2003
Citation: Hsu, A.Y., Jackson, T.J., O'Neil, P.E. 2003. An assessment of the use of AMSR e 10 ghz data for soil moisture estimation in SMEX02 [abstract]. EOS Transactions. 84(46):6813. Interpretive Summary:
Technical Abstract: The launch of the Advanced Microwave Scanning Radiometer (AMSR-E) on board the NASA EOS Aqua Satellite has drawn much interest from the scientific community that has been waiting for a low frequency spaceborne microwave radiometer (< 10 GHz) capable of measuring soil moisture. The AMSR-E instrument was developed by the National Space Development Agency of Japan (NASDA) and makes dual-polarized microwave measurements at six frequencies: 6.9, 10.7, 18.7, 23.8, 36.5, and 89 GHz. Early examinations of AMSR-E measurements have shown evidence of extensive Radio-Frequency Interference (RFI) in the 6.9 GHz channels, especially over the continental U.S. Due to the contamination of 6.9 GHz data by RFI, it may be necessary to use the next lowest frequency, 10.7 GHz, for soil moisture retrieval. This frequency has been available on the TRMM Microwave Imager for several years; however, the TRMM sensor only provides data between 38 N to 38 S in latitude whereas AMSR-E provides global coverage. We examined the impact of alternative frequencies on soil moisture retrieval using data from the Soil Moisture Experiments in 2002 (SMEX02). SMEX02 took place in Walnut Creek Watershed and surrounding region of Iowa from June 24 to July 12. The experiment focused on microwave remote sensing of soil moisture in an agricultural setting. Landcover in the Walnut Creek Watershed consists of a patchwork of corn and soybean fields, with some isolated forested zones. This presents a challenge to soil moisture retrieval using AMSR-E 10 GHz data. Extensive vegetation sampling was conducted during SMEX02 to provide information to estimate vegetation parameters required by retrieval algorithm. The maps of AMSR-E 10 GHz data over SMEX02 area from July 2 to 13 show the decrease of brightness temperature (TB) due to precipitation, although the range is not as profound as expected at L band. The Normalized Difference Polarization Index (NDPI), defined as (TBv-TBh)/(TBv+TBh), computed for various frequencies can be considered as indicators of surface vegetation conditions and soil moisture. The plots of NDPI at 10.7, 18.7 and 36.5 GHz over the SMEX02 area show distinct differences between 36.5 and 10.7 and 18.7 GHz data. This study aims to explore the use NDPI at different frequencies in estimating soil moisture from a densely vegetated area at the AMSR-E 10 GHz footprint scale.