Estimation of soil and vegetation temperatures with multiangular thermal infrared observations: IMGRASS, HEIFE, and SGP 1997 experiments

The potential of directional observations in the thermal infrared region fo r land surface studies is a largely uncharted area of research. The availab ility of the dual-view Along Track Scanning Radiometer (ATSR) observations led to explore new opportunities in this direction, In the context of studi es on heat transfer at heterogeneous land surfaces, multiangular thermal in frared (TIR) observations offer the opportunity of overcoming fundamental d ifficulties in modeling, sparse canopies. Three case studies were performed on the estimation of the component temperatures of foliage and soil, The f irst one included the use of multi-temporal field measurements at view angl es of 0 degrees, 23 degrees and 52 degrees, The second and third one were d one with directional ATSR observations at view angles of 0 degrees and 53 d egrees only. The first one was a contribution to the Inner-Mongolia Grassla nd Atmosphere Surface Study (IMGRASS) experiment in China, the second to th e Hei He International Field Experiment (HEIFE) in China and the third one to the Southern Great Plains 1997 (SGP 1997) experiment in Oklahoma, United States, The IMGRASS experiment provided useful insights on the applicabili ty of a simple linear mixture model to the analysis of observed radiance, T he HEIFE case study was focused on the large oasis of Zhang-Ye and led to u seful estimates of soil and vegetation temperatures. The SGP 1997 contribut ed a better understanding of the impact of spatial heterogeneity on the acc uracy of retrieved foliage and soil temperatures, Limitations in the approa ch due to varying radiative and boundary layer forcing and to the differenc e in spatial resolution between the forward and the nadir view are evaluate d through a combination of modeling studies and analysis of field data.