Abstract
Multi-angular observation of land surface thermal radiation is considered to be a promising method of performing the angular normalization of land surface temperature (LST) retrieved from remote sensing data. This paper focuses on an investigation of the minimum requirements of viewing angles to perform such normalizations on LST. The normally kernel-driven bi-directional reflectance distribution function (BRDF) is first extended to the thermal infrared (TIR) domain as TIR-BRDF model, and its uncertainty is shown to be less than 0.3 K when used to fit the hemispheric directional thermal radiation. A local optimum three-angle combination is found and verified using the TIR-BRDF model based on two patterns: the single-point pattern and the linear-array pattern. The TIR-BRDF is applied to an airborne multi-angular dataset to retrieve LST at nadir (Te-nadir) from different viewing directions, and the results show that this model can obtain reliable Te-nadir from 3 to 4 directional observations with large angle intervals, thus corresponding to large temperature angular variations. The Te-nadir is generally larger than temperature of the slant direction, with a difference of approximately 0.5~2.0 K for vegetated pixels and up to several Kelvins for non-vegetated pixels. The findings of this paper will facilitate the future development of multi-angular thermal infrared sensors.
Highlights
Land surface temperature (LST) is required in many applications, including agrometeorology, climate and environmental studies [1,2]
According to the viewing azimuth angle (VAA) of each pixel of the three arrays shown in Figure 5b and the results shown in Figure 9, a cautious conclusion can be drawn that the larger the difference between the solar azimuth and the azimuth angles of array Forward 50°is, the better the result of the thermal infrared (TIR)-bi-directional reflectance distribution function (BRDF) model will be
This paper attempted to evaluate the minimum requirements of viewing angles to enable the angular normalization of land surface temperature by extending the kernel-driven BRDF model to the thermal infrared domain as TIR-BRDF model
Summary
Land surface temperature (LST) is required in many applications, including agrometeorology, climate and environmental studies [1,2]. Only ATSR (Advanced Along Track Scanning Radiometer) series satellites [31,32] have provided multi-angular observations of thermal infrared (TIR) data because of the difficulty and the complexity of manufacturing highly controlled multi-angular sensors and because no studies that discuss requirements in terms of the number of direction specifications of angular observations have been published. To address this situation, we investigate the minimum requirements of viewing observations and directions for achieving angular normalization of LSTs using multi-angular TIR data to provide technique support for the future design of such sensors. The full names and the corresponding abbreviations of some terms are listed in the Table A1 of Appendix
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