Enric Valor i Mico

Simulation and validation of land surface temperature algorithms for MODIS and AATSR data

A database of global, cloud-free, atmospheric radiosounding profiles was compiled with the aim of simulating radiometric measurements from satellite-borne sensors in the thermal infrared. The objective of the simulation was to use Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) and Envisat/Advanced Along Track Scanning Radiometer (AATSR) data to generate split-window (SW) and dual-angle (DA) algorithms for the retrieval of land surface temperature (LST). The database contains 382 radiosounding profiles acquired from land surfaces, with an almost uniform distribution of precipitable water between 0 and 5.5 cm. Radiative transfer calculations were performed with the MODTRAN 4 code for six different viewing angles between 0 and 65. The resulting radiance spectra were integrated with the response filter functions of MODIS bands 31 and 32 and AATSR channels at 11 and 12 μm. Using the simulation database, SW algorithms adapted for MODIS and AATSR data, and DA algorithms for AATSR data were developed. Both types of algorithms are quadratic in the brightness temperature difference, and depend explicitly on the land surface emissivity. These SW and DA algorithms were validated with actual ground measurements of LST collected concurrently with MODIS and AATSR observations in a large, flat and thermally homogeneous area of rice crops located close to the city of Valencia, Spain. The results were not bias and had a standard deviation of around ± 0.5 K for SW algorithms at the nadir of both sensors; the SW algorithm used in the forward view resulted in a bias of 0.5 K and a standard deviation of ± 0.8 K. The least accurate results were obtained in the DA algorithms with a bias close to -2.0 K and a standard deviation of almost ± 1.0 K.

Influencia del efecto de la humedad del suelo en la emisividad del infrarrojo térmico

The influence of soil moisture in thermal infrared emissivity is a known fact, but poorly studied in the past. An experiment for quantifying the dependence of emissivity on soil moisture has been designed. Six samples of superficial horizons of different Mediterranean soil types have been selected. Their emissivity has been measured at different soil water contents, using the twolid variant of the box method, whereas the gravimetric method has been selected for obtaining the soil moisture. As a result, the study shows that emissivity increases significantly when water content becomes higher, especially in sandy soils in the 8.2-9.2 μm range. A set of equations has been derived to obtain emissivity from soil moisture at different spectral bands for the analysed soil types.