Vicente Caselles Miralles

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.

Estimating surface energy fluxes using a micro-meteorological model and satellite images

The increasing interest of meteorological, climatic, and hydrological scientific communities in the different components of the surface energy balance, and particularly in the evapotranspiration, has encouraged the development of different micro-meteorological models for estimating surface energy fluxes at a local scale. Recent advances in satellite remote sensing techniques may allow the monitoring of these surface energy fluxes over extensive areas. However, most of the current models require in situ calibration or empirically derived parameters, which limit their operational application at a large scale. The objective of this work is to present a micrometeorological approach that can be operationally used together with satellite images to monitor surface energy fluxes at a regional scale. Firstly, we introduce the framework and details of the proposed micro-meteorological model, which is based on a two-source patch representation of the soil-canopy-atmosphere system. The feasibility of the model is explored at a local scale using data collected over two completely different ecosystems. On the one hand, data collected over a maize (corn) crop in Beltsville, Maryland, USA, during the 2004 summer growing season. On the other hand, data from an experimental campaign carried out in a boreal forest in Finland in 2002. Comparison of the results with ground measurements shows errors between 15 and 60 W m−2 for the retrieval of net radiation, soil heat flux, and sensible and latent heat fluxes in both sites.

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.

Fusión de las imágenes Landsat y micrometeorológicas para hacer un seguimiento de la evapotranspiración diaria a escala regional

The objective of this work is to show the operational applicability of a recently proposed model (S´ anchez et al., 2008) together with satellite images to monitor surface energy fluxes at a regional scale. In particular, we will focus on the retrieval of daily evapotranspiration because of the particular significance of this flux in the generation of precipitation or in agricultural water resource management. A detailed methodology to apply the Simplified Two- Source Energy Balance method to Landsat imagery is presented. The different surface cropland features are characterized from the CORINE Land Cover maps, and the required meteorological variables are obtained by interpolating the data of a network of agro-meteorological stations distributed within the region of interest. Finally, we show the application of the methodology to three different Landsat images covering the whole Basilicata region (Southern Italy). Maps of the different fluxes including the daily evapotranspiration are performed. Results are compared with some ground measurements, and an analysis is made taking the land use classification as a basis. An accuracy close to 30 W m 2 is obtained.