An Angular Thermal-Infrared Data Acquisition System to Validate and Improve Satellite Products
Niclos, Raquel1; Valiente, Jose Antonio2; Corell, David2; Barbera, Maria Jesus1; Estrela, Maria Jose1
1University of Valencia, SPAIN; 2Instituto Universitario Centro de Estudios Ambientales del Mediterráneo, SPAIN

Dedicated ground-truth experimental sites for thermal-infrared (TIR) radiometric measurements are commonly used to validate remotely sensed land surface temperature (LST) products. Requirements to elaborate more accurate LST retrieval algorithms, such as equations containing angular-dependent coefficients, and angular-dependent emissivity input data imply more detailed ground measurements at convenient equipped monitoring stations. Additionally, this type of ground observations can be used to better understand many land–atmosphere interactions such as the partitioning of latent and sensible heat flux or the monitoring of partly cloudy sky emission for the appropriate correction of LST by the sky reflected radiance. All these requirements lead to the convenience of using an specific device with automatic rotation to radiometrically scan sky and surface temperatures at different azimuth and zenith angles and to estimate hemispherical magnitudes by numerical integration.

Therefore, an autonomous system for field angular TIR data acquisition has been developed with the aim of being easily deployed at any traditional meteorological tower station. The device scans both hemispheres: sky and land, at several steps to attain remotely sensed temperatures by means of a single infrared radiometer. Apogee radiometers were selected to be included in the prototype not only by their reduced size and easy functioning but also by their measurement accuracies as proved in calibrations against NIST blackbodies. During the 2012 summer, a prototype of the device was deployed at a site with a fraction of vegetation cover close to one, particularly at an homogeneous and flat extensive ricecrop area called the Valencia Test Site extensively used in experimental CAL/VAL campaigns of satellite TIR sensors, e.g. ENVISAT-AATSR. The obtained angular TIR measurements have been analyzed and compared with LST products provided at different observation angles by several satellite TIR instruments, such as Metop-AVHRR, EOS-MODIS and MSG-SEVIRI.