Thermal remote sensing from Airborne Hyperspectral Scanner data in the framework of the SPARC and SEN2FLEX projects: an overview

The AHS (Airborne Hyperspectral Scanner) instrument has 80 spectral bands covering the visible and near infrared (VNIR), short wave infrared (SWIR), mid infrared (MIR) and thermal infrared (TIR) spectral range. The instrument is operated by Instituto Nacional de Técnica Aerospacial (INTA), and it has been involved in several field campaigns since 2004. <br><br> This paper presents an overview of the work performed with the AHS thermal imagery provided in the framework of the SPARC and SEN2FLEX campaigns, carried out respectively in 2004 and 2005 over an agricultural area in Spain. The data collected in both campaigns allowed for the first time the development and testing of algorithms for land surface temperature and emissivity retrieval as well as the estimation of evapotranspiration from AHS data. Errors were found to be around 1.5 K for land surface temperature and 1 mm/day for evapotranspiration

Quantifying the impact of cloud cover on ground radiation flux measurements using hemispherical images

Linking observed or estimated ground incoming solar radiation with cloud coverage is difficult since the latter is usually poorly described in standard meteorological observation protocols. To investigate the benefits of detailed observation and characterization of cloud coverage and distribution, a fieldwork campaign has been set up in order to collect data about cloud cover conditions and daily evolution to directly analyse their impacts on solar radiation fluxes. To do so, daytime hemispherical images have been collected at a very high frequency, simultaneously to ground measurements of solar radiation fluxes in a scientific station close to Lake NamCo, China. After calibration, one of the main tasks was the classification of those hemispherical images and the extraction of meaningful indices to describe the cloud cover, such as cloud fraction or cloud cover distribution. The classification is based on automatic detection of threshold on the red channel histogram. The results show that several cloud indices could be successfully derived from the hemispherical images, even if very thin clouds can be difficult to detect. The indices are then correlated to the measured solar radiation values and the impact of cloud cover on surface radiation fluxes were analysed. This analysis highlights that, more than the cloud fraction, the cloud distribution in the hemisphere is of importance when modelling radiation fluxes in the solar domain

Improved Surface Reflectance from Remote Sensing Data with Sub-Pixel Topographic Information

Several methods currently exist to efficiently correct topographic effects on the radiance measured by satellites. Most of those methods use topographic information and satellite data at the same spatial resolution. In this study, the 30 m spatial resolution data of the Digital Elevation Model (DEM) from ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) are used to account for those topographic effects when retrieving land surface reflectance from satellite data at lower spatial resolution (e.g., 1 km). The methodology integrates the effects of sub-pixel topography on the estimation of the total irradiance received at the surface considering direct, diffuse and terrain irradiance. The corrected total irradiance is then used to compute the topographically corrected surface reflectance. The proposed method has been developed to be applied on various kilometric pixel size satellite data. In this study, it was tested and validated with synthetic Landsat data aggregated at 1 km. The results obtained after a sub-pixel topographic correction are compared with the ones obtained after a pixel level topographic correction and show that in rough terrain, the sub-pixel topography correction method provides better results even if it tends to slightly overestimate the retrieved land surface reflectance in some cases.Geoscience & Remote SensingCivil Engineering and Geoscience

Correction of sub-pixel topographical effects on land surface albedo retrieved from geostationary satellite (FengYun-2D) observations

The Qinghai-Tibetan Plateau is characterised by a very strong relief which affects albedo retrieval from satellite data. The objective of this study is to highlight the effects of subpixel topography and to account for those effects when retrieving land surface albedo from geostationary satellite FengYun-2D (FY-2D) data with 1.25km spatial resolution using the high spatial resolution (30 m) data of the Digital Elevation Model (DEM) from ASTER. The methodology integrates the effects of sub-pixel topography on the estimation of the total irradiance received at the surface, allowing the computation of the topographically corrected surface reflectance. Furthermore, surface albedo is estimated by applying the parametric BRDF (Bidirectional Reflectance Distribution Function) model called RPV (Rahman-Pinty-Verstraete) to the terrain corrected surface reflectance. The results, evaluated against ground measurements collected over several experimental sites on the Qinghai-Tibetan Plateau, document the advantage of integrating the sub-pixel topography effects in the land surface reflectance at 1km resolution to estimate the land surface albedo. The results obtained after using sub-pixel topographic correction are compared with the ones obtained after using pixel level topographic correction. The preliminary results imply that, in highly rugged terrain, the sub-pixel topography correction method gives more accurate results. The pixel level correction tends to overestimate surface albedo.Geoscience & EngineeringCivil Engineering and Geoscience

Bilans radiatif et d’énergie dans un canyon urbain

Une campagne de mesures en climatologie urbaine a été réalisée durant l’été 2002 à Strasbourg dans le cadre du projet RECLUS. Parmi les sites de mesures, un échafaudage installé dans une rue a permis de réaliser des mesures continues de différents paramètres météorologiques sur quatre niveaux. L’objectif était de documenter les différents processus physiques qui interviennent dans l’élaboration du microclimat à l’intérieur d’un canyon urbain. Le présent article décrit les mesures et les premiers résultats obtenus en ce qui concerne les bilans radiatifs et d’énergie à l’échelle du canyon urbain

Bilans radiatif et d'énergie dans un canyon urbain

International audienc