<title>Evaluation of spatially distributed remotely sensed data to estimate hydrologically related parameters</title>

Abstract

In this study spatially distributed and semi-distributed hydrological-related parameters, such as the Normalized Difference Vegetation Index (NDVI), Leaf Area Index (LAI), albedo and surface temperature, were evaluated by means of multitemporal optical remotely sensed data and field radiometric measurements acquired in different hydrologic conditions of the Virginiolo catchment (Italy). Land use land cover classifications were performed using Landsat Thematic Mapper (TM) data of spring and summer seasons. Digital counts were converted into calibrated radiance values and, after atmospheric correction, reflectance measurements were obtained. To estimate the spatially distributed LAI values and their changes related to the modifications of environmental and agrometeorological conditions within the catchment area, an empirical relationship between NDVI and LAI for Mediterranean areas reported in literature was used. Broadband surface albedo was estimated from spectral reflectance measurements obtained from the TM narrow bands following Brest & Goward's approach, and surface temperature was derived from the TM channel 6. Radiometric and thermoradiometric measurements, collected over selected fields were used to estimate the same hydrological-related parameters. When satellite images are not available, due to the presence of clouds, such parameters may be used in a semi-distributed hydrological modeling.