R Colombo

Use of semi-empirical and radiative transfer models to estimate biophysical parameters in a sparse canopy forest

Knowledge of the characteristics of the vegetation cover is of great interest due to its role in the mass and energy exchanges at the surface/atmosphere interface (e.g. water and carbon cycles). This study is part of DARFEM experiments, EU-funded HySens project (DLR), designed to provide a better understanding of the capability of airborne hyperspectral and directional observations to retrieve biophysical vegetation parameters. Different airborne hyperspectral data were acquired in late June 2001 on the experimental site, a poplar plantation belonging to CARBOEUROFLUX network, located in Northern Italy. An intensive field campaign was accomplished during the aerial survey to collect vegetation parameters and radiometric measurements. Leaf area index (LAI) and vegetation fractional cover (Fc), were retrieved from remote sensing data by statistical relationships with ground measurements. A radiative transfer model was used in direct mode to simulate and analyse the canopy spectral signature changes for varying overstory LAI and different understory conditions. In order to minimize the influence of the extensive understory vegetation on the relationship between spectral Vegetation Index (VI) and LAI, an optical index exploiting short wave infrared (SWIR) was evaluated. A comparison of different VIs performance is presented and relative advantages and drawbacks of SWIR exploitation are discussed.

Abiotic Stressors – Fire Hazard

Forest fires are worldwide recognized as one of the main factors affecting the forest ecosystem equilibrium, leading to direct and indirect impacts on the functions provided by forests (production, protection, wildlife, tourism, etc..). Forest fire ignition and propagation are closely linked to site-specific conditions: fuel characteristics, forest structure and composition, weather and topography. Within the MANFRED project, ERSAF was aimed to identifying potential evolution scenarios of forest fires danger due to climate change in the Alpine Space.

Flooded area estimation using radar images and digital elevation model

In this study were evaluated the utility of ERS-1 satellite imagery in conjunction with ancillary data for mapping the flooded areas of the November 1994 flood event occurred in Northern Italy. Two images were analyzed, one collected a month before the flood and the other one collected three day after the inundation. Two processing procedures and a visual interpretation were applied within a masked area extracted from the digital elevation model (DEM). Areal extent of flooded surfaces retrieved by the different methods were compared with the actual flood extension derived from field survey. Intermediate results showed that only a small fraction of the total inundated area was possible to estimated because of the time shift between flood and satellite passage. To overcome this limitation a procedure based on the integration of flooded areas as previously estimated by radar images, with a cost matrix calculated on the basis of the DEM was developed in a Geographical Information System (GIS) environment. This method allowed to map additional inundated areas amounting 96.7% of the actual flooded area. Result shows that even if radar data are taken some days after the inundation, they are still well suited to reconstruct flooded area when DEM is employed in the mapping process.

Integration of Stratigraphic Data, Pump Test and Geophysics for the Analysis of Shallow Unconsolidated Aquifers in West Africa and Identification of Suitable Condition for Manual Drilling

The study concerns part of the plain sector of Aosta Valley (NW Italy). The investigated area is located between the cities of Sarre-Gressan and Pollein-Saint Christophe and is characterized by the presence of hexavalent chromium in the main shallow unconfined aquifer. The pollution is probably related to the negative environmental effects induced by the industrial steel production that since 1915 is present over the area. Since 1990 the industrial area was subjected to a number of direct investigations aimed to assess the contamination intensity. A preliminary remediation activity has been developed in last decades but the contaminants have been still observed in the groundwater monitoring network. This study highlights the set-up of a groundwater conceptual and numerical model of the shallow aquifer aimed to better understand and analyze the transport dynamics of hexavalent chromium in the local aquifer. The simulation is performed using the specific finite element software Feflow for groundwater flow and mass transport modeling. The hydrogeological setting of this area is related to the different sedimentary glacial, lacustrine and fluvial processes which characterized the bottom of the Aosta valley during the Quaternary. The shallow 80m-width aquifer is constituted by sandy to gravelly deposits and presents rare silty lens while its bottom is characterized by a decametric lacustrine silty level. The main aims of the numerical model are to give a more unequivocal explanation of the origin of the contamination and to support the predictive analyses in order to design an efficient site remediation for soil and groundwater. This represents a fundamental task in order to preserve the safety of the public water uses supplied by the aquifer. The preliminary hypothesis about the source of contaminations are still uncertain and referred to different scenarios that have to be further investigated by comparing monitoring data and transient flow simulation conditions.

Evaluation of spatially distributed remotely sensed data to estimate hydrologically related parameters

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 & Gowards 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.