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Hyperspectral sensing of moisture gradients: the influence of recharge and discharge areas (MOISGRAD)

Projet de recherche S0/03/014 (Action de recherche S0)

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Project summary:

Within the framework of the CASI-SWIR measuring campaign 2002, and in preparation of the APEX programme, the Department of Hydrology and Hydraulic Engineering of the Vrije Universiteit Brussel (VUB) would like to submit a proposal for the hyperspectral remote sensing and analysis of moisture gradients in a valley area.
The background of this proposal is the importance of the determining and describing hydrological groundwater systems for the management and development of ecological values, especially in valleys of the river basin. At the ground surface, groundwater systems appear as infiltration and discharge zones; the latter are relatively wet because of the upward groundwater seepage, while the former are relatively dry. Groundwater discharge zones offer potential high nature values because of their constant moisture availability and their specific water quality. Valleys usually have a complex pattern of moisture gradients, caused by a complex interaction of regional groundwater flow with local influences of differences in soil and topography. Knowledge about infiltration- and discharge zones also forms the basis for sound, quantitatively and qualitatively, water management of groundwater systems. Current methods for the determination of discharge and infiltration zones use very data intensive numerical simulation models. Consequently there is a direct important need for repeatable, area covering, mapping possibilities for the determination of moisture gradients and more specifically discharge and infiltration zones.

The main objective of this proposal is to try out the best hyperspectral analysis method, using the CASI-SWIR data, for the known (based upon field and simulation data) moisture gradients in the Doode Bemde area in the valley of the Dijle River. An advantage of this study area is that it was the object of study of extensive hydro-ecological research during the last five years, for which a lot of field measurements as well as simulations have been carried out. This area is also very suited because of the hydro-chemical uniformity and clear, relatively constant, moisture gradients and associated differences in vegetation on a small scale caused by groundwater flow differences.

Simultaneously with the remote sensing, field measuring of soil moisture, groundwater levels and spectral vegetation characteristics of some key species (phreatophytes) will be performed. The required data for the geocoding and the atmospheric correction is already partly available and will be fully obtained during the field campaign.

The procedure for the hyperspectral analysis consists of two parts. During the first part, moisture gradients, from measurements and simulations and derived from maps of groundwater depth and of infiltration and discharge areas, will be statistically compared with individual bands, a combination of bands and multivariate derivatives. Using the available hydrological and vegetation knowledge, a physical explanation for the statistical best proxies will be determined. During the second part, a supervised classification will be performed for the moisture gradients, based upon the measured (field and remote sensing) spectral characteristics of the most important plant species (phreatophytes).

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