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Analysis of Landcover Dynamics in the Niger Inland Delta using MERIS Full Resolution Data

Ralf Seiler(1) and Elmar Csaplovics(1)

(1) Technische Universität Dresden, Helmholtzstrasse 10-13, 01062 Dresden, Germany

Abstract

Located in the western Sahel of Africa, between 13°30' and 17° north and 2°30' and 5°30' west, the Niger Inland Delta names one of the largest floodplain in the world. The geographic term "Niger Inland Delta" stands for a vast, extremely flat area of some 10.000 km² extend, which is annually inundated caused by the water of the Niger-Bani Riversystem. In contrast to its semi-arid environment, the delta's ecology can be described as a mosaic of permanently, periodically and episodically flooded areas. Their extend varies both in scale and time due to irregularities of amount as well as seasonal distribution of the annual rainfall in the catchment areas and the resulting water supply contributed by the river system.

The Inland Delta is dominantly covered by irrigated fields or grasslands during flood and post-flood months (October to January), while most of the photosynthetically active vegetation withers during the rest of the year. Interaction among pre-flood, flood and post-flood conditions strongly affect the patterns of landcover in and around the delta. But Vegetation cover density remains low even during the flood period with exception of some parts of the central Delta.

This study analyses the intra-annual dynamics as well as changes in landcover due to variation in the extend of flooding between individual years by interpreting at least 5 full resolution data from MERIS sensor of ENVISAT for each growing season over the period from 2002 to 2005. As the dynamics of Landcover can be described mainly as changes in vegetation cover density, we applied Vegetationindizes (VI) as parameter to describe these changes. To overcome well known problems with NDVIs dependency of illumination and viewing angle, background signal (soil brightness) and changes in humidity, we used the MGVI (GOBRON et. al) and MTCI (Dash et. al.) as possible Indizes to derive more sophisticated biophysical information in addition to the classical NDVI.

Due to the sparse vegetation layer, different soil types influence the remotely sensed signal significantly. We therefore integrated information about soil brightness that was derived from a LANDSAT ETM+ dataset to our analysis.

Multi-temporal datasets of each VI were classified in 2 different joint approaches to separate the object categories along their intrinsic radiometric-temporal behaviour. At first we classified all datasets using a k-mean ISODATA algorithm and secondly we applied Fourier Transformation to filter the main spatio-temporal features from the datasets.

This paper aims to show the potential of MERIS full resolution data to monitor the dynamics in landcover for a wetland in semi-arid environment. We compare suitability of different VI as well as different classification approaches. As a result of our analysis we obtained a detailed mapping of the spatio-temporal landcover patterns of the Niger Inland Delta for the period 2002-2005.

REFERENCES: DASH, J., CURRAN, P.: MTCI - a new MERIS Terrestrial Chlorophyll Index. Proc of the MERIS User Workshop, Frascati, Italy, 10-14 November, European Space Agency. GOBRON, N., MÉLIN, F., PINTY, B., TABERNER, M. AND VERSTRAETE, M. M., 2003: MERIS Global Vegetation Index: Evaluation and Performance. Proc of the MERIS User Workshop, Frascati, Italy, 10-14 November, European Space Agency SP 549. OLSSON, L., EKLUND, H., 1994: Fourier Series for analysis of temporal sequences of satellite sensor imagery. Int. Journal of Remote Sensing 15, pp. 3735-3741

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry