scale analogue spatial data bases on natural resources
since the eighties on a national level, e.g. Plan National
d'Aménagement du Territoire (PNAT, Senegal), Projet
d'Inventaire des Ressources Terrestres (PIRT, Mali). On
the other hand regional to subregional approaches to
monitoring specific regions of interest in a more holistic
and comparative manner are rare.
Especially Sahelian regions of high ecological and
economic value need permanent observation via medium-
to-high resolution spaceborne remote sensing.
Sophisticated methods of collection, integration,
maintainance and analysis of spatial data have to be
adjusted to regional and local environmental action plans.
Harmonized and standardized data of specific networks
of regions have to be integrated with national and
international environmental action plans. Some pilote
activities are in progress, e.g. the programme for
managing the environment locally in Sub-Saharan Africa
(MELISSA) of the World Bank Africa Region Environment
Group or the subregional action programme (SRAP) of
CILSS, IGAD, SADC, UMA and UNSO (UNSO, 1992,
‘SADC et al, 1994, CILSS/PNUE, 1996, Prévost et
Gilruth 1997). Nevertheless the efficiency of the
comparative analysis of landcover and landuse change in
seriously affected regions of Sahelian Africa is still at a
low level.
2. REGIONALIZATION OF REMOTE SENSING AND GIS
IN THE SAHEL
Approaches to large-to-medium scale monitoring of
Sahelian regions have to combine field work,
interpretation of aerial photography and classification of
satellite imagery with informations extracted from
topographic maps, thematic maps and statistical surveys
(figure 1).
Field mapping of soils and vegetation has to focus on
keywords like taxonomy, soil erosivity, diversity,
structure both horizontally and vertically and interactions
with patterns of human impact on herbaceous and
ligneous vegetation strata (Blanck et Tricart, 1991).
The (semi-)detailed analysis of vegetation structure is
supported by the interpretation of multitemporal aerial
photography. Medium scale mapping of vegetation
functional types and of regional landcover units is
contributed by the analysis of satellite imagery.
Integrated approaches to terrain analysis and remote
sensing for desertification monitoring benefit from a
specific variety of sensors with different spectral, spatial
and temporal resolutions. Topographic and thematic
maps with project-driven or nation-wide coverages are
available in scales of 1:200000 and smaller.
Local to regional dynamics of impact patterns have to be
analysed. The visual stereoscopic interpretation and the
computer-assisted multi-spectral as well as textural
image classification of remotely sensed data support
multi-thematic cartographic models of Sahelian regions
by creating spatio-temporal landuse and landcover data
layers. Modeling regional dynamics of degradation and
desertification is above all supported by time series of
remotely sensed data. Topo-chronological maps of land-
cover change since about 1950 (aerial photography) and
1972 (satellite imagery) respectively can be established
(Csaplovics, 1990, Csaplovics, 1992), (figures 2,3).
The impact of the severe droughts in the West African
Sahel from 1968-1973 and 1983 to 1985 as well as the
increase of anthropozoic pressure on the Sahelian
grasslands can thus be documented by remotely sensed
data analysis. Multi-temporal maps of the degradation of
soils and vegetation will help to establish GIS data bases
of the landcover status and change of Sahelian regions.
Case studies improved the presented design of a
complex methodology for multi-temporal regional
investigations. The regions of the river Niger are key
regions of the West African Sahel in geographical and
hydrological terms as well as in terms of specific socio-
economic and socio-ecological impact. The inter- and
intrarelations of environmental impact patterns and their
effects on destabilization are documented and analysed
by the fusion of multitemporal earth observation data of
different sensors and in different scales and by
integrating map and ground truth informations via GIS-
technology (Csaplovics, 1996, Csaplovics 1997).
3. OUTLOOK
Local and regional planning for restoration and
sustainable development depends on powerful tools for
monitoring and modeling the dynamics of landcover
change. Remote sensing and GIS facilities have to be
developed in terms of appropriate technologies. Providing
regional planning with high-quality spatio-temporal geo-
informations increases the efficiency of substituting
information for non effective energy by matching
resources to specific requirements
Regional centers of remote sensing and GIS have to be
established in the Sahelian countries. Plans to launch
small non-profit remote sensing platforms with on-board
sensors designed for medium (to large) scale monitoring
of Sahelian regions should be executed as soon as
possible. Fast accessibility to and low prices of remotely
sensed data have to be guaranteed. Connecting regional
GIS working units with national and global networks
should increase the awareness of the correlation of
processes of local, regional and continental variations of
degradation and desertification (figure 4).
Regional planning needs up-to-date environmental
information systems for approaching real time evaluation,
prediction and prevention. Main support is contributed by
establishing operationalized methods of data exchange at
a multi-regional level. Networking facilitates cooperation
and coordination of monitoring and planning at
subregional, regional and international levels in both a
horizontal and vertical direction. The success of
subregional and regional initiatives depends on finding
the knot to connect high-tech internet tools with
concepts of low-cost appropriate technology as well as
with concepts of participation.
REFERENCES
Blanck, J.P., Tricart, J., 1991. Quelques types de
dégradation des milieux sahéliens. Zeitschrift für
Geomorphologie. Supplement-Band 83:17-21.
CILSS/PNUE, 1996. Systèmes d “information
environnementale dans la sous-région sahélienne.
Rapport final.
Csaplovics, E., 1990. Monitoring desertization dynamics
in the Canal du Sahel region (Mali) using Landsat TM and
MSS data. In: Coulson MG (ed) Remote sensing and
global change, Proceedings of the 16th Conference of
the RSS, Swansea, pp. 31-40.
104 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
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