409
Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Development of a regional mapping system for the sahelian region
of west Africa using medium scale aerial photography
Steven J.Daus, Mamane Guero, François Sesso Codjo, Cecilia Polansky & Joseph Tabor
Resources Inventory and Monitoring section, Forestry and Land Use Planning project, Niamey, Niger
ABSTRACT: In response to an expressed need by the government of the Republic of Niger, a systematic mapping
procedure was developed to determine the surface area of forest lands in Niger. The objective was to develope
an approach suitable to: 1) the nature and value of the resources to be mapped and evaluated, 2) the available
source, or base, data, and 3) the technical capability of the Nigérien forestry personnel. The approach
included, regional stratification using LANDSAT MSS imagery, collection of ground data, and extrapolation of
this point specific data to the entire study area with the aid of a photo interpretation key developed for the
region.
RESUME: Selon des besoins precise par le governement de la Republique du Niger une procedure de la
cartographie systématique a était develope afin de determiner la superficie des terrains forestier au Niger.
L’objective était de établir et mis en oeuvre un system adapte a: la nature et valeur des ressources dresse,
les données de base disponible, et les capacitees techniques des cadres forestiers du Niger. L'approache
compris d'une delimitation regionelle a partir des images satellites LANDSAT, collection des données de
terrain et extrapolation des données des sites jusqu'au niveau de la zone d'etude entire aide par une clef
standard d'interpretation des photos aeriennes.
1.0 INTRODUCTION
The results presented in this paper are those from
work completed at the Resource Inventory and
Monitoring (RIMS) section of the Forestry and Land
Use Planning (FLUP) project. This project is funded
under the cooperative agreement #683-0230, between
the United States Agency for International
Development (USAID) and the government of the
Republic of Niger (GON). The primary aim of this
bilateral project is to establish within the
National Forest Service (NFS) of the GON a unit
capable of conducting resource inventories and
provide technical assistance regarding forest
management practices. This unit, the Office of
Technical Assistance (OTA), would contribute
information and technical assistance primarily at
the planning level within the GON.
The RIM section was established within the
structure of the FLUP project in order to: 1)
develop and implement resource inventory methods
appropriate to the various information needs of the
GON, and 2) train GON forestry personnel in the
planning and conduct of such inventories. It is
intended that the developed capability of the RIM
section, both the procedures instituted and the
personnel trained, will become an integral part of
the OTA.
2.0 SURFACE AREA OF FOREST LANDS: A PRIMARY
INFORMATION REQUIREMENT IN NATURAL RESOURCE PLANNING
AND POLICY
A primary information requirement when conducting
forest resource use and management planning is the
total area covered by forest vegetation, and it's
distribution within the area of interest. An
estimate of 14,000,000 hectares of forested land has
been put forward, but, this estimate was not based
on a systematic mapping or estimation procedure and,
as such, has not been incorporated in specific
forestry policy or management decisions. The
provision of this information was identified as one
of the tasks to be addressed by the FLUP project
and the RIM section, specifically.
3.0 DETERMINING THE SURFACE AREA OF FOREST LANDS
3.1 Selection of the basic approach
When considering the various alternative
procedures for determining the surface area of
forest lands in the Republic of Niger several
aspects are important. First of all there has been
very little precedential application of large area
inventories in the Sahel. Therefore, few
results exist with which to compare one approach
with another. A second consideration is the
combination of the relatively low economic value of
the resource and it's low concentrations. This
eliminates from consideration approaches which have
high costs per unit of area inventoried. A third is
the appropriateness of the approach in the context
of the capabilities of the GON forestry personnel
being trained. The approach cannot include or
utilize procedures which are highly complicated,
rely heavily on the judgement and experience of the
inventory specialists, or require equipment which is
difficult to operate and/or maintain in conditions
found in developing countries. Lastly, the approach
must maximize the use of work and/or source data in
existence and available.
The best approach to furnishing this information
to planning specialists is to produce a map which
shows geographical distribution, extent and condition
of forest lands. In arid land conditions, were the
subject resource is in a very low density and widely
distributed, and accessibility is a problem, a
proven method for generating such maps is to
interpret information from several levels of
remotely sensed data and combine it with limited
but highly representative, ground data. This
approach was used in Mali (PIRT, 1982) and
successfully produced terrain condition maps over
the very large study area. The specific approach
selected for application in the Nigérien situation
is characterized by the following elements:
- general stratification of the entire zone,
creating units of a certain minimum size and
homogeneity using LANDSAT satellite multispectral
scanner (MSS) data.
