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- collection of detailed ground data related to
forestry at sites, whose selection was guided
interpretation of the LANDSAT image.
- identification of ground condition classes, which
are significantly different from the standpoint
of forestry, using data collected from the field
sites.
- define the relationships which exist between
forestry related ground conditions and their
appearances on the LANDSAT and aerial photos.
and
- use the appropriate imagery type as an implement
to extrapolate the limited ground data to the
area of interest.
3.2 The area to be mapped in order to determine
forest surface area
The study area for which forested area was to be
determined is shown in Figure 1. This zone was
defined in consultation with NFS planning personnel,
and in consideration of several aspects. This zone is
basically the arable portion of Niger, and as such,
has the highest capability for forestry production,
management related return, and potential degradation
from competing land uses. It is also the zone for
which several forms of base data are available,
including complete coverage by LANDSAT satellite
imagery and aerial photography.
Also shown in Figure 1 is the area where initial
test applications of the mapping procedure has been
completed. This area, indicated by cross-hatching
includes the two arrondissements of Mirria and
Matameye, and covers a total surface area of 12,000
square kilometers.
3.3 Products to be generated through the
development and application of the mapping procedure
The primary product requested by the NFS is a
series of maps, which show, for each arrondissement
in the study zone, where forest lands are located
and what is their extent. There are two basic
elements to these maps: 1) their format, and 2) the
information presented either by the map alone or in
association with a report. The format selected is a
line drawing map drawn on paper with a series of
codes to represent ground conditions. The map is to
have an associated report which explains the meaning
of each map code. The maps are to be completed at a
scale of 1/200,000 which will permit direct
comparison with the topographic map series available
for the area.
The second element is the identification of the
information to be presented by the maps and
associated reports. Forestry decisions rely very
heavily on physical conditions present at a specific
site as well as what vegetation does, or could,
occupy the site. These physical conditions include
the general land form and specific configuration of
terrain present at the site, and the soils
characteristics. These conditions were selected,
along with vegetation species composition and cover
percentage as the primary information themes of the
maps, and they were designated soil/vegetation/land
form (S/V/LF) base maps.
An additional product, of equal importance from
the standpoint of regional applicability, is the
photo interpretation key. This key was developed to
standardize the interpretation of the aerial
photography in the process of extrapolating the
site-specific ground data to the entire study area.
3.4 Data sources used in the mapping procedure
The primary data sources used in the mapping
procedure included: 1) LANDSAT MSS data in false
color infrared format (bands 4, 5 and 7) at a
reproduced scale of 1/200,000, 2) medium scale
aerial photography acquired at 1/60,000 and 1/70,000
in 23cm x 23cm, black and white, format, 3) the
1/200,000 topographic maps, and 4) ground data.
Figure 1. A map of the Republic of Niger showing the portion for which basic terrain elements are being mapped
and forest surface area determined. Also shown is the area in which applications testing has been completed.
In this zone, comprised of two arrondissements, Mirria and Matameye, the entire procedure was applied; from
initial stratification using the LANDSAT images to the production of the soil/vegetation/land form (S/V/LF)
base map and calculation of the forest type surface area.
