NEE 
LEER 
  
  
i a A BR AS 
  
PHOTOGRAMMETRIC ENGINEERING 
part covered by aerial photographs. Firstly an 
estimate of the area of this forest was made 
by transferring the forest boundaries to a 
1:40,000 map. The timber volume of the 
limba was obtained by estimating the per- 
centage of the limba crowns compared with 
the total crown canopy. This was possible 
with a certain degree of accuracy as the limba 
crowns were in general easily identifiable on 
the photographs. Crown percentages were 
estimated within squares with a size of 7X7 
mm. indicated on an overlay. The choice of 
this size was based upon statistical treatment 
with different sizes. As the relation between 
crown percentage and the timber volume 
could be ascertained by terrestrial methods, 
the total timber volume for the whole area 
could be calculated. In total, 2100 photo- 
graphs were measured for crown density. The 
work was carried out by one forest officer 
with one assistant in the space of two years. 
Vegetation mapping: This work was ex- 
ecuted by the botanical department of the 
[.N.E.A.C. with institute headquarters in 
Yangambi (East-Congo). The final purpose is 
to obtain a vegetation map for the total 
Congo area, on a scale of 1 to the million. 
These maps are prepared in two different 
forms. On the first map the local forest dis- 
tribution is indicated, the second gives special 
information on local forest conditions. Both 
maps are based on information obtained 
from aerial photographs. 
In addition to these general maps, detailed 
maps are prepared of limited selected areas on 
a scale varying between 1:10,000 and 
1:50,000. For these aerial photographs are 
also used. Based on identified differences in 
the local composition of the vegetation, 
boundary lines are traced on the photographs; 
these lines in most cases coincide with differ- 
ences in soil and are afterwards transferred to 
a map on a suitable scale; this map is 
checked in the field. During this checking, 
special attention is paid to finding possible 
correlations between the composition of the 
vegetation, its soil type and its typical ap- 
pearance on the photograph. At the same 
time, boundary lines are checked. Based on 
the information obtained during the field 
work the final map is made. 
ETHIOPIA 
A predominant part of this empire has al- 
ready been covered by aerial photography. 
Based on information obtained by aerial re- 
connaissance the extent and distribution of 
the main forest areas over the whole country 
has been ascertained. More detailed forest 
16 
survey projects covering the most accessible 
and exploitable forest areas, based on the air 
photographs, have been planned for the near 
future. 
GHANA 
With regard to the application of aerial 
photographs in this country a distinction 
should be made between the savannah region 
in the North and the High Forest region in 
the South. 
Savannah region: Available topo maps in 
this region are small-scaled and provide only 
limited detail. Aerial photography is there- 
fore useful for Land Use Planning purposes. 
As no stereoscopic photo pairs were available, 
photo interpretation was made on single 
photographs. Such features as present land 
use could be identified, and future use could 
be planned on the basis of vegetation and 
topography. Erosion due to over-cultivation 
was rampant in some areas and the affected 
localities could be ascertained on the photo- 
graphs. Photographs also assist in selecting 
the boundaries of proposed forest reserves 
and give an indication of localities which ap- 
pear suitable for planting. In the event that 
further photography should be presented in 
the future, flying conditions are good for only 
2—3 months of the year. 
High Forest Region: Due to extensive cloud 
formation during most of the year, making 
exposures in this part of the country is ex- 
tremely difficult, except over the coastal re- 
gions. Only a few weeks in January or Febru 
ary at the most would be suitable for pho- 
tography, depending on the intensity of occa- 
sional dry desert winds from the North. 
Identifying tree species on the photographs 
would be difficult due to individual trees 
within species being deciduous at different 
times, and because of irregularity of flower- 
ing. Still, it would be worth-while to obtain 
more experience in general vegetation studies 
and in delineation of types. Without doubt 
such studies could be made considerably 
more accurate and detailed from aerial photo- 
graphs than by the terrestrial methods so far 
used. Certain species such as Avodire which 
sometimes occur gregariously should in such 
cases be distinguished on air photographs. 
Mahogany occurs in Ghana mainly in wet 
areas; therefore recognition of this species 
would be facilitated by restricting the areas 
in which the species 1s likely to be found, as- 
suming that these areas could be delineated 
on the photographs. 
Finally aerial photographs could be useful 
for controlling illegal farming in the forest