undertaken 
| 305 mm focal 
le C-factor was 
1igh contrast 
e 
information 
19 to atmospheric 
id tilt. However, 
arp (about 0.02% 
the accuracy of 
of the flying 
. The error in 
of 13,400 m was 
gle lens (i.e. 15 cm 
points were 
animetric maps 
1:50,000 from 
t topographic 
racy falling 
ed too from the 
» 1977). 
rage by Landsat 
ite sensinge 
the land surface 
ing less *than 
about 45% was 
| of side-looking 
l weather 
ird advantage of 
+ and hence provide 
restry as in 
IR is either 10-20 m 
vison, the 
a is about 80 m 
erial camera 
nd wide-angle camera 
yted to be better 
provided the 
on the extent and 
and reduced time 
t will be appreciated 
altitude aerial 
ind that aerial 
nds and their 
- 1497 - 
shadows on any single photograph and not more than an average of 1% for the 
entire photographic coverage. 
Sierra Leone 
For Sierra Leone, the concept of high flight photography was attractive and 
offered excellent prospects. At least in theory, ,the country could be 
covered by high flight photography in about four days. Examination of black- 
and-white IR photographs of nearby Francophone countries showed that (despite the 
haze problems in the dry season) acceptable quality images can be obtained, 
which are superior to panchromatic black-and-white photography taken under 
hasy conditions, although of a lower resolution than black-and-white panchromatic 
photographs teken under non-hazy conditions (cf. Fig. 3a, 3b). Also, based 
on US experience of high altitude photography,products of acceptable quality 
for forest and land-use studies and with a high resolution, can best be 
obtained with colour IR film, provided a wide angle lens and not a super wide 
angle lens is used. 
At the time of planning the aerial photography for Sierra Leone (1975), 
consideration was also given to relying only on the 1951/64 panchromatic black- 
and-white photographs. Although these old photographs are of historical 
interest (e.g. for land-use dynamic studies, see Fig. 1) and provide some 
details used in studies of the geomorpu^'!ogy, hydrology, soil etc., their 
application to land resources survey in Sierra Leone was not practical for 
the following reasons: 
- Firstly, the thematic information relating to present vegetation 
and land-use of the country could not be satisfactorily extracted 
from old photographs (up to 24 years old at the outset of the 
project activities), but also due to the considerable time span 
between adjoining missions (up to 13 years). 
— Secondly, due to major changes in land-use, the identification of 
tie-in ground points would be tedious and sometimes impossible, 
while orientation problems in the field were bound to occurs 
— Thirdly, the total amount of photographs to be handled (3,600) together 
with the number of different photographic missions involved (at least 
8) would have made their systematic use awkward and time consuming, 
particularly when compared to a single coverage of high flight 
photographs consisting of 1,100 and 350 exposures only with wide- 
angle and super-wide angle cameras for scales of 1:70,000 and 
1:120,000 respectively. 
Concerning cloud-cover and length of season for aerial photography, daily 
detailed information on the seasonal distribution of rainfall was available 
from synoptic weather stations (e.g. at airports); and for the first time 
this type of information was combined with information on cloud cover obtainable 
by examination of the low-resolution NOAA imagery (Fige2).