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This paper will deal with the experiences gained from the rainy 
forest-region of West Africa. In that zone, the weather conditions 
seems to be the most complicated that a photographic expedition ever 
has to face. 
These extraordinary circumstances require special measures in the 
photographic field for what reason infrared film had to be used in the 
photographic process. But, unfortunately, this field is badly discovered 
by experiments in the technics, thus making this advanced application 
of the aerial photography still more involved. 
But apart from a short introduction of the general conditions the 
primary aim of this paper is to render a statement of the experiences 
regarding the reconnoitring and measuring of landmarks used as con 
trol points of the map. In the dense bush of West Africa well-defined 
landmarks are of rare occurence. But this paper will also deal with 
another type of landmarks of great interest to the archaeologists. 
2. Meteorological Conditions 
In order to facilitate the understanding of the problems that will face 
people who have to carry out an aerial photography in the Tropics, I 
would like shortly to give an idea as to the climate of West Africa and 
particularly of Liberia. Especially the temperature and the humidity 
will cause the aerial photographer troubles. 
The rainy forest-region of West Africa has two distinct, climatic 
seasons of approximately six months each: a dry and a rainy season. 
The dry season, from November to April inclusive, is ushered in and 
finished off by violent thunderstorms. Marked by a rapid drop of 
precipitation, this season is characterized by long periods with a clear 
sky, most typical during October—December. January and February 
are the driest months, but never without some rainfall. At that time, 
north winds bring high-pressure air, coldish, reddish and dusty, from 
the Sahara desert — called the »Dry Harmattan». The rainy season, 
extending from May to October, is characterized by heavy rains, but 
there is always some sunshine. In July and August, the precipitation 
often drops causing a condition known as the »mid-dry» season. 
Although Liberia lies in the equatorial belt, the temperature is not 
extreme. It is more or less uniform throughout the year. The tempera 
ture ranges from 20 to 37° C. The range of humidity is on an average 
78 % during the dry season and 82 % during the rainy season. 
3. Vanishing of Landmarks 
When LAMCO, the Liberian American-Swedish Minerals Com 
pany, in a joint venture with Bethlehem Steel Co. had to face the claim 
for an up-to-date mapping for the Nimba Mining Project it was 
evident that the company had to consider a very important problem.