377 
Microlight aerial surveys 
land utili- 
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Figure 2. Tana River courses as derived from Landsat 
imagery and topographical maps. 
of settlements, nor is a breakdown presented for 
ethnic groups which claim different identity from the 
Pokomo, Orma and Somali, which are recognized in the 
census. 
Existing aerial photo coverage consists of different 
sets of photographs of different scales, years and 
seasons, neither of which provides a full coverage of 
the study area. Even the largest scale photography 
(scale 1 : 20,000) provides too little detail to 
enable a satisfactory interpretation of the traditio 
nal land use patterns, given the limited contrast 
between natural and man-made features, such as agri 
cultural fields or shamba's and settlements. 
No spaceborne earth observation missions have as yet 
been able to produce good coverage of the southern 
part of the study area, due to a persistent cloud 
cover. Landsat imagery does however provide good 
insight in the different broad geographic zones in 
the study area. From this Landsat imagery, changes in 
the braiding and meandering river course could well 
be observed and mapped. This provides information on 
the (horizontal) dynamics of the river in the diffe 
rent zones (see figure 2). 
In general it can be concluded that very little 
information exists in literature on the inhabitants 
of the riverine zone and their use of these lands. 
The existing information is at least not specific 
enough to provide more than a very general impression 
of the area as a whole, while detailed information is 
available of the implemented, planned or abandoned 
irrigation schemes in the area, such as the large 
scale schemes of Bura, Hola and Tana Delta, and the 
smaller schemes, often at village level, at 8 loca 
tions along the river. 
2.3 
The riverine belt is a vast and rather inaccesible 
terrain, due to the presence of forests, thickets, 
swamps and inundations. When data collection had to 
be based on ground based observations only, a manpo 
wer and time consuming fieldwork would have to be 
undertaken which required a budget far beyond the 
budget of the study. When also the fact is taken into 
account that the existing aerial photography provided 
no satisfactory information on land use and the dyna 
mics therein (seasons, inundations, etc.), it is 
clear that new ways and means had to be found to 
collect the required data. 
Aerial photography forms a powerful tool in such an 
inventory, so various alternatives to produce this 
photography have been contemplated. 
The requirements for aerial photography in this exer 
cise can be summarized as: 
- data have to be collected in various seasons 
- data have to be collected at low waterlevels as 
well as during floods, which on many locations 
last shorter than two days 
- besides some indication of scale no metric accuracy 
is required for the photography 
- the data had to contain information so detailed as 
to enable an interpretation of crops, settlements, 
etc. 
These requirements lead to the conclusion that an 
aircraft and crew should be on standby in the study 
area to produce the required aerial photography, 
during several periods, totalling about three months. 
This makes the exercise extremely costly when normal 
aerial survey aircraft equiped with photogrammetric 
23 cm camera's would be used. 
Small format aerial photography (35 mm or 70 mm 
negative format) is a technique well known in Kenya 
and several light aircraft based in Nairobi could be 
equipped for the purpose. However due to the remote 
ness of the study area and the required very flexible 
survey set-up in space and time, the use of one of 
these configurations still is too costly (especially 
through the long standby periods, and the on and off 
flying to the study area), where no aircraft services 
can be provided). 
Microlight aircraft are a new but rapid development 
in aviation. The characteristics that distinguish 
them from other aircraft are the low cost in pur 
chase, the relative simplicity of microlight flight 
and the fact that many types can be transported on 
top of a car or on a trailer, from which they can be 
assembled rapidly. 
When these aircraft aircraft are equipped with came 
ra's and flying instruments, they may have a poten 
tial as a surveying tool in this study, which is 
worth to study, given the attractive features of such 
a system in view of the study requirements: 
- the system can be operated by a teammember who has 
undergone a brief training on the aircraft 
- the system can be used where and when necessary and 
is at immediate disposition of the team 
- no airfields are required for landing and take-off: 
The many open spots, car tracks, lake shores, etc. 
permit a safe and also efficient operation, since 
the flying distance to a study area may be very 
short, but a very time consuming affair by road. 
2.A Aircraft, camera and film 
The microlight used in this project is an Eagle 215B 
of American Aeolights Inc. with a Cuyuna single cyli 
nder 215CC two stroke engine. In Figure 3a the air 
craft is illustrated. 
The Eagle is a relatively old design in microlights. 
It is reputed as one of the safest designs. In compa-