377
Microlight aerial surveys
land utili-
1 changes in
Lts can be
:y and des-
utilization
which this
testing of
; inventory
id inacces-
miques was
study. The
re analysis
field sam-
; constraint
information
during the
ising micro-
and oblique
lse in the
md existing
resents some
Lon types in
river and of
ie riverine
itterns bind
imate, the
rapacity of
situation,
variability
ind utiliza-
rrent cases.
demonstra-
Low a tho-
ition types,
after the
leralisation
rpes, with a
id use and
1 types is
: fieldwork
literature,
graphs. The
lich obser-
?asons, du-
The tec-
:t were the
;tation and
rraft as a
photography
photography
albeit in
urination has
additional
i as policy
ilation and
igy, soils,
/ity. Howe-
vays provide
ie national
ir riverine
r District,
list ribution
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-
