shows some additional differentiation within the toich.
Within the high Toich two subunits show up. The high
Toich closest to the settlements show a dense vege
tation cover in late Wet season only whereas the part
further away has also some cover in mid wet season.
Some parts of the Toich near the swamp and parts of
the swamps (on the supervised image) appear to have
their own seasonality and correspond with the marshy
toich Typha-Leersia vegetation type of Yath (1984).
The supervised classification is practically a map,
it needs only a legend to be so. The multitemporal
image, however, shows not such clear boundaries and
requires some interpretation if a map is required.
Evaluating we may say now that the multitemporal
image is superior to both the supervised classi
fication and the false colour composite. The multi
temporal image might give a good land unit map on a
scale 1:250 000. In this type of flat, fluctuating
and flooding environment, it is also superior to
black and white aerial photography. However, on pro
ject scale where a land unit map of 50 000 - 100 000
is required, only aerial photography combined with
Landsat can give satisfactory results.
A main limitation to produce multitemporal imagery
is the availability of scenes of suitable season
within one year. In fact the used imagery set of
three dates in the only suitable one between 1972 and
today. For other parts of the Sudan and elsewhere no
such series might be found.
References
Gils, H. van & I.S. Zonneveld 1984. Vegetation and
Rangeland Survey. ITC, Lecture note, Enschede.
Mulder, N. 1982. Methodology of colour coding MSS
and other data. ISP Comm. Ill, Helsinki.
Yath, Y.A. 1984. Landscape-ecological survey of south
Kongor, Yonglei Sudan, MSc thesis, ITC-Enschede:
164 pp.
Mefit-Babtie 1983. Development Studies in the Yonglei
Canal Area. Final Report, 10 volumes. Khartoem/
Rome/Glasgow.
