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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
  
purpose of recognition, we need to describe the properties of 
pixels or groups of pixels. 
2. THE STUDY AREA 
The Okavango delta in northwestern Botswana is an extremely 
complex and dynamic wetland ecosystem. The increasing water 
demand from basin sharing countries (Angola, Namibia and 
Botswana) puts the resource under growing pressure and poses 
complex management problem. Water is a precious and 
important resource for all three riparian states of the basin. The 
demand for water is growing due to rapidly rising population 
and associated activities like irrigation and power generation. 
The Okavango delta (Figure 2), variedly termed as “the jewel” 
of the Kalahari (Ross, 1987), Africa’s “Wetland Wilderness” 
(Bailey, 1998) and so on. It is the last remnant of the ancient 
great Makgadikgadi Lake, which was formed by the Kalahari 
sands about three million years ago (Ross, 1987). The delta is a 
large alluvial fan and experience annual flooding. It consists of 
a series of permanent river channels, semi-permanent drainage 
channels, lagoons, islands and floodplains that link up and then 
separate again during the course of an annual flood. The delta 
has a very low gradient. From Mohembo to Maun with a 
distance of 240 km, there is roughly 1m height variation for 
every 4 km distance (Figure 2). 
x Mohembo 
  
   
  
  
Figure 2. The Okavango delta as seen from Landsat 7 ETM+ 
(54,2 combination) image, April 2000 
The Delta is located in a semi-arid region which experiences 
wide variations in flooding over permanent swamps, seasonal 
Swamps and other intermittently flooded areas. The permanent 
swamp covers approximately 6,000 km’, while the seasonal 
swamp varies between 4,000 and 10,000 km?. Water depth in 
the permanent swamps averages 1.5m (UNDP, 1977), while in 
the seasonal swamps it is generally less than 1m (McCarthy e/ 
al., 1998). 
297 
The river and the delta serve as major source of fresh water to 
the people of the basin area. The Okavango is one of the few 
large rivers in the world without notable man-made 
developments and that has so far remained relatively pristine. 
3. DATA AND METHODS 
3.1 Data 
The primary data used in this study were SPOT 5 High 
Resolution Geometry (HRG) sensor image acquired on 12 
November 2002 and Landsat 7 Enhanced Thematic Mapper 
Plus (ETM+) sensor image acquired on 28 March 2001. The 
other data used are 1:50,000 scale topographic maps and GPS 
measured ground control points. Both SPOT 5 and Landsat & 
images are taken during dry seasons. Figure 3 shows the scene 
location of SPOT 5 and Landsat 7 over the Okavango delta. 
The SPOT 5 satellite was launched on May 2002 with Araine 4 
rocket and put on polar sun synchronous orbit at an altitude of 
832 km from earth surface, while the Landsat 7 satellite was 
launched on April 1999 with Delta rocket and put on polar, sun 
synchronous orbit at an altitude of 705 km from earth surface. 
Both SPOT 5 and Landsat 7 satellites orbit the earth in sun- 
synchronous mode at an inclination of 98.2? and 98° degree 
respectively. 
Landsat 7 
175/073 
174/073 
SPOT5 
118/388 
175/074 174/074 
A 
Figure 3. Landsat 7 ETM+ and SPOT 5 HRG scene location 
over the Okavango delta 
SPOT 5 HRG sensor provides multispectral (10m resolution in 
band 1-3 and 20m resolution in band 4) and one panchromatic 
band (Sm resolution) image. Each SPOT 5 HRG scene covers a 
ground area of 60 km x 60 km (nadir viewing). The HRG is an 
optical/near infrared sensor (Table 1), which is based on High 
Resolution Visible (HRV) and High Resolution Visible and 
Infrared Sensor (HRVIR). Both HRV and HRVIR are 
optical/near infrared CCD (pushbroom) imaging radiometers 
carried on SPOT-1 to -3, and SPOT- 4 respectively. The two 
HRG instruments aboard SPOT 5 are the main imaging 
instruments. They provide panchromatic (black and white) 
imagery at a resolution of 2.5 or 5 metres and multispectral 
(colour) imagery at a resolution of 10 metres.