5.2 Determining Biomass Production
Figure 4 shows a Terra MODIS image of the Nile River, which brings much-needed
water and silt to the Nile Valley, turning it into an oasis of agriculture and life. The
reason that the Nile River and some of the oases in Egypt are highly visible in this
image is because the river and springwater irrigate the soil and produce dense
vegetation that contrasts strongly with the surrounding arid land. At the apex of the
delta is Cairo, which appears as a gray-brown spot. The leaf-shaped patch of green
branching off the western side of the Nile is a depression that has been used as
irrigated agricultural area since 1800 BC.
Arid areas generally have sparse vegetation showing little biomass production.
However, where a freshwater spring emerges, biomass production is usually much
higher than normal. Aboveground biomass is usually evaluated by using one of
several vegetation indices [68, 69]. The most common index used is the NDVI,
which is expressed as the difference between the red and NIR reflectances divided
Fig. 4 True color Terra
MODIS image from August
23, 2003 of the Nile River
Valley with snakes in a
vegetated green line from
Lake Nasser in southern
Egypt to the edge of the
Mediterranean Sea, where it
widens out into a highly
productive, vast delta.
Credits: NASA
46
V. Klemas and A. Pieterse
Figure 4 shows a Terra MODIS image of the Nile River, which brings much-needed
water and silt to the Nile Valley, turning it into an oasis of agriculture and life. The
reason that the Nile River and some of the oases in Egypt are highly visible in this
image is because the river and springwater irrigate the soil and produce dense
vegetation that contrasts strongly with the surrounding arid land. At the apex of the
delta is Cairo, which appears as a gray-brown spot. The leaf-shaped patch of green
branching off the western side of the Nile is a depression that has been used as
irrigated agricultural area since 1800 BC.
Arid areas generally have sparse vegetation showing little biomass production.
However, where a freshwater spring emerges, biomass production is usually much
higher than normal. Aboveground biomass is usually evaluated by using one of
several vegetation indices [68, 69]. The most common index used is the NDVI,
which is expressed as the difference between the red and NIR reflectances divided
Fig. 4 True color Terra
MODIS image from August
23, 2003 of the Nile River
Valley with snakes in a
vegetated green line from
Lake Nasser in southern
Egypt to the edge of the
Mediterranean Sea, where it
widens out into a highly
productive, vast delta.
Credits: NASA
46
V. Klemas and A. Pieterse