International Archives of Photogrammetry and Remote Sensing. Vol XXXII Part 7C2, UNISPACE III, Vienna 1999 
40 
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I5PR5 
V®y 
UNISPACE III - ISPRS Workshop on 
“Resource Mapping from Space” 
9:00 am -12:00 pm, 22 July 1999, VIC Room B 
Vienna, Austria 
I5PR5 
presented in Fig. 1. Traditionally, crop yields are presented in 
physical weights per unit area (kg/ha), but under water short 
conditions, it is recommended to express the yield per unit of 
water evaporated (kg m' 3 ). The diagram in Fig. 1 reveals that 
the grain yield of wheat varies between 0.4 to 1.6 kg m' 3 of 
water evaporated. Evaporation has been selected as it reflects 
the crop response to all water resources, including precipitation, 
irrigation and groundwater by means of capillary rise. 
Moreover, water that evaporates leaves the soil-vegetation 
system irreversibly, and can not be recaptured. Evaporation 
needs therefore to be utilized with the maximum effectiveness 
feasible. This examples demonstrates a factor 4 difference 
between the lowest and highest productivities, which implies 
that resource management has considerable room for 
improvement, if done carefully. Especially the combination of 
water with fertilizers, solar radiation and soils seems an 
important way forward to increase the effective use of scarce 
water resources. 
evaporation at field scale is 10 to 20%, for a number of fields 
the error reduces to 10% and for a catchment of 25,000 ha, the 
error is usually less than 5%. 
An example of satellite interpretation of evaporation is 
presented in Fig. 2. A national map with a comprehensive river 
system and complex hydrology viewed by a single raster map is 
the first endeavour. The date of February 17 reflects the wheat 
season in the Punjab Province, Pakistan’s breadbasket area. The 
image reveals that the Sindh province taps meager water 
resources from the Indus system. This situation gradually 
changes throughout the irrigation season (not shown): large 
tracts of the Sindh Province (Hyderabad) are cultivated with 
cotton and sugarcane during spring, whereas the September 
image shows large tracts of paddy with a high consumptive use 
(up to 4 mm d 1 ) in the Larkana area. 
3. MONITORING THE NATURAL RESOURCES IN 
SPACE: A CASE STUDY IN PAKISTAN 
Biomass growth (kg/ha/day) and the actual evaporation 
(m 3 /ha/day) can nowadays be interpreted using physically based 
interpretation algorithms using the spectral radiances measured 
from space. The extent of ground truth data is very much 
limited, and almost excluded in the operation of these 
algorithms. A case study to diagnose the water use patterns in 
the entire Indus River System was initiated to quantify the 
process of irreversible water depletion from river basins 
(Bastiaanssen et al., 1999). As one of the largest contiguous 
irrigation systems in the world, the Indus Basin irrigates more 
than 16 million ha of land. Pakistan’s climate is arid, with a 
monsoon from July through to September. Wheat and fodder are 
the dominant crops during the dry rabi (winter) season. Among 
others, cotton, rice and sugarcane are produced during the wet 
kharif(summer) season. 
The study is based on a series of 20 National Oceanic 
Atmospheric Administration - Advanced Very High Resolution 
Radiometer (NOAA-AVHRR) images acquired during 1993-94. 
The AVHRR images have first been geometrically corrected to 
remove effects from the earth’s curvature. Thereafter, the 
separated channels of the AVHRR have been corrected for 
atmospheric perturbations on the spectral radiances. First levels 
of derivable products from AVHRR’s spectral radiances are 
surface albedo, solar radiation, vegetation index and surface 
temperature. This data is applied to obtain radiation and energy 
balances 
at a Fig. 2 Aerial patterns of actual evaporation across Pakistan on February 17, 1994. White is zero evaporation and black 5 mm d' 
spatial 
resolution of 1.1 km. The actual evaporation was estimated with 
the Surface Energy Balance Algorithm for Land (SEBAL) being 
developed by Bastiaanssen et al. (1998). Space limitations allow 
only the mention of evaporation calculated from the 
instantaneous evaporative fraction, A, and the daily averaged 
net radiation, R n2 4. Generally, the error of a single day actual 
Chlorophyll absorbs most incoming solar radiation in the red 
range between 0.6 and 0.7 pm and reflects radiation in the 0.75 
to 0.9 pm near-infrared range. Thus composites of red and