Research Methodology - Historical Land Use/Land Cover Classification Using Remote Sensing - page 90

Fig. 5.19 The distribution of the training fields used in the spectral measurements

The total radiometric readings numbered 2,669 measurements that represented
103 training-fields of different crops (Fig. 5.19 ).
These displayed the values of the spectral reflectance as spectral signature for
each crop, within the wave-lengths from 35 to 2,500 nm and with a spectral
interval of 1 nm for the crops in the study area through their growth stages,
allowing for a temporal succession of 15 days between the various readings, from
planting and germination until harvest. The spectral results that represented the
winter crops included wheat, barley and sugar beet. For example, the training
fields of wheat in Arraqqah Province were made up of 35 fields (Fig. 5.20 ).
Figure 5.21 illustrates the bond between the spectral responses of the irrigated
wheat during 10 different growth stages and the characteristics of the eight bands
of ASTER. It is clear that the reflectance potential is greatest at the third band
among the whole growth stages, with the exception of the time period from 04.12
to 23.01 in the study year, where the reflectance of the soils prevailed.
Figure 5.22 illustrates the change in the spectral response of the irrigated wheat
in relation to the eight spectral ASTER-bands among the 10 various growth stages.
After analyzing the various spectral responses of the different winter crops in
the study area, the appropriate date for separation between the three irrigated major
strategic crops (wheat, barley and sugar beet) was determined in the first days of
May. In addition, sugar beet was found to have another separation date in mid-
June, when the other two crops (wheat and barley) were harvested or had a dry and
yellowish appearance (Fig. 5.23 ).
Secondly, the spectral results that represent the major summer crops included
cotton, corn and watermelon. Figure 5.24 illustrate the spectral response of each
crop. The third spectral band of the ASTER-sensor had the greatest sensitivity and