502 
4.1. The h-Q approach 
Two parameters, h and Q must be determined, for each frequency. Surface temperature is obtained from 
METEOSAT. Near-surface soil moisture is supposed to be low for all targets on june-23 for no rains were 
identified during the previous days. A value of 0.02 was prescribed for soil moisture. Figures 6 and 7 show the 
derived h and Q parameters, respectively, at 19 GHz, with morning and evening data. The value of Q varies little 
from one target to another. There also seems to be little diurnal variation of this parameter. On the contrary, the 
h parameter presents a strong diurnal variation and depends on vegetation biovolume (represented by the 
variable height times NDVI in Figure 6). For example, at Tomelloso target (7), h varies from 0.633 in the 
morning to 0.384 in the evening, whereas Q is 0.340 in the morning and 0.395 in the evening. At 37 GHz, 
similar results are found. 
19 GHz — June 23 
Height x NDVI (m) 
Figure 6 - SSM/I-derived roughness parameter h versus the biovolume index Height times NDVI. 
19 GHz — June 23 
Height x NDVI (m) 
Figure 7 - As in Figure 6 except for Q.