Tal Svoray 
  
Coefficient of determination of 0.9 has been achieved 0.60 7- 
for points representing eight relatively homogenous 
plots of herbaceous vegetation. When considering the 
complex conditions of the study area, this level of 
accuracy is satisfactory. However it is important to predicted . 
note that in two cases the predicted biomass values | 
  
   
      
   
have suffered considerably high overestimation. The 0:20 | 
two points were examined carefully but we could not e 
find any particular environmental condition, which we... 
may explain their abnormality. This observation will 0.0 010 020 030 040 050 060 
be more closely examined with a larger database. If 
: : Measured 
the analysis of a larger database will show the same 
trend, the overestimation could be normalized with an Figure 6. The relationship between predicted and 
empirical factor. The case of heterogeneous plots was measured herbaceous vegetation green biomass 
much more complex, involved more factors and thus [Kg m™] in homogenous plots. 
yields less strong relationship (coefficient of 
determination of 0.79). The case of heterogeneous 
plots differs from the case of homogenous plots in two 
major aspects: first, the range of herbaceous 
vegetation green biomass in the case of the 
heterogeneous plots is much more limited obviously 
as other vegetation formations exist in plots; and 
secondly, there is lack of consistency in 
overestimation in the case of heterogeneous plots: 
over and under estimations seem to be more or less 
equal. To summarize this part we may say that it is 
Predicted 
well believed that albeit the reduction in the 0.00 0.05 0.10 0.15 0.20 0.25 
significance of the relationship between the 
herbaceous green biomass and ERS-2 SAR 
backscatter in the case of heterogeneous plots, it is 
still a promising result which may be well improved Figure 7. The relationship between predicted and 
with the determination of more precise coefficients measured herbaceous vegetation green biomass 
with increasing the database and more attemptions to [Kg m™] in heterogeneous plots. 
determine best initial points. 
Measured 
5 SUMMARY AND CONCLUSIONS 
Multi-temporal characteristics of the ERS-2 SAR backscatter from four Mediterranean vegetation formations were 
studied in the semi-arid zone of Israel. Significant differences were found between the multi-temporal backscatter 
signatures of herbaceous vegetation and woody plant formations. The application of semi-empirical backscatter model 
in conjunction with cover fractions derived from Landsat TM data enable to adapt successfully the water-cloud model 
to the Mediterranean environment. Significant correlation was observed between the predicted and estimated values of 
herbaceous green biomass in homogenous and heterogeneous (mixed) plots. These results imply on the potential of 
the ERS-2 SAR data for the estimation of herbaceous vegetation green biomass in wide regions. 
ACKNOWLEDGMENTS 
We wish to thank the Forest Authority (Keren Kaiemet Leisrael) and the Ministry of Agriculture of Israel for 
financing this project. 
REFERENCES 
Attema, E. P. W. & Ulaby, F. T., 1978, Vegetation modeled as a water cloud. Radio Science Vol. 13, pp. 357-364. 
Laur, H., Bally, P., Meadows, J., Sanchez, B., and Schaetter, E., 1997, ERS SAR Calibration — Derivation of the 
Backscattering Coefficient Sigma-Nought. In ESA ERS SAR PRI products. Document No: ES-TN-RS-PM-HL09, 
ESA web site http://uranus.esrin.esa.it/eeo/lft/ESC2. 
  
Prevot, L., Dechambre, M., Taconet, O., Vidal-Madjar, D., Normand, M., and Galle, S., 1993, Estimating the 
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