Jes. Fransson et al., Stem volume estimation in boreal forests using ERS-1/2 coherence and SPOT XS optical data, INT J REMOT, 22(14), 2001, pp. 2777-2791
The use of spaceborne synthetic aperture radar (SAR) systems to estimate st
em volume and biomass in boreal forests has shown some promising results, b
ut with saturation of the radar backscatter at relatively low stem volumes
and limited accuracy of stem volume estimation. These limitations have moti
vated evaluation of more advanced methods, such as interferometry. The resu
lts presented in this study show that ERS interferometry, under favourable
conditions, may be used to estimate stem volume at stand level with saturat
ion level and accuracy useful for operational forestry management planning
in boreal forests. Five interferograms were analysed, covering a test site
located in the central part of Sweden with stem volume in the range Of 0-30
5 m(3) ha(-1). The best interferogram showed a linear relationship between
stem volume and coherence with a root mean square error (RMSE) of approxima
tely 26 m(3) ha(-1), corresponding to 20% of the average stem volume, throu
ghout the range of stem volume. No saturation was observed up to the maximu
m stem volume. However, the sensitivity of coherence to stem volume varied
considerably between the interferograms. Finally, four SPOT XS images were
evaluated and compared with the stem volume estimations obtained from the i
nterferograms, resulting in a relative RMSE of about 24% of the stem volume
, for the best case. The estimation of stem volume using coherence data,was
found to be better than optical data for stem volumes exceeding about 110
m(3) ha(-1). The statistical analysis was performed using linear regression
models with cross-validation.