Retrieval of Biomass in Boreal Forest from Multi-temporal ERS-1/2 Interferometry

It is well known that C-band repeat-pass InSAR coherence can more accurately predict boreal forest stem volume than microwave radar backscatter. In this paper two boreal forest areas have been studied, one in Finland and one in Sweden. In spite of the small number of forest stands (approximately 40 stands at each site with mean area of 7 ha and stem volume range of 350 m/ha and 550 m/ha) a division in two halves has been made, one considered as reference stands and one as test stands. The observed coherence and backscatter values have been fitted to the interferometric water cloud model and a multi-temporal combination of up to seven InSAR pairs has been performed. For one of the test sites the accuracy of the best single pair is 36 m/ha (equal to 22 tons/ha), while a multi-temporal combination increases the accuracy to 21 m/ha (equal to 13 tons/ha). For the other test site the values are 91 m/ha, and 89 m/ha respectively. The results in this case are believed to be caused by differences between species distribution and also by weather conditions. We conclude that in some cases multitemporal InSAR is able to provide extremely good stem volume estimates.