How reliable is a satellite forest inventory

1998). The right side of the curve (A2, Tomppo et al. 1998) is the standard error of National Forest Inventory of Finland (NFI), based on systematic fi eld sampling. Both curves A1 and A2 decline as the reference area increases. The reason for the decline of the NFI-curve A2 is obvious because the number of sample plots in a large area is larger than that in a smaller one. For A1 the link to the number of fi eld plots is weaker, since in the multi-source method the connection between the number of fi eld plots involved in the computation and the area size for the estimation is not straightforward. Our hypothesis is that curve A1 is declining because variation of mean volume for small forest Previous Finnish studies have shown that at stand level, the standard error of volume estimates derived using high resolution (Landsat TM etc.) satellite data inventories is quite high. It is usually 40–60%, which from the viewpoint of practical forestry applications is too much (Paivinen et al. 1993; Hyyppa et al. 2000). High volumes tend to be underestimated and vice versa (Pussinen 1992). It has often been suggested, however, that for larger areas, the estimates are more reliable (see Tomppo et al. 1998, p. 641). In Fig. 1, curve A1 is based on empirical differences between multisource inventory and standwise fi eld inventories for various sizes of forest blocks (Tomppo et al. Silva Fennica 35(1) discussion papers