Improving Inventory Volume Estimates by Double Sampling on Aerial Photographs

Abstract Data from extensive timber inventories of 12 counties in western and central Washington were analyzed to test the relative efficiency of double sampling for stratification as a means of estimating total volume. Photo and field plots, when combined in a stratified sampling design, proved about twice as efficient as simple field sampling. Although some gains were made by stratifying into only two classes–forest and nonforest–substantially greater gains accrued when the forest plots were further stratified into timber volume classes. Optimum allocation of field plots was only slightly more efficient than proportional allocation.