Estimating forest area at the year 1990 by two-phase sampling on historical remotely sensed imagery in Italy

Abstract

Forest area in the year 1990 is a fi gure of great interest under the Kyoto Protocol. This note is devoted to a scientifi c exercise for the probabilistic ex post assessment of such a fi gure in Italy. Estimation was performed by twophase point sampling, which made use of historical remotely sensed imagery. In the fi rst phase, a sample of 12 089 points was selected according to an unaligned systematic sampling and the selected points were classifi ed in land-use categories by Landsat 5 TM imagery. In the second phase, a sample of 3000 points was selected by stratifi ed sampling in which the strata were determined by the satellite classifi cation and the selected points were classifi ed by aerial photos, assumed as ground truth. A two-phase estimate of land-use coverage partitioning the Italian territory was obtained together with a conservative estimate of the sampling variance-covariance. The procedure has proved to be of relatively easy implementation and objective repeatability