From one- to two-phase sampling to reduce costs of remote sensing-based estimation of land-cover and land-use proportions and their changes

- A two-phase strategy for land-cover, land-use estimation is proposed and tested.
- The one-per-stratum stratified sampling was used to select the second-phase points.
- The precision lost due to the two-phase sampling was evaluated.
- The new classification effort was 100 times smaller than the one-phase.
- The relative standard errors of the two-phase survey increased about 10 times.

The estimation of the proportion of land-cover and land-use classes is considered by exploiting remote sensing-based imagery. A pure-panel survey based on point sampling is adopted. An initial sample of points is selected by means of tessellation stratified sampling (TSS). The sample points are classified based on the imagery available for the years of interest to estimate land-cover or land-use proportions and their changes. To reduce the sampling effort, the initial selection of points is viewed as the first phase of sampling and a subsample of these points is selected in a second phase by means of one-per-stratum stratified sampling (OPSS). Land-use estimation at any subsequent year is then based on the classifications performed on the points of the second-phase sample. Two-phase estimators of proportions and of their changes are suggested, and their theoretical properties are derived. Presumably conservative estimators of their variances are proposed. A check of the precision lost involved when changing from one- to two-phase sampling is determined from the assessment of land use in Italy as a case study and from an artificial population generated to resemble the current land-use situation in Italy.