How is classification accuracy assessed?
The NLCD are assessed for accuracy based upon the Federal Regions (i.e. the reported accuracy is for the Region as a whole, rather than for individual states). Accuracy assessments follow a revision cycle that incorporates feedback from MRLC Consortium partners and affiliated users. Private sector vendors under contract to the USEPA conduct the accuracy assessments. A protocol has been established by the USGS and USEPA that incorporates a two-stage, geographically stratified cluster sampling plan (Zhu et al., 1999) utilizing National Aerial Photography Program (NAPP) photographs as the sampling frame and the basic sampling unit. In this design a NAPP photograph is defined as a 1st stage or primary sampling unit (PSU), and a sampled pixel within each PSU is treated as a 2nd stage or secondary sampling unit (SSU). PSU’s are selected from a sampling grid based on NAPP flight-lines and photo centers, each grid cell measures 15′ X 15′ (minutes of latitude/longitude) and consists of 32 NHAP
