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Thematic Accuracy of the NLCD 2001 Land Cover for the Conterminous United States
Citation:
WICKHAM, J. D., S. V. Stehman, J. A. Fry, J. H. Smith, AND C. G. Homer. Thematic Accuracy of the NLCD 2001 Land Cover for the Conterminous United States. REMOTE SENSING OF ENVIRONMENT. Elsevier Science Ltd, New York, NY, 14(6):1286-1296, (2010).
Impact/Purpose:
The National Land Cover Database (NLCD), developed by the MultiResolution Land Characteristics (MRLC) Consortium (www.mrlc,gov) continues to be the primary source ofland- cover data in the United States. The paper announcing MRLC's inaugural land-cover map, NLCD 1992 (Vogelmann et aI., 2001), has been cited 320 times', reflecting the widespread need for the data. NLCD 1992 has been used to study habitat loss (Hoekstra et aI., 2005), conservation options (Carr et aI., 2002; Weber 2004; Weber et aI., 2006), the contribution ofland remote sensing to ecological study (Cohen & Goward, 2004), urban sprawl (Radeloff et aI., 2(05), forest fragmentation (Heilman et aI. 2002; Riitters et aI., 2002), nitrate contamination of groundwater (Nolan et aI., 2002), water quality (Doherty & Johnston, 2003), land use impacts on precipitation patterns (Marshall et aI., 2004) and net primary productivity (Milesi et aI., 2003), human exposure to disease vectors (Jackson et aI., 2006), model Total Maximum Daily Loads (TMDL) for the Clean Water Act (Wagner et aI., 2007), and many other applications (Stehman et aI., 2008).
Description:
The land-eover thematic accuracy ofNLCD 2001 was assessed from a probability-sample of 15,000 pixels. Nationwide, NLCD 2001 overall Anderson Level II and Level I accuracies were 78.7% and 85.3%, respectively. By comparison, overall accuracies at Level II and Level I for the NLCD 1992 were 58% and 80%. Forest and cropland were two classes showing substantial improvements in accuracy in NLCD 2001 relative to NLCD 1992. NLCD 2001 forest and cropland user's accuracies were 87% and 82%, respectively, compared to 80% and 43% for NLCD 1992. Accuracy results are reported for 10 geographic regions of the United States, with regional overall accuracies ranging from 68% to 86% for Level II and from 79% to 91% at Level I. Geographic variation in class-specific accuracy was strongly associated with the phenomenon that regionally more abundant land-cover classes had higher accuracy. Accuracy estimates based on several definitions of agreement are reported to provide an indication of the potential impact of reference data error on accuracy. Drawing on our experience from two NLCD national accuracy assessments, we discuss the use of designs incorporating auxiliary data to more seamlessly quantify reference data quality as a means to further advance thematic map accuracy assessment.