The NLCD-MODIS land cover-albedo database integrates high-quality MODIS albedo observations with areas of homogeneous land cover from NLCD. The spatial resolution (pixel size) of the database is 480m-x-480m aligned to the standardized UGSG Albers Equal-Area projection. The spatial extent of the database is the continental United States.
The NLCD portion of the database includes all pixels (480m-x-480m) of homogeneous land cover for NLCD 2001, 2006, and 2011. Homogeneity was defined using tiles whose cells were 480m-x-480m and extracting those cells that had only a single land cover class at the native NLCD spatial resolution (30m-x-30m). Four additional layers are also included in the NLCD portion of the database: 1) a conflation of NLCD 2001, 2006, and 2011 homogeneous pixels, which can be used to identify land cover change; 2) elevation; 3) slope, and; 4) aspect. The conflated land cover layer identifies all pixels that were homogeneous across all three NLCD eras (2001, 2006, 2011). The conflated land cover layer does not include pixels that lost or gained homogeneity from one era to the next. Elevation, slope, and aspect were derived from the 30m-x-30m national elevation database (http://ned.usgs.gov), and like NLCD, were converted to a 480m-x-480m pixel. For elevation and slope, the 480m-x-480m pixel value is the mean of all 30m-x-30m pixel values, and for aspect, 480m-x-480m pixel value is the mode of all 30m-x-30m pixel values. Elevation is an integer raster in centimeters (cm). Slope is also an integer raster expressed as a percentage. Aspect is an integer raster based on a 5-class model (1=N, 2=E, 3=S, 4=W, 255=Flat). The topographic data are included for all pixels (480m-x-480m) in the continental U.S., not just for areas of homogeneous land cover.
The MODIS albedo observations include white-sky and black-sky albedos for the visible (0.3 - 0.7 µm), near-infrared (0.7 - 5.0 µm), and shortwave portions of the electromagnetic spectrum (0.3 - 5.0 µm) for 2000 through 2013 based on the MODIS MCD43A3 product. The temporal resolution of MODIS MCD43A3 product is eight (8) days, resulting in 46 albedo data layers per year. The MODIS albedo product includes data quality flags that can be used to distinguish observations that meet all a data quality objectives (i.e., high quality) from those that do not. A complete discussion of MODIS data quality is found in Schaaf et al. (2002). Only the high quality MODIS albedo observations were retained in the NLCD-MODIS land cover-albedo database.
The MODIS data quality information also includes attributes that identify the presence of snow. The NLCD-MODIS land cover-albedo database includes a binary layer for each date (i.e., 46 dates per year for each year) that identifies whether or not snow was present (1=snow). Like the albedo data layers, the binary snow layer only includes high quality observations. Both the albedo and binary snow data layers include all high quality observations, not only the high quality observations for which there is coincident homogeneous land cover. Users should note that albedo values are not distinguished as snow-covered or snow-free. The albedo data include all high quality observations, and the binary snow layer is used to determine whether or not an albedo for a given pixel was acquired in the presence of snow.
In part because observations are often "missing" due to the lack of high quality observations, the NLCD-MODIS land cover-albedo database also includes a data layer that tallies the number of high quality observations per pixel. The summation was done for each date and for the entire period of record (2000-2013) for both the albedo data layers and the binary snow layer.
The NLCD-MODIS land cover-albedo database is distributed in an ArcMap (version 10) geodatabase format that is organized into 16 sections (i.e., 16 different geodatabases). Fourteen (14) are MODIS albedo observations, one for each individual year. Within the albedo-by-year sections there are seven (7) data layers for each of the 46 observation dates per year (i.e., 6 data layers of albedo and an additional binary snow data layer). The albedo-by-year sections for 2001-2013 include all 46 dates, resulting in a total of 322 data layers. The albedo-by-year section for 2000 only includes 40 dates because January through mid-February observations are missing. The section for the number of high quality MODIS albedo observations includes 94 data layers. In this section there are two data layers for each of 46 dates, one for the high-quality albedo observations and one for the binary snow data layer. Two additional data layers in this section provide the number of high quality observations for the period of record (2000-2013), one for the high quality albedo observations and one for the binary snow data layer. The final section includes the NLCD land cover and related topographic data. The land cover section included NLCD for 2001, 2006, and 2011, the conflated NLCD land cover, and elevation, slope, and aspect. In total, there are 4,567 data layers in the NLCD-MODIS land cover-albedo database.
Preferred NLCD-MODIS Land Cover-Albedo Database citation: Wickham, J., Barnes, C.A., and Wade, T.G. 2015. Combining NLCD and MODIS to create a land cover-albedo database for the continental United States. Remote Sensing of Environment. 170, 143-152.