Caveats include: Maps in this series are naturally correlated since all came from one map. No warranty or claim is made of the utility of this map for any particular purpose, this is considered to be a research dataset. The U-Index map portrays relative U, considering only agriculture and urban land uses as inferred from the descriptions of the MRLC cover types.
Land cover data (MRLC) was obtained from EROS Data Center in binary format.
The image was subdivided into sixteen (16) overlapping rectangles using an in-house software tool named SPLITTER.C. The rectangles overlapped to avoid artifacts near image boundaries during the spatial filtering operations.
Each of the rectangles was then processed via spatial filtering to estimate the index as described below. The spatial filtering program is an in-house software tool named SPATCONV.C (Riitters et al. 1996)
After spatial filtering, a map of index values was constructed by reassembling the 16 rectangles into a single image (via an in-house software tool named LUMPER.C, which removed the overlapping parts of rectangles).
The "header file" information for the derived map is as follows. This information is needed for some image import filters. Ulxmap and Ulymap refer to the center of the upper-left pixel. nrows 13240 ncols 13265 nbands 1 nbits 8 layout bsq skipbytes 0 ulxmap 1154670.000000 ulymap 2064600.000000 xdim 30.000000 ydim 30.000000
Spatial filtering proceeded as follows.
Pixels were re-classified into U (agriculture, urban) and "not U" (other classes) by using the following scheme:
Original MRLC class U or not class 11: open water missing 12: perennial ice/snow missing 21: low intensity developed U 22: high intensity residential U 23: high intensity commercial/industrial U 31: bare rock/sand/clay not U 32: quarries/strip mines/gravel pits U 33: transitional barren U 41: deciduous forest not U 42: evergreen forest not U 43: mixed forest not U 51: deciduous shrubland not U 52: evergreen shrubland not U 53: mixed shrubland not U 61: planted/cultivated (orchards, vineyards, groves) U 71: grassland/herbaceous not U 81: hay/pasture U 82: row crops U 83: small grains U 84: bare soil U 85: other grass (lawns, city parks, golf courses) U 91: woody wetland not U 92: emergent herbaceous wetland not U
A 65.61 ha (27x27 pixel) quadrat was centered on each pixel of the original land cover map. The numbers of "U" and "not U" pixels were tabulated for the non-missing pixels in the window. The index was then computed as the number of U pixels, divided by the sum of numbers of U and not-U pixels. This yields a value of 0 when no U pixels are present, and a value of 1 when all non-missing pixels in a window are U.
If the center pixel was "missing" in the land cover map, then the index was assigned a "missing" value. Note that the index is defined for all other land cover types.
The calculated values were discretized to the range [1,255] and stored at 30-meter spatial resolution. Thus, a pixel value in the new map represents the index for the surrounding 65.61 ha in the original land cover map.
The transformation used to discretize the values was: D = ( C * 254 ) + 1 where D = discretized value in range [1,255] C = calculated value in range [0,1] If needed, the original calculated values can be approximated by applying the backtransformation: C = ( D - 1 ) / 254 The backtransformed values will be in steps of size approximately 0.00394 as a result of the discretization process.