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Forecast Mekong

Normalized Difference Water Index (NDWI)

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Monthly Normalized Difference Water Index (NDWI) products are available for 2003-2011. These products are derived from MOD09 reflectance data that has been atmospherically corrected, cloud-masked, and temporally processed with the Time Series Product Tool (TSPT) to further mitigate noise and interpolate data voids. The NDWI products shown here are derived using the NDWI formula originally published by McFeeters (1996). The McFeeters’ NDWI is computed as follows: [NDWI = (Xgreen – Xnir)/(Xgreen + Xnir)], where Xgreen refers to the green band (MODIS band 4) and Xnir refers to the nir band (MODIS band 2). This formulation of NDWI produces an image in which the positive data values are typically open water areas; while the negative values are typically non-water features (i.e. terrestrial vegetation and bare soil dominated cover types). Like NDVI, NDWI has a native scaling of -1 to +1. The NDWI products were processed at a spatial resolution of about 463 meters per pixel. These products offer a means to view water bodies and may be useful for assessing flooding impacts. This NDWI was utilized over other available forms in part because the output appears to be cleaner with less apparent noise. The NDWI products can be used in conjunction with NDVI change products to assess context of apparent change areas.

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Page Last Modified: Friday, April 07, 2017