The MODIS sensors aboard the twin satellites Aqua and Terra provide global coverage of earth’s surface every 1 to 2 days. MODIS’s spatial, spectral, and temporal resolution allow for imagery to be utilized for regional monitoring of vegetation, land surface temperature, and the environment. MODIS data is available for Terra (daily, 8 day, or 16 day composites), Aqua (daily, 8 day, or 16 day composites), and composite of Terra/Aqua 16 day using at surface reflectance data.
Normalized Difference Water Index (NDWI) (Green/SWIR2) is a water index which provides information on open water extent. This product typically ranges from -1 to 0.25 where water is typically above 0.04 (Özelkan 2020). This product is useful for identifying open water to use in estimating water surface area or removal through masking.
NDWI (Green/SWIR2) is the normalized difference between the green and short wave near infrared 1 (SWIR2) bands following the equation (Green-SWIR2)/(Green+SWIR2). Water reflects Green and absorbs SWIR2 electromagnetic radiation while vegetation and soil absorbs Green and reflects SWIR2 electromagnetic radiation (Xu 2006). The result is a high normalized difference (ND) over water and a low ND over land with high contrast.
Short Wave Infrared 2 (SWIR2): 2.105-2.155 μm
Green: 0.545-0.565 μm
Period of Record
Xu, H. (2006). Modification of normalised difference water index (NDWI) to enhance open water features in remotely sensed imagery. International journal of remote sensing, 27(14), 3025-3033.
Özelkan, E. (2020). Water body detection analysis using NDWI indices derived from Landsat-8 OLI. Polish Journal of Environmental Studies, 29(2), 1759-1769.
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