NASA MODIS Turbidity
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Ocean turbidity (Turb) is derived from MODIS nLw products, which can be downloaded from NASA websites for free. Turb is defined as:
Turb(NTU) = 56.609(nLw_667nm/nLw_488nm)^2.2985
All products are geo-referenced to a cylindrical equidistance projection.
The standard MODIS nLw uses ratio value, which could reduce the signal distortion in high turbidity areas resulted from atmospheric correction.
This algorithm is based on voyage measurements in Mar. 2003~April 2003 and Oct. 2005~Mar.2006 . YSI6600 surface turbidity (0-1.5m) and ratio values between nLw_670nm and nLw_490nm measured by profile radiometer are employed in the derivation.
Users have to take regional difference into consideration while using of Turb products since optical properties might vary in different water areas.