Removing glint effects from field radiometry data measured in optically complex coastal and inland waters

Abstract

Close range hyperspectral remote sensing is an important tool for cal/val of satellite and airborne remote sensing data. However, automated radiometer systems on jetties, ships of opportunity, and buoys as well as hand-held instruments are nowadays more frequently used as monitoring methods in their own right. One of the problems in interpreting the data collected during field measurements is removing sun and sky glint from the reflectance spectra. Current methods for removal of the surface effects have not been very successful. We developed a method where power functions are used to remove reflected component from measured reflectance spectra. Reflectance values in the 350–380nm range are used to determine the slope of the power function and reflectance values in the 890–900nm range are used to determine the absolute value of glint. We show that fitting a power function through these two spectral regions allows the removal of reflected light component from the measured reflectance spectra. Data from nearly 300 field sites in lakes and coastal waters as well as Hydrolight simulations were used to demonstrate the suitability of the method. The method performs well in optically deep and shallow waters as well as in variable illumination and wind conditions, does not require any auxiliary data besides the reflectance itself and is simple to apply even in the case of continuous data flow coming from field radiometers installed on buoys, research vessels or ships of opportunity.