Simple instrument for measurement of remote sensing reflectance in coastal environment

Measurement of spectral remote sensing reflectance is essential to characterize water color, and to further estimate various water constituents with bio-optical algorithms. The measurement is critical to satellite data calibration/validation as well as to bio-optical algorithm development. Unfortunately, commercial instruments for such measurement are expensive, and they are either not capable of displaying data in real-time or not easy to use in coastal environment where large vessels are not applicable. In this paper we describe a simple instrument for such measurement. The fiber-optic Ocean Optics S2000 spectrometer, originally designed for lab use, was further developed to measure remote sensing reflectance. Compared with concurrent measurements from other expensive commercial instruments over different water bodies, the measured spectral reflectance is nearly identical (mean RMS difference < 2%). Through linearity and sensitivity analysis we found that it is capable of characterizing a variety of water types, even though the sensitivity is not as high as its commercial counterparts. The instrument substantially reduces the cost; it has real-time display and is easy to operate (< 0.5 kg) on small vessels. Further, combined with a liquid waveguide and a light source it is also capable of measuring Gelbstoff absorption with sufficient accuracy.