Inherent optical properties of the Irish Sea and their effect on satellite primary production algorithms

Abstract

Three cruises were conducted in the Irish Sea during May, June and July 2001 to determine the variability in inherent optical properties (IOP), photo physiological parameters and primary production (PP) and to assess the effect of IOP on satellite PP algorithms. The absorption coefficients of phytoplankton (aph), coloured dissolved organic material (aCDOM) and nonalgal particles (aNAP) were higher during May than June and July. A radiative transfer model was used to model the in-water light field based on aph (case 1) and aph, aCDOM and aNAP (case 2). When PP was compared using these light fields, there was a 46% difference in estimates. The case 2 in-water light field was coupled to a wavelength resolving satellite model of PP (PPcase2) and had a low root mean square error (RMS) (0.27 log10PP) compared with in situ PPcase2. IOP absorption, especially aCDOM, had a significant effect on the performance of this algorithm, but scattering of light by suspended particulate material had a small effect. A look-up table was generated from the in situ aph, aCDOM and aNAP measurements, which can be used in conjunction with satellite products to produce satellite maps of PP. There was <25% difference between in situ PPcase2 and the satellite PP maps, which suggests that they could be produced routinely and accurately to monitor PP in the Irish Sea and other coastal and estuarine areas.