Marine Particulate Absorption Techniques and Applications in the Study of Inherent and Apparent Optical Properties of the Ocean

Abstract

Overview of ONR sponsored research to Dr. B. Greg Mitchell, and long-range goals A thorough understanding of marine optics is a mission of significant Naval relevance. The ability to use optical measurements (in situ and remote)_to estimate light propagation and phytoplankton growth rates is a significant objective. This objective requires a detailed understanding of the nature and variability of source and loss terms, and an ability to model the relevant rates. Figure 1 summarizes dominant state variables and transformations occurring in marine optics, and the contributions by the principal investigator in understanding these processes. Several significant problems previously have not been resolved with respect to measuring or modeling the processes in Figure 1. The long-range objectives of the principal investigator is to continue studies of the various components and rate processes shown in Figure I in an effort to improve our understanding of marine optical properties and photo-physiology and ecology of phytoplankton. Figure 1. A conceptual model of optically important processes in the ocean. The long-range objectives of our research include a detailed understanding of the processes and state variables specified in this figure. The state variables in the boxes (S1-S6) correspond to dominant sources of optical variability in the oceans. The principal investigator has dedicated his research effort to understanding the diverse aspects of this system. Methods for estimating the magnitude and characteristics of Si, S2 and 53 have included analysis of particle absorption using microphotometry (Iturriaga et al, 1988); macrophotometry (Mitchell and Kiefer, 1984;Mitchell et al. 1984;Mitchell and Kiefer, 1988a;1988b; Mitchell, 1990); in situ optical profiling resulting in discovery of regional bio-optical relationships (Mitchell and HolmHansen, 1991a; Mitchell, 1992); a novel method to estimate S1 from moored radiometers (Stramski et al. 1992); and aircraft (Tanis et al., 1990) or satellite observations of biomass . Optical based models of phyoplankton photosynthesis for laboratory cultures (Kiefer and Mitchell, 1983; Sosik and Mitchell, 1991) for Antarctic phytoplankton (Mitchell and Hom-Hansen, 1991b) and for Arctic phytopplankton (Cota et al., 1992) have been developed to model process K1. Siegel et al. (1989) used an in situ optical approach to estimate K1 and K2+K5 for populations in the North Pacific Gyre. Carder et al. (1991) have used optical methods to partition S1 from S2 and S3 for remote sensing. Sedimentation rates of Antarctic and Arctic phytoplankton (K2) have been studied by Mitchell and Holm-Hansen (1991b) and Wassman et al., (1990). OBJECTIVS FOR GRANT N00014-J-90-1052The objectives of the work sponsored under ONR grant N00014-90-J-1052 was to apply the absorption methods developed during FY89 under grant N00014-89-J-1071. In FY89, the methodology of the Quantitative Filter Technique (OFT) Was verified and published. In FY90, the objectives were to utilize the methods in the study of specific ...