Abstract
Passive ocean color images have provided a sustained synoptic view of the distribution of ocean optical properties and color and biogeochemical parameters for the past 20-plus years. These images have revolutionized our view of the ocean. Remote sensing of ocean color has relied on measurements of the radiance emerging at the top of the atmosphere, thus neglecting the polarization and the vertical components. Ocean color remote sensing utilizes the intensity and spectral variation of visible light scattered upward from beneath the ocean surface to derive concentrations of biogeochemical constituents and inherent optical properties within the ocean surface layer. However, these measurements have some limitations. Specifically, the measured property is a weighted-integrated value over a relatively shallow depth, it provides no information during the night and retrievals are compromised by clouds, absorbing aerosols, and low Sun zenithal angles. In addition, ocean color data provide limited information on the morphology and size distribution of marine particles. Major advances in our understanding of global ocean ecosystems will require measurements from new technologies, specifically lidar and polarimetry. These new techniques have been widely used for atmospheric applications but have not had as much as interest from the ocean color community. This is due to many factors including limited access to in-situ instruments and/or space-borne sensors and lack of attention in university courses and ocean science summer schools curricula. However, lidar and polarimetry technology will complement standard ocean color products by providing depth-resolved values of attenuation and scattering parameters and additional information about particle morphology and chemical composition. This review aims at presenting the basics of these techniques, examples of applications and at advocating for the development of in-situ and space-borne sensors. Recommendations are provided on actions that would foster the embrace of lidar and polarimetry as powerful remote sensing tools by the ocean science community.
Highlights
Since the inception of ocean color satellite observation systems, remote sensing has been based on measurements of the radiance emerging at the top of the Ocean color remote sensing utilizes the intensity and spectral variation of visible light scattered upward from beneath the ocean surface to derive concentrations of biogeochemical constituents and inherent optical properties within the ocean surface layer
Passive radiometric space-borne observations of the ocean color allow for the estimation of the optical properties and concentration of the marine particles, weighted- over the first meters near the surface of the ocean
It is time to go beyond these observations to get access to (1) the profiles of these parameters through the first 3 optical depths and (2) information about the shape and concentration of these marine particles
Summary
Since the inception of ocean color satellite observation systems, remote sensing has been based on measurements of the radiance emerging at the top of the Ocean color remote sensing utilizes the intensity and spectral variation of visible light scattered upward from beneath the ocean surface to derive concentrations of biogeochemical constituents and inherent optical properties within the ocean surface layer. Using 473 and 532 nm microchip pulsed lasers, a lidar payload designed for small autonomous underwater vehicles (AUV) deployment uses narrow field-of view receiver channels at each wavelength to estimate range-resolved water column attenuation, and backscattering coefficients (Strait et al, 2018) These results suggest that a time/range-resolved differential absorption lidar (DIAL) approach can be used to resolve water column bio-optical components. Accurate retrieval of attenuation and particulate backscatter, another powerful feature of the HSRL technique is the ability to maintain calibration through the entire profile This is important for higher-altitude airborne (and future spaceborne) implementations for which the intervening atmosphere variably attenuates the received ocean signal due to variations in aerosol and/or cloud optical depth.
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