A method to retrieve concentrations of suspended large and small particles in seawater from satellite images is proposed.
The method uses as input images of scattering and backscattering coefficients in several satellite channels as well as an
image of concentration of chlorophyll. All these three properties are derived using an atmospheric correction algorithm
and algorithms to derive inherent optical properties from remote sensing reflectance. The proposed method is based on
several approaches developed previously by Twardowski et al, van de Huist, and Evans and Fournier and is based on
Mie theory. The proposed method was applied to restore a number of suspended particles and their dynamics in ocean
using SeaWIFs satellite optical images.
The spatial and angular structure of light radiance in the depth of seawater can be precisely computed with such numerical programs like Hydrolight. Unfortunately such calculations demand a lot of computational time if used for problems of visibility of submerged objects. In this case, due to the much greater computational efficiency and logarithmic dependence of visibility parameters on radiance values, analytical radiative transfer methods are preferable. In this presentation a new analytical radiative transfer method is proposed to solve visibility problems in seawater. The
angular structure of depth-dependent light radiance in the sea is obtained in the framework of previously published selfconsistent
approximation. The analytical expressions proposed in this paper allow to compute a horizontal visibility of submerged objects. This approach can be applied to problems of diver visibility in shallow water bodies of arbitrary turbidity and illumination.
The remote sensing coefficient or radiance reflection coefficient is a principal product of atmospheric correction algorithms applied to the remotely measured optical images of the ocean. This coefficient contains information about angular structure of light radiance, roughness of the ocean surface, and optical properties of the water. This presentation analyses remote sensing coefficient and presents it as a product of three physically different values or factors. The first factor depends on geometrical parameters of illumination and atmospheric optical properties, the second factor depends on roughness of the ocean surface, and the third one depends on the optical properties of seawater. The approach used to derive the third in-water factor is valid for all levels of water turbidity - from the clearest open waters to the most turbid waters of river mouths and extremely scattering waters of Yellow Sea type.
This paper proposes a number of analytical approximations to the classic and recently measured seawater light scattering phase functions. The three types of analytical phase functions are derived: individual representations for 15 Petzold, 41 Mankovsky, and 91 Gulf of Mexico phase functions; collective fits to Petzold phase functions;
and analytical representations that take into account dependencies between inherent optical properties of seawater. The proposed phase functions may be used for problems of radiative transfer, remote sensing, visibility and image propagation in natural waters of various turbidity.
A new set of two optical spectral probes developed to measue content of organic and inorganic constituencies suspended and dissolved in natural water is proposed. The set is capable to measure spectral attenuation and absorption coefficients of light, total amounts of organic and terrigenic hydrosoles suspended in water, and amount of organic matter dissolved in natural water. It can be used to monitor water quality and measure optically active ingredients in oceans, lakes and other natural water basins.
This paper presents result of in-situ measurements of optical hyperspectral parameters, chlorophyll concentration and inherent and apparent optical properties of seawater. As a characteristic of hyperspectral optical measurements a CIE dominant wavelength and different color indices are used. Such important optical parameters as downward diffuse attenuation coefficient, diffuse reflection coefficient, beam attenuation coefficient, and seawater euphoric depth are measured and analyzed. Multiple regression relationships that connect hyperspectral data with biological and optical properties are proposed.
This paper presents experimentally obtained relationships between effective wavelength and a number of important seawater parameters such as dominant wavelength, different color indices, downward diffuse attenuation coefficient, absorption coefficient, seawater effective optical thickness, and a chlorophyll content. A number of regression relationships that connect hyperspectral measurements with listed bio-optical properties are prosed and discussed.
This paper present a statistical analysis of aerosol phase functions measured under marine conditions with the total atmospheric optical thickness. The result of the analysis is an empirical equation that expresses the aerosol phase function of scattering in the visible region through two tabulated empirical functions and a total aerosol optical thickness at 745 nm. The extrapolation of the atmospheric optical thickness to the visible spectrum is accomplished via an angstrom-type empirical equation that includes the wavelength of light and the aerosol optical thickness at 745 nm.
The algorithm presented in this paper is based on the previously published analytic theory by the author. That theory is based on the scalar radiative transfer approach and it generalizes the satellite Tanre-Deschampes algorithm to the aircraft situation. the restoration of the atmospheric optical parameters is based on a new empirical relationship between the scattering phase function by aerosols and the total aerosol optical thickness in the near IR. Examples of processed with the proposed algorithm airborne AVIRIS images of the Gulf of Mexico and North-West Atlantic in different spectral bands are presented.
The proposed approach is based on the theory developed for the marine environment. This approach is tuned to be valid in the whole range of optical properties including an unrealistic case of a totally scattering sea. Because the atmosphere below the ozone layer is totally scattering in the visible range of spectrum, the proposed approach may be applied to the atmosphere are presented. The proposed model allows to calculate spectral albedo of the ocean-atmosphere system as a function of three input parameters: the chlorophyll concentration, the aerosol atmospheric optical thickness at near IR, and the solar zenith angle.
The influence of the illumination by the direct sun light and the diffuse light of the sky on the spectral structure of the apparent optical properties of seawater is studied. The resulting formula of this paper couples the sea diffuse reflection coefficient with the angular distribution of the natural light and the inherent optical properties of the seawater. This work uses a self-consistent approach to solve the radiative transfer equation. That approach was developed earlier to calculate the apparent optical properties including the diffuse reflection coefficient. A model of the inherent optical properties of seawater is proposed. This model expresses the inherent optical properties through the concentrations of chlorophyll, yellow substance, and biogenic and terrigenic hydrosols. The transformations of sea optical signatures, due to the changes in illumination and concentrations of suspended and dissolved matter, are analyzed. It is shown that the atmospheric optical parameters and the sun elevation angle significantly influence optical signatures of the upwelling light. The effective wavelength -- the parameter that is weakly dependent on the conditions of illumination -- is proposed.
The spectral values of remotely obtained radiance reflectance coefficient (RRC) are compared with the values of RRC computed from inherent optical properties measured during the shipborne experiment near the West Florida coast. The model calculations are based on the algorithm developed at the Naval Research Laboratory at Stennis Space Center and presented here. The algorithm is based on the radiation transfer theory and uses regression relationships derived from experimental data. Overall comparison of derived and measured RRCs shows that this algorithm is suitable for processing ground truth data for the purposes of remote data calibration. The second part of this work consists of the evaluation of the predictive visibility model (PVM). The simulated three-dimensional values of optical properties are compared with the measured ones. Preliminary results of comparison are encouraging and show that the PVM can qualitatively predict the evolution of inherent optical properties in littoral waters.
Differential equations for the transmittance and the diffuse reflection coefficients of the stratified sea are obtained. To simplify starting radiative transfer equation, the approach uses experimental dependencies between mean cosines of underwater angular radiance distribution. The resulting equation for the diffuse reflectance coefficient is of a Riccati type. For the homogenous sea with arbitrary combination of inherent optical properties, that equation is solved analytically. For vertically inhomogeneous sea it is solved approximately. The resulting formula expresses diffuse reflection coefficient through the profiles of inherent optical properties of seawater and bottom depth and albedo. The results of calculations with main formula are compared with the Mont Carlo computations. It was found that the precision of this theory is about 15% and it is comparable with the precision of contemporary in situ measurements.
The results of model calculations of apparent optical properties of realistic marine waters with inclusion of Raman scattering and fluorescence are presented. It is shown that the underwater light spectrum can be divided, by a threshold wavelength, into two regions with different behavior of apparent optical properties, and also that inelastic effects are significant and should be considered in ocean optics measurements.
In studying light and image transfer in coastal waters the influence of bottom reflection is as significant as scattering and absorption phenomena. In these cases a knowledge of the reflective properties of different types of bottoms is very important. At present, little is known about these properties. We present results of experimental spectral measurements of different kinds of sedimental material such as sands and clays, both major components of coastal water bottoms. We have determined the spectral index of refraction from measurements of the optical spectral signatures of various clays and sands, as the represent the most common bottom components found in coastal waters. The measured optical spectral signatures and the associated complex indexes of refraction are presented. This preliminary study should provide insight on improving the inverse problem algorithm for extracting the spectral index of refraction. This spectral information can then be used as input into radiative transfer models which include the ocean bottom.
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