Relationship between the irradiance reflectance and inherent optical properties of seawater

Hirata, Takafumi; Højerslev, Niels K.

doi:10.1029/2007jc004325

Cited by 10 publications

(6 citation statements)

References 29 publications

(46 reference statements)

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“…In the Santa Barbara Channel, the downwelling and upwelling radiance distribution were measured separately in time, so did not give an accurate estimate for d . We started the inversion with the following expression [ Hirata and Højerslev , 2008], K d ( z ) d ≈ a ( z ) + b b ( z ), where b b represents the backscattering coefficient and this expression holds for surface waters where E od ≫ E ou holds. Figure 8b shows the results for ( a + b b ) in the Channel.…”

Section: Resultsmentioning

confidence: 99%

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Quantitative estimation of the underwater radiance distribution

Lewis

Wei

Dommelen³

et al. 2011

J. Geophys. Res.

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[1] Within the Radiance in a Dynamic Ocean (RaDyO) program, we have created and deployed a high dynamic range camera that can resolve the full spherical radiance distribution at the ocean surface and at depth. We present here the first results from deployments of the camera in near-surface water in eutrophic, mesotropic, and oligotropic environments. The instrument resolves the dynamics and fine structure of both the downwelling and upwelling radiance distribution and its variation with depth in these optically diverse water types. The various irradiances (E d , E u , E o , E ou , and E od ) are computed by integration. The distribution functions (e.g., the average cosines) are computed directly, as are the various diffuse attenuation coefficients. The fully specified radiance field therefore provides all the pertinent information to derive not only all of the apparent optical properties but, in principle, the inherent optical properties such as the absorption coefficient and the phase function as well. Comparison of the measured radiance field to independent measurements has shown very good agreement.

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Section: Resultsmentioning

confidence: 99%

Section: Inherent Optical Propertiesmentioning

confidence: 99%

Quantitative estimation of the underwater radiance distribution

Lewis

Wei

Dommelen³

et al. 2011

J. Geophys. Res.

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“…We calculated Z SD according to the equation of Preisendorfer [1986] with Γ calculated by with the beam attenuation coefficient c (= a + b ) and K d evaluated at 555 nm, close to the most penetrating wavelength in middle and lower Chesapeake Bay, and at the maximum sensitivity of the light‐adapted human eye [ Davies‐Colley et al , 2003]. We assumed a contrast threshold, C t = 0.066, disk reflectivity, R disk = 0.82 [ Davies‐Colley and Vant , 1988], and calculated in situ reflectance by with f ′ evaluated according to Morel and Gentili [1993] as cited by Hirata and Højerslev [2008].…”

Section: Bio‐optical Modelmentioning

confidence: 99%

Long‐term changes in light scattering in Chesapeake Bay inferred from Secchi depth, light attenuation, and remote sensing measurements

2011

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[1] The relationship between the Secchi depth (Z SD ) and the diffuse attenuation coefficient for photosynthetically active radiation (K d (PAR)), and in particular the product of the two, Z SD · K d (PAR), is governed primarily by the ratio of light scattering to absorption. We analyzed measurements of Z SD and K d (PAR) at main stem stations in Chesapeake Bay and found that the Z SD · K d (PAR) product has declined at rates varying from 0.020 to 0.033 yr −1 over the 17 to 25 years of measurement, implying that there has been a long-term increase in the scattering-to-absorption ratio. Remote sensing reflectance at the green wavelength most relevant to Z SD and K d (PAR) in these waters, R rs (555), did not exhibit an increasing trend over the 10 years of available measurements. To reconcile the observations we constructed a bio-optical model to calculate, and R rs (555) as a function of light attenuating substances and their mass-specific absorption and scattering coefficients. When simulations were based exclusively on changes in concentrations of light attenuating substances, a declining trend in Z SD · K d entailed an increasing trend in R rs (555), contrary to observations. To simulate both decreasing Z SD · K d (PAR) and stationary R rs (555), it was necessary to allow for a declining trend in the ratio of backscattering to total scattering. Within our simulations, this was accomplished by increasing the relative proportion of organic detritus with high mass-specific scattering and low backscattering ratio. An alternative explanation not explicitly modeled is an increasing tendency for the particulate matter to occur in large aggregates. Data to discriminate between these alternatives are not available.

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“…where f indicates the relationship between irradiance reflectance and IOPs ( [74] and references therein) and Q (ratio of upwelling radiance to irradiance) [75] represents the directional nature of upwelling light field. The term f/Q is equivalent to G0(uT) + G1(uT), and r rs (0−) could be rewritten as below:…”

Section: Relationship Between Underwater Remote Sensing Reflectance Amentioning

confidence: 99%

A Semi-Analytical Optical Remote Sensing Model to Estimate Suspended Sediment and Dissolved Organic Carbon in Tropical Coastal Waters Influenced by Peatland-Draining River Discharges off Sarawak, Borneo

et al. 2020

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Coastal water quality degradation is a global challenge. Marine pollution due to suspended sediments and dissolved matter impacts water colour, biogeochemistry, benthic habitats and eventually human populations that depend on marine resources. In Sarawak (Malaysian Borneo), peatland-draining river discharges containing suspended sediments and dissolved organic carbon influence coastal water quality at multiple locations along the coast. Optical remote sensing is an effective tool to monitor coastal waters over large areas and across remote geographic locations. However, the lack of regional optical measurements and inversion models limits the use of remote sensing observations for water quality monitoring in Sarawak. To overcome this limitation, we have (1) compiled a regional spectral optical library for Sarawak coastal waters, (2) developed a new semi-analytical remote sensing model to estimate suspended sediment and dissolved organic carbon in coastal waters, and (3) demonstrated the application of our remote sensing inversion model on satellite data over Sarawak. Bio-optical data analysis revealed that there is a clear spatial variability in the inherent optical properties of particulate and dissolved matter in Sarawak. Our optical inversion model coupled with the Sarawak spectral optical library performed well in retrieving suspended sediment (bias = 3% and MAE = 5%) and dissolved organic carbon (bias = 3% and MAE = 8%) concentrations. Demonstration products using MODIS Aqua data clearly showed the influence of large rivers such as the Rajang and Lupar in discharging suspended sediments and dissolved organic carbon into coastal waters. The bio-optical parameterisation, optical model, and remote sensing inversion approach detailed here can now help improve monitoring and management of coastal water quality in Sarawak.

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Relationship between the irradiance reflectance and inherent optical properties of seawater

Cited by 10 publications

References 29 publications

Quantitative estimation of the underwater radiance distribution

Quantitative estimation of the underwater radiance distribution

Long‐term changes in light scattering in Chesapeake Bay inferred from Secchi depth, light attenuation, and remote sensing measurements

A Semi-Analytical Optical Remote Sensing Model to Estimate Suspended Sediment and Dissolved Organic Carbon in Tropical Coastal Waters Influenced by Peatland-Draining River Discharges off Sarawak, Borneo

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