Simultaneous determination of aerosol optical thickness and exponent of Junge power law from satellite measurements of two near-infrared bands over the ocean

Abstract. Retrieval of aerosol optical properties and water leaving radiance over ocean is changeling since the latter mostly accounts for ~10% of satellite observed signal and can be easily contaminated by the atmospheric scattering. Such an effort would be more difficulty in turbid coastal waters due to the existence of optically complex oceanic substances or high aerosol loading. In an effort to solve such problems, we present an optimization approach for the simultaneous determination of aerosol optical thickness (AOT) and normalized water leaving radiance (nLw) from multi-spectral measurements. In this algorithm, a coupled atmosphere-ocean radiative transfer model combined with a comprehensive bio-optical oceanic module is used to jointly simulate the satellite observed reflectance at the top of atmosphere and water leaving radiance just above the ocean surface. Then a full-physical nonlinear optimization method is adopted to retrieve AOT and nLw in one step. The algorithm is validated using Aerosol Robotic Network Ocean Color (AERONET-OC) products selected from eight OC sites distributed over different waters, consisting of observation cases covered both in and out of sun glint from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. Results show a good consistency between retrieved and in situ measurements in each site. It is demonstrated that more accurate AOT are determined based on the simultaneous retrieval method, particularly in shorter wavelengths and sun glint conditions, where the averaged percentage difference (APD) of retrieved AOT generally reduce by approximate 10 % in visible bands compared with those derived from the standard atmospheric correction (AC) scheme. It is caused that all the spectral measurements can be used jointly to increase the information content in the inversion of AOT and the wind speed is also simultaneously retrieved to compensate the specular reflectance error estimated from the rough ocean surface model. For the retrieval of nLw, over atmospheric correction can be avoided to have a significant improvement for the inversion of nLw at 412 nm. Furthermore, generally better estimates of band ratios of nLw(443)/nLw(554) and nLw(488)/nLw(554), which are employed in the inversion of chlorophyll a concentration (Chl), are obtained using simultaneous retrieval approach with less root mean square errors and relative differences than those derived from the standard AC approach in comparison to the AERONET-OC products, as a result that the APD value of retrieved Chl decreases by about 5 %. On the other hand, the standard AC scheme yields a more accurate retrieval of nLw at 488 nm, prompting a further optimization of oceanic bio-optical module of current model.

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Simultaneous determination of aerosol optical thickness and water-leaving radiance based on wavelength relationship among the water-leaving radiance

10.1117/12.619671 ◽

2005 ◽

Author(s):

Qingshan Xu ◽

Huanling Hu

Keyword(s):

Simultaneous Determination ◽

Optical Thickness ◽

Aerosol Optical Thickness

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Simultaneous determination of water-leaving reflectance and aerosol optical thickness from Coastal Zone Color Scanner measurements

Applied Optics ◽

10.1364/ao.36.006949 ◽

1997 ◽

Vol 36 (27) ◽

pp. 6949 ◽

Cited By ~ 17

Author(s):

Fengsheng Zhao ◽

Teruyuki Nakajima

Keyword(s):

Simultaneous Determination ◽

Coastal Zone ◽

Optical Thickness ◽

Aerosol Optical Thickness ◽

Color Scanner

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Remote sensing of aerosol properties from multi-wavelength and multi-pixel information over the ocean

10.5194/acp-2018-999 ◽

2018 ◽

Author(s):

Chong Shi ◽

Makiko Hashimoto ◽

Teruyuki Nakajima

Keyword(s):

Remote Sensing ◽

Spatial Variation ◽

Optical Thickness ◽

Measurement Errors ◽

Near Infrared ◽

Aerosol Optical Thickness ◽

Dust Particles ◽

Radiative Transfer Model ◽

Transfer Model ◽

Satellite Measurements

Abstract. In this study, we investigate the feasibility of multi-pixel scheme in the inversion of aerosol optical thickness (AOT) for multi-spectral satellite instruments over the ocean. Different from the traditional satellite aerosol retrievals conducted pixel by pixel independently, we derive the aerosol optical thickness of multiple pixels simultaneously by adding smoothness constraint on the spatial variation of aerosols and oceanic substances, which helps the satellite retrieval with higher consistency from pixel to pixel. Simulations are performed for two representative oceanic circumstances – open and coastal waters, as well as the land-ocean interface region. We retrieve the AOT for fine, sea spray, and dust particles simultaneously using synthetic spectral measurements from the Greenhouse Gases Observing Satellite/Thermal and Near Infrared Sensor for Carbon Observations-Cloud and Aerosol Imager (GOSAT/TANSO-CAI) with four wavelengths coving from the ultraviolet to shortwave infrared bands. The forward radiation calculation is performed by a coupled atmosphere-ocean radiative transfer model combined with a three-component bio-optical oceanic module, where the chlorophyll a concentration, sediment and colored dissolved organic matter are considered. Results show that accuracies of the derived AOT and spectral remote-sensing reflectance are both improved by applying smoothness constraints on the spatial variation of aerosol and oceanic substances in homogeneous or inhomogeneous surface conditions. The multi-pixel scheme can be effective to compensate the retrieval biases induced by measurement errors and improve the retrieval sensitivity, particularly for the fine aerosol over the coastal water. We then apply the algorithm to derive AOTs using real satellite measurements. Results indicate that the multi-pixel method helps to polish the irregular retrieved results of the satellite imagery and shows promising potentiality to correct the overestimation of aerosols over high turbid waters, by benefiting from the coincident retrieval of neighboring pixels. A comparison of retrieved AOTs from satellite measurements with those from the Aerosol Robotic Network (AERONET) also indicates that retrievals conducted by the multi-pixel scheme are more consistent with the AERONET observations.

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Simultaneous determination of aerosol optical thickness and water-leaving radiance from multispectral measurements in coastal waters

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-3865-2018 ◽

2018 ◽

Vol 18 (6) ◽

pp. 3865-3884 ◽

Cited By ~ 1

Author(s):

Chong Shi ◽

Teruyuki Nakajima

Keyword(s):

Simultaneous Determination ◽

Optical Thickness ◽

Coastal Waters ◽

Ocean Surface ◽

Aerosol Optical Thickness ◽

Surface Model ◽

Atmospheric Scattering ◽

Optical Module ◽

Mean Square Errors

Abstract. Retrieval of aerosol optical properties and water-leaving radiance over ocean is challenging since the latter mostly accounts for ∼  10 % of the satellite-observed signal and can be easily influenced by the atmospheric scattering. Such an effort would be more difficult in turbid coastal waters due to the existence of optically complex oceanic substances or high aerosol loading. In an effort to solve such problems, we present an optimization approach for the simultaneous determination of aerosol optical thickness (AOT) and normalized water-leaving radiance (nLw) from multispectral satellite measurements. In this algorithm, a coupled atmosphere–ocean radiative transfer model combined with a comprehensive bio-optical oceanic module is used to jointly simulate the satellite-observed reflectance at the top of atmosphere and water-leaving radiance just above the ocean surface. Then, an optimal estimation method is adopted to retrieve AOT and nLw iteratively. The algorithm is validated using Aerosol Robotic Network – Ocean Color (AERONET-OC) products selected from eight OC sites distributed over different waters, consisting of observations that covered glint and non-glint conditions from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. Results show a good consistency between retrieved and in situ measurements at each site. It is demonstrated that more accurate AOTs are determined based on the simultaneous retrieval method, particularly in shorter wavelengths and sunglint conditions, where the averaged percentage difference (APD) of retrieved AOT is generally reduced by approximate 10 % in visible bands compared with those derived from the standard atmospheric correction (AC) scheme, since all the spectral measurements can be used jointly to increase the information content in the inversion of AOT, and the wind speed is also simultaneously retrieved to compensate the specular reflectance error estimated from the rough ocean surface model. For the retrieval of nLw, atmospheric overcorrection can be avoided in order to have a significant improvement of the inversion of nLw at 412 nm. Furthermore, generally better estimates of band ratios of nLw(443) / nLw(554) and nLw(488) / nLw(554) are obtained using the simultaneous retrieval approach with lower root mean square errors and relative differences than those derived from the standard AC approach in comparison to the AERONET-OC products, as well as the APD values of retrieved Chl which decreased by about 5 %. On the other hand, the standard AC scheme yields a more accurate retrieval of nLw at 488 nm, prompting a further optimization of the oceanic bio-optical module of the current model.

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