Effect of mineral dust on ocean color retrievals from space: A radiative transfer simulation study

Thursday, 18 December 2014
Ziauddin Ahmad1,2 and Bryan A Franz2, (1)JHT, Inc., Orlando, FL, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States
Mineral aerosols (dust) are one of the major components of all aerosols found in
the Earth’s atmosphere. They are mainly soil particles that originate from arid
and semiarid regions of the world that can be carried by winds for thousands of
kilometers. They are a major impediment in the remote sensing of the ocean
color (spectral water-leaving reflectance), because they absorb solar radiation
in the UV and visible part of the spectrum and their micro-physical and optical
properties are highly variable. Further, there are no reliable working
algorithms to detect their presence from spaceborne ocean color observations
alone, when they are present in small amount (optical thickness < 0.2).

In this paper we examine effect of mineral dust on ocean color retrieval from
space. We use Ahmad-Fraser’s vector radiative transfer (RT) code (v3.0) for
ocean-atmosphere system to simulate the pseudo observations (top of atmosphere
radiance) for models containing different types of aerosols (absorbing and
non-absorbing) in the atmosphere. We consider the mineral aerosols as consisting
of an external mixture of illite, kaolinite, montmorillonite, quartz, and
calcite with a small amount of hematite (as an internal mixture), which provide
the spectral dependence of single scattering albedo consistent with the values
reported in the literature. We also vary the aerosol layer height in the
atmosphere and amount of chlorophyll in the ocean. The simulated pseudo
observations were processed through standard NASA algorithms to determine the
ocean color (spectral water-leaving reflectance) and derived chlorophyll in the
ocean. Results of the RT simulation study for different Sun-satellite viewing
geometry, aerosol layer height and chlorophyll amount in the ocean is presented.