Abstract.Airborne plumes of desert dust from North Africa are observable all year on satellite images over the Tropical Atlantic. In addition to its radiative impact, it has been suggested that this mineral dust has a substantial influence on the marine productivity. This effect is however difficult to gauge because present atmospheric correction algorithms for ocean color sensors are not capable of handling absorbing mineral dust. We apply a new approach to atmospheric correction in which the atmosphere is removed and the case I water properties are derived simultaneously. Analysis of SeaWiFS images acquired off Western Africa during a dust storm demonstrates the efficacy of this approach in terms of increased coverage and more reliable pigment retrievals.
When strongly absorbing aerosols are present in the atmosphere, the usual two-step procedure of processing ocean color data-(1) atmospheric correction to provide the water-leaving reflectance (rho(w)), followed by (2) relating rho(w) to the water constituents-fails and simultaneous estimation of the ocean and aerosol optical properties is necessary. We explore the efficacy of using a simple model of the aerosol-a Junge power-law size distribution consisting of homogeneous spheres with arbitrary refractive index-in a nonlinear optimization procedure for estimating the relevant oceanic and atmospheric parameters for case 1 waters. Using simulated test data generated from more realistic aerosol size distributions (sums of log-normally distributed components with different compositions), we show that the ocean's pigment concentration (C) can be retrieved with good accuracy in the presence of weakly or strongly absorbing aerosols. However, because of significant differences in the scattering phase functions for the test and power-law distributions, large error is possible in the estimate of the aerosol optical thickness. The positive result for C suggests that the detailed shape of the aerosol-scattering phase function is not relevant to the atmospheric correction of ocean color sensors. The relevant parameters are the aerosol single-scattering albedo and the spectral variation of the aerosol optical depth. We argue that the assumption of aerosol sphericity should not restrict the validity of the algorithm and suggest an avenue for including colored aerosols, e.g., wind-blown dust, in the procedure. A significant advantage of the new approach is that realistic multicomponent aerosol models are not required for the retrieval of C.
The purpose of this paper is to explore three-dimensional magnetic recording as a next generation recording technology. To defer the superparamagnetic limit in magnetic recording substantially beyond the 1Tbit∕in.2 mark, it is proposed to stack magnetic bits in a third (vertical) dimension. The vertical stacking underlies the concept of three-dimensional (3D) magnetic memory and recording—the primary subject of this paper. A clear distinction between absolute 3D memory and its trivial multilevel implementation is drawn. The paper focuses on the study of the media design and write and read processes. To minimize the intersymbol interference and improve stability, it is proposed to pattern the recording media in all three dimensions. Basic Co∕Pd-based 3D recording media necessary for this study are fabricated using cosputter deposition. Focused-ion-beam-based fabrication is used to pattern the recording media into nanoscale bit cells. The physics of 3D magnetic recording is also investigated theoretically with Landau-Lifshits-Gilbert-based micromagnetic modeling. The ultimate goal of this paper is to help understand the physics of 3D and multilevel magnetic recordings and trigger wide interest in the studied concept.
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