Imprints of atmospheric waves on the Black Sea surface in data of ocean color scanners

Data from MERIS onboard Envisat and MODIS onboard Terra and Aqua for 15–16 May 2010 were used to study powerful imprints of atmospheric gravity waves (AGWs) on the western part the Black Sea surface. Two cold fronts crossed the sea following the warm front and caused the AGWs which modulated the sea surface. Imprints of AGWs appeared as stripes of alternating brightness, they had crest length more than a hundred kilometers and wavelength of units of kilometers. Wave amplitude of AGWs imprints, evaluated by a 90%-depth of light penetration into the sea at 490 nm z90, the value inverse to the diffuse attenuation coefficient Kd_490, was units of decimeterxs. MODIS 250-m data of remote sensing reflectance, wind components and atmospheric pressure near the sea surface were obtained by processing the top of atmosphere data with the SeaDAS software package. Negative correlations of fluctuations of z90 with fluctuations of wind stress and atmospheric pressure were found on the transects of more than ten kilometers. The impact of wind stress on the origination of AGW imprints was found to be determinant, while the impact of atmospheric pressure was not more than units of percent

Narrowband shortwave minima in spectra of backscattered light from the sea obtained from ocean color scanners as a remote indication of algal blooms

SummaryWe propose a new approach to indication of algal blooms. It stems from analysis of the multispectral satellite reflectance Rrs of areas where blooms were documented during recent decades. We found that spectra of algal blooms exhibit minima at wavelengths of channels of Moderate Resolution Imaging Spectroradiometer (MODIS) λ=443 and λ=488nm (Baltic, Black, and Caspian seas), λ=443nm (Southwest Tropical Pacific (SWTP)), and λ=443nm and λ=469nm (Patagonian Continental Shelf (PCS)), attributable to absorption bands of chlorophyll a and accessory pigments. We quantified the minima using indices D1=Rrs(443)−Rrs(412) and D2=Rrs(488)−Rrs(469) and proved their diagnostic potential by comparing their distributions to that of Rrs(555). Linear dependence of D1 upon chlorophyll a was found from MODIS data for the bloom of Nodularia spumigena. Time dependences of D1 and D2 point to the latter as a probable remote forerunner of cyanobacterial blooms. In the PCS, D1 and D2 proved to be too simplistic owing to diversity of spectral shapes at λ<550nm. Cluster analysis revealed close linkage of the latter and local oceanological conditions. Our findings bear witness to the diagnostic potential of the indices by virtue of their direct relation to pigment absorption and because the broadband background reflectance changes reduce when calculating the indices as a difference of spectrally close reflectances. Further studies are needed to convert the indices to band-difference algorithms for retrieving the bio-optical characteristics of algal blooms

Influence of the wind field on the radiance of a marine shallow: evidence from the Caspian Sea

The influence of the near-water wind field on the radiance of a marine shallowwas studied on the basis of daily SeaWiFS ocean colour scanner data andQuickScat scatterometer wind data collected from 1999 to 2004 in the southernCaspian Sea, where the deep basin borders a vast shallow west of the shore ofmeridional extent. It was found that radiance distributions, clustered bywind rhumbs, exhibited different long-term mean patterns for winds of opposingdirections: within the shallow's boundaries, the radiances were about twice ashigh for winds having an offshore component with reference to the onshore windconditions. The zonal profile of radiance across the shallow resembleda closed loop whose upper and lower branches corresponded to the offshore and onshore winds respectively. Theloop was the most pronounced at sites with 10-15 m of water for any wavelengthof light, including the red region. On the basis of specific features of the studyarea, we attributed this pattern to sunlight backscattered from bottom sedimentsresuspended by bottom compensation currents induced by the offshorewinds