期刊
REMOTE SENSING
卷 11, 期 3, 页码 -出版社
MDPI
DOI: 10.3390/rs11030220
关键词
remote sensing of ocean colour; OLCI; atmospheric correction; extremely turbid waters
类别
资金
- HYPERMAQ Project through Belgian Science Policy Office [SR/00/33]
- European Space Agency under the Case2X [SEOM-DTEX-EOPS-SW-14-0002]
- National Agency for Scientific and Technological Research of Argentina [PICT 2014-0455]
A common approach to the pixel-by-pixel atmospheric correction of satellite water colour imagery is to calculate aerosol and water reflectance at two spectral bands, typically in the near infra-red (NIR, 700-1000 nm) or the short-wave-infra-red (SWIR, 1000-3000 nm), and then extrapolate aerosol reflectance to shorter wavelengths. For clear waters, this can be achieved simply for NIR bands, where the water reflectance can be assumed negligible i.e., the black water assumption. For moderately turbid waters, either the NIR water reflectance, which is non-negligible, must be modelled or longer wavelength SWIR bands, with negligible water reflectance, must be used. For extremely turbid waters, modelling of non-zero NIR water reflectance becomes uncertain because the spectral slopes of water and aerosol reflectance in the NIR become similar, making it difficult to distinguish between them. In such waters the use of SWIR bands is definitely preferred and the use of the MODIS bands at 1240 nm and 2130 nm is clearly established although, on many sensors such as the Ocean and Land Colour Instrument (OLCI), such SWIR bands are not included. Instead, a new, cheaper SWIR band at 1016 nm is available on OLCI with potential for much better atmospheric correction over extremely turbid waters. That potential is tested here. In this work, we demonstrate that for spectrally-close band triplets (such as OLCI bands at 779-865-1016 nm), the Rayleigh-corrected reflectance of the triplet's middle band after baseline subtraction (or baseline residual, BLR) is essentially independent of the atmospheric conditions. We use the three BLRs defined by three consecutive band triplets of the group of bands 620-709-779-865-1016 nm to calculate water reflectance and hence aerosol reflectance at these wavelengths. Comparison with standard atmospheric correction algorithms shows similar performance in moderately turbid and clear waters and a considerable improvement in extremely turbid waters.
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