Influence of dust and sulfate aerosols on ocean color spectra and chlorophyll a concentrations derived from SeaWiFS off the U.S. east coast
Influence of dust and sulfate aerosols on ocean color spectra and chlorophyll a concentrations derived from SeaWiFS off the U.S. east coast
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DOI：
10.1029/2000jc000555
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发表时间：
2003-06
影响因子：
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通讯作者：
S. Schollaert;J. Yoder;J. O’Reilly;D. Westphal
中科院分区：
文献类型：
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作者：
S. Schollaert;J. Yoder;J. O’Reilly;D. Westphal
[1]在美国东海岸的马尾藻副热带环流西部考察了两种主要气溶胶物种对卫星海洋颜色反演的影响。在叶绿素浓度很低的水域，归一化离水辐射(NLW)光谱以蓝色最高，并随着波长的增加而单调下降。对于叶绿素浓度低于0.13mgm−3的水体，我们比较了1999年3月至2000年3月期间不同气溶胶条件(晴朗、尘埃和硫酸盐为主)下的海景广视场传感器(SeaWiFS)的非视场光谱。经过适当的大气校正，卫星获取的NLW光谱应该对大气气溶胶的存在不敏感，但我们发现SeaWiFS光谱对气溶胶的种类和光学厚度很敏感。SeaWiFS生物光学叶绿素算法使用NLW(λ)/NLW(555)波段比率(其中λ=443、490或510 nm)：波段比率中的任何偏差都会导致错误的叶绿素浓度估计。当气溶胶可以忽略时，NLW光谱在443-510 nm范围内与现场参考数据一致。随着沙尘事件期间气溶胶光学厚度的增加(最常见的是在夏季)，NLW光谱被降低到412到510 nm之间，降低了NLW(λ)/NLW(555)波段的比率，导致人为地提高了对叶绿素a的估计。硫酸盐占主导地位的像素与412至555 nm之间的NLW光谱升高有关。硫酸盐光学厚度的增加对应于555 nm处生物光谱带比率的降低，这也使叶绿素a的估计值偏高。硫酸盐对海洋颜色反演的影响比美国东海岸的粉尘更成问题，因为硫酸盐几乎一直存在，以及通常共存的污染物气溶胶，扰乱了大气校正算法。
[1] The influence of two dominant aerosol species on satellite ocean color retrievals is examined off the U.S. East Coast in the western Sargasso subtropical gyre. Waters of very low chlorophyll concentration have normalized water-leaving radiance (nLw) spectra highest in blue and decreasing monotonically with increasing wavelength. For water with chlorophyll concentrations less than 0.13 mg m−3 we compared the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) nLw spectra for different aerosol conditions (clear, dust-dominated, and sulfate-dominated) over 1 year between March 1999 and March 2000. With appropriate atmospheric correction, satellite-derived nLw spectra should be insensitive to the presence of atmospheric aerosols, but we found the SeaWiFS spectra to be sensitive to the species and optical thickness of aerosols. The SeaWiFS bio-optical chlorophyll algorithms use nLw(λ)/nLw(555) band ratios (where λ = 443, 490, or 510 nm): any biases in the band ratios result in incorrect chlorophyll concentration estimates. When aerosols were negligible, nLw spectra were consistent with in situ reference data between 443 and 510 nm. With increasing aerosol optical thickness during dust events, most common during summer, the nLw spectra were lowered between 412 and 510 nm, decreasing nLw(λ)/nLw(555) band ratios and resulting in artificially high chlorophyll a estimates. Sulfate-dominated pixels were associated with elevated nLw spectra between 412 and 555 nm. Increasing sulfate optical thickness corresponded to decreases of the bio-optical band ratios because of the increase at 555 nm, which also biased the chlorophyll a estimates high. The effect of sulfate upon ocean color retrievals is more problematic than dust off the U.S. east coast because of the nearly constant presence of sulfate along with commonly colocated pollutant aerosols that confound atmospheric correction algorithms.