海中气泡对近红外波段遥感反射比的影响

The Effects of Bubbles in Seawater on the Remote Sensing Reflectance in the Near Infrared Band

海中气泡在上层海洋无处不在,风浪破碎是其主要成因,它们对光的后向散射具有较强的作用。基于Mie散射理论和遥感反射比模型,计算了不同浓度海中气泡对近红外波段遥感反射比的贡献,及其对气泡浓度N0和叶绿素a浓度[chl-a]的响应。海中气泡考虑了清洁气泡和附着有机物膜气泡两种情况。计算结果表明,大多数情况下海中气泡引起的近红外波段遥感反射比相对变化较大,最大可达30多倍(N0=107m-3,[chl-a]=0.05 mg/m3、附着有机物膜气泡的情况)。而且,气泡浓度越大、叶绿素a浓度越低,海中气泡对近红外波段遥感反射比Rrs(NIR)的影响越大。仅当N0=105m-3时清洁气泡对近红外波段遥感反射比的贡献可忽略不计。因此,当海中气泡存在时,基于暗像素假设(即假设近红外波段反射比为0)的海色遥感大气校正算法需要修正海中气泡的影响。

Ubiquitous bubbles in surface ocean are mainly generated by wind-wave breaking, which have strong effects on the back scattering of light. Based on the Mie Scattering Theory, this paper calculates the contributions of bubbles with different concentrations on the remote sensing reflectance in the near infrared band, as well as their responses on the bubble concentration N0 and chlorophyll-a concentration [chl-a]. Clean bubbles and bubbles with adhering organic films are both taken into account. The calculation results show that in most cases, the relative variation of remote sensing reflectance in the near infrared band（ Rrs（NIR）） generated by bubbles in seawater is obvious, with its maximum reaching over 30 times（N0=107m-3, [chl-a]=0.05 mg/m3, with adhering organic films）.Besides, as bubble concentration increases, [chl-a] lowers, and the effects of bubbles on Rrs（NIR） are more significant. Only when N0=105m-3, the contribution of clean bubbles on Rrs（NIR） is negligible. Therefore, when bubbles exist in seawater, correction of bubble effects is necessary for the atmospheric correction of ocean color remote sensing based on dark pixel hypothesis（assuming Rrs（NIR）=0）.