由TSRB辐射计数据估算海面离水辐亮度的经验方法

An Empirical Method for Determining the Water Leaving Radiance from TSRB Radiometer Measurements

为建立基于经验统计的TSRB辐射计数据估算离水辐亮度的方法,利用SeaBASS数据库中640多个现场测量的辐亮度和辐照度光谱剖面数据,建立向上辐亮度衰减系数Klu的经验算法。此算法为幂指数形式,输入变量为水下0.65 m的向上辐亮度(490 nm)与海面上向下的辐照度(555 nm或665 nm)之比(即为TSRB直接测量的两个参数)。当水体较清时,输入为蓝绿波段之比,当水混浊时,采用蓝红波段之比。获得了Klu后,海面以上的辐亮度(离水辐亮度)由z=0.65 m处的辐亮度外推获得。初步的检验结果表明,该方法对一类和二类水域都有很好性能,且算法实现简单,运行速度快。

A robust and simple method to determining the water leaving radiance from the TSRB radiometer measurements has been derived. Firstly, an empirical algorithm for deriving the attenuation coefficient （Klu） of upwelling radiance from TSRB measurements has been built up from a data set of SeaBASS which contains more than 640 observations of profiles of upwelling radiance and downwelling irradiance. The proposed algorithm follows a power law. The input is the ratio of the upwelling radiance （L,） at depth of 0. 65 m at 490 nm to the downwelling irradiance （Ed） above sea surface at 555 nm or 665 nm, these two parameters are directly measured by TSRB. For the clear waters, the ratio is blue （at 490 nm） to green （at 555 nm）, for the turbid waters, the ratio is blue （at 490 nm） to red （at 665 nm）. The water leaving radiance can be derived from the radiance at depth of 0. 65 nm by the known Klu. The results show that the present method has good performance in both clear and turbid waters. Besides, it is easily reproducible, and its computing is fast.