Wei Jianwei, Wang Menghua, Lee Zhongping, Ondrusek Michael, Zhang Shuai, Ladner Sherwin
Opt Express. 2021 Jan 18;29(2):2780-2797. doi: 10.1364/OE.413784.
The on-water radiometric approach employs a unique provision to obtain water-leaving radiance from nadir (Lw(λ)) which can be used for the calibration of ocean color satellites. In this effort, we address the measurement precision associated with Lw(λ) from a single on-water instrument, which is an important aspect of measurement uncertainty. First, we estimated the precision as the ratio of the standard deviation of the means of repeated measurements to the mean of these measurements. We show that the measurement precision for Lw(λ) is within 2.7-3.7% over 360-700 nm. The corresponding remote sensing reflectance spectra (Rrs(λ)) from the same instrument also exhibit a high precision of 1.9-2.8% in the same spectral domain. These measured precisions of radiance and reflectance over the 360-700 nm range are independent of the optical water type. Second, we quantified the consistency of on-water Lw(λ) and Rrs(λ) from two collocated systems for further insight into their measurement repeatability. The comparison reveals that Lw(λ) measurements in the 360-700 nm agree with each other with an absolute percentage difference of less than 3.5%. The corresponding Rrs(λ) data pairs are subjected to increased differences of up to 8.5%, partly due to variable irradiance measurements (Es(λ)). The evaluation of measurement precision corroborates the reliability of the on-water acquisition of radiometric data for supporting satellite calibration and validation.
水上辐射测量方法采用了一种独特的手段来获取来自天底的离水辐射率（Lw(λ)），该辐射率可用于海洋颜色卫星的校准。在此工作中，我们探讨了与单个水上仪器测量的Lw(λ)相关的测量精度，这是测量不确定度的一个重要方面。首先，我们将精度估计为重复测量均值的标准偏差与这些测量均值的比值。我们表明，在360 - 700纳米范围内，Lw(λ)的测量精度在2.7% - 3.7%以内。同一仪器对应的遥感反射率光谱（Rrs(λ)）在相同光谱域也表现出1.9% - 2.8%的高精度。在360 - 700纳米范围内这些测得的辐射率和反射率精度与光学水型无关。其次，我们对两个并置系统的水上Lw(λ)和Rrs(λ)的一致性进行了量化，以进一步了解它们的测量重复性。比较结果表明，在360 - 700纳米范围内，Lw(λ)测量值之间的绝对百分比差异小于3.5%，相互吻合。相应的Rrs(λ)数据对的差异增大到8.5%，部分原因是辐照度测量值（Es(λ)）存在变化。测量精度的评估证实了水上获取辐射测量数据用于支持卫星校准和验证的可靠性。
