Autonomous underwater vehicles provide water column observations of phytoplankton biomass using chlorophyll a (Chl a) fluorometers. However, under high incident light, phytoplankton fluorescence yield decreases in a process known as non-photochemical quenching, resulting in a reduced Chl a fluorescence signal. Methods have been developed to identify and remove the quenched signal from observations by autonomous underwater vehicles. These existing methods rely on assumptions of the homogeneity of the system, both in terms of time (i.e., between day and night observations) and space (i.e., within the water column or between neighboring profiles). These assumptions are not valid in shallow shelf seas or when sampling across different water masses. Thus, we evaluate six new quenching correction methods based on an existing ocean-based method, but adapted for a continental shelf sea environment where the water mass changes between night and day observations. We have included two main changes to the existing method. First, we interpolate the unquenched, nighttime signal across the daytime observations and use this as a reference for correcting the quenched, daytime signal. Second, we explore the inclusion of a fluorescence quenching depth limit. By interpolating nighttime observations across daytime periods, the diel changes in non-photochemical quenching were separated from the phytoplankton population changes. The proposed methods all show improved performance compared to existing approach. The methods presented here, and the approach used to evaluate them, are applicable in other shelf sea environments, enabling studies using autonomous Chl a fluorescence data across shelf sea ecosystems.

中文翻译：

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陆架海环境下自主水下航行器叶绿素a非光化学荧光猝灭校正方法

自主水下航行器使用叶绿素a (Chl a ) 荧光计提供浮游植物生物量的水柱观测。然而，在高入射光下，浮游植物荧光产量在称为非光化学猝灭的过程中降低，导致叶绿素a荧光信号减少。已经开发出方法来识别和消除自主水下航行器观测中的猝灭信号。这些现有方法依赖于系统均匀性的假设，无论是在时间（即白天和夜间观测之间）还是在空间（即在水柱内或相邻剖面之间）。这些假设在浅陆架海或跨不同水团采样时无效。因此，我们基于现有的基于海洋的方法评估了六种新的猝灭校正方法，但适应了大陆架海洋环境，其中水团在夜间和白天观测之间发生变化。我们对现有方法进行了两项主要更改。首先，我们在白天观测中插入未猝灭的夜间信号，并将其用作校正猝灭的白天信号的参考。其次，我们探索加入荧光猝灭深度限制。通过将夜间观测值插入白天，将非光化学猝灭的昼夜变化与浮游植物种群变化分开。与现有方法相比，所提出的方法都显示出改进的性能。这里介绍的方法以及用于评估它们的方法适用于其他陆架海洋环境，从而能够使用跨陆架海洋生态系统的自主叶绿素a荧光数据进行研究。