The case-1 (optically simple) oceanic environment is described by a smoothly transitioning gradient in optical properties arising from the concentration of the primary algal photopigment, chlorophyll a, plus its covarying and optically relevant constituents. As such, the spectral transition that defines case-1 water types is captured by a single primary spectral mode—the transition in peak wavelength between oligotrophic blue and mesotrophic green waters—which has substantiated blue-green algorithm designs and sensor capabilities for oceanographic observations that primarily focus on retrieving the visible (VIS) spectral domain. For case-2 water types, e.g., optically complex inland and coastal waters interacting with the continent and shelf, a similar unifying mode that captures common spectral changes is not defined. This study evaluates the potential to formulate optical complexity as a progression of discrete or continuous parameters in order to advance radiometry for a global range of water types. Within a gradient of increasing optical complexity, this study uses a comprehensive set of case-2 scenarios to compare spectral changes as a function of increasing water mass complexity, based on simple diagnostic tools and definitions. The spectral comparisons rely on instrument and data processing improvements—developed from an end-member analysis (EMA) perspective—that optimize a spectral domain spanning wavelengths shorter and longer than the primarily case-1 VIS domain, i.e., the ultraviolet (UV) and near-infrared (NIR) domains, and that enable sampling of shallow or non-navigable water bodies. The spectral comparisons in the case-2 scenarios indicate five primary modes capture the dominant spectral changes associated with increasing optical complexity. The primary modes and diagnostic tools presented herein enable the organization of global (i.e., oceanic, coastal, and inland) water bodies along a continuous complexity gradient defined by optical complexity instead of as a binary and discontinuous partition (i.e., case-1 and case-2). The expression and dynamic range of the modes establish the spectral regions most sensitive to water mass transitions in optically complex environments. These spectral expressions provide a basis for evaluating the spectral sensing requirements for next-generation remote sensing missions, which seek to characterize optically complex coastal (i.e., the continental shelf and its environs) and inland water bodies. In particular, three of five spectral modes indicate the spectral response to increasing optical complexity is greatest at the spectral end members. The results presented indicate that both discretized values and a continuum are useful for formulating a hierarchy in optical complexity and suggest next-generation activities should optimize the retrieval of the UV and NIR domains for improving the development of global algorithms.

案例1（光学上简单）的海洋环境是由主要藻类光敏色素叶绿素a的浓度引起的光学特性的平稳过渡梯度来描述的，以及其可变的和与光学相关的组成部分。这样，定义案例1水类型的光谱跃迁可以通过单一的主要光谱模式（贫营养蓝水和中营养绿水之间的峰值波长跃迁）来捕获，该模式具有充分的蓝绿色算法设计和用于海洋观测的传感器功能，主要侧重于检索可见（VIS）光谱域。对于案例2的水类型，例如与大陆和陆架相互作用的光学复杂的内陆和沿海水域，未定义捕获常见光谱变化的相似统一模式。这项研究评估了将光学复杂性公式化为离散或连续参数的过程的潜力，以促进全球范围内各种水类型的辐射测定。在简单的诊断工具和定义的基础上，这项研究使用了一系列复杂的案例2场景，以比较光谱变化作为增加水质量复杂性的函数，在逐渐增加的光学复杂性的梯度范围内。光谱比较依赖于仪器和数据处理方面的改进（从最终成员分析（EMA）的角度出发），该改进优化了一个光谱域，该光谱域的波长比主要是case-1 VIS域短和长，即紫外线（UV）和紫外光谱。近红外（NIR）域，可以对浅水区或不可通航的水体进行采样。在案例2场景中的光谱比较表明，五种主要模式捕获了与增加的光学复杂性相关的主要光谱变化。本文介绍的主要模式和诊断工具使全球（即海洋，沿海和内陆）水体能够沿着由光学复杂度定义的连续复杂度梯度进行组织，而不是作为二元和不连续的分区（即案例1和案例） -2）。模式的表达和动态范围建立了对光学复杂环境中水质跃迁最敏感的光谱区域。这些光谱表达式为评估下一代遥感任务的光谱传感要求提供了基础，该任务旨在表征光学复杂的沿海地区（即大陆架及其周围地区）和内陆水体。特别地，五个光谱模式中的三个指示在光谱末端成员处对增加的光学复杂性的光谱响应最大。