论从遥感观测推断浮游植物特性的风险
On the Peril of Inferring Phytoplankton Properties from Remote-Sensing Observations
AI总结：
研究揭示遥感反射率反演固有光学特性时存在物理简并与统计功效限制，指出多光谱数据难以可靠检测浮游植物吸收，高光谱及NASA/PACE仅能部分改善。
摘要：
自1978年以来，遥感卫星上的传感器一直在光学波长提供全球多波段图像，以评估海洋水色。与此同时，复杂的辐射传输模型考虑了地球大气和海洋造成的衰减与发射，从而估算离水辐亮度和遥感反射率Rrs。根据这些Rrs测量值，可以推断海水的吸收和散射。我们强调，辐射传输方程中存在一种固有的物理简并性，该方程将Rrs与吸收系数a和后向散射系数b_b（即固有光学特性，IOPs）联系起来。由于Rrs仅取决于b_b与a的比值，这意味着在没有先验知识的情况下，无法反演获得非水IOPs（a_nw和b_bnw）的独立函数。此外，水通常在蓝色波长主导散射，并在红色波长主导吸收，这在存在噪声时进一步限制了IOPs的反演。我们证明，以往和当前所有多光谱卫星观测都缺乏统计功效，总共无法测量超过3个用于描述a_nw和b_bnw的参数。由于有色溶解有机物在短波长（λ<500 nm）普遍存在类指数吸收，多光谱Rrs不允许在没有非常严格先验的情况下检测浮游植物吸收a_ph。此外，此类先验会导致a_ph反演出现偏差和不确定性。高光谱观测或许能够恢复第4个、甚至可能第5个参数，但这些参数只能描述a_ph复杂性的一两个方面。这些结果使数十年来关于IOP反演的文献（包括对浮游植物生长和生物量的估算）受到质疑。我们进一步得出结论，NASA/PACE将极大增强我们测量地球浮游植物生物量的能力，但在解析IOPs方面仍存在挑战。
英文摘要：
Since 1978, sensors on remote-sensing satellites have provided global, multi-band images at optical wavelengths to assess ocean color. In parallel, sophisticated radiative transfer models account for attenuation and emission by the Earth's atmosphere and ocean, thereby estimating the water-leaving radiance or and remote-sensing reflectance Rrs. From these Rrs measurements, estimates of the absorption and scattering by seawater are inferred. We emphasize an inherent, physical degeneracy in the radiative transfer equation that relates Rrs to the absorption and backscattering coefficients a and b_b, aka inherent optical properties (IOPs). Because Rrs depends solely on the ratio of b_b to a, meaning one cannot retrieve independent functions for the non-water IOPs, a_nw and b_bnw, without a priori knowledge. Moreover, water generally dominates scattering at blue wavelengths and absorption at red wavelengths, further limiting retrievals of IOPs in the presence of noise. We demonstrate that all previous and current multi-spectral satellite observations lack the statistical power to measure more than 3 parameters total to describe a_nw and b_bnw. Due to the ubiquitous exponential-like absorption by color dissolved organic matter at short wavelengths (l<500nm), multi-spectral Rrs do not permit the detection of phytoplankton absorption a_ph without very strict priors. Furthermore, such priors lead to biased and uncertain retrievals of a_ph. Hyperspectral observations may recover a 4th and possibly 5th parameter describing only one or two aspects of the complexity of a_ph. These results cast doubt on decades of literature on IOP retrievals, including estimates of phytoplankton growth and biomass. We further conclude that NASA/PACE will greatly enhance our ability to measure the phytoplankton biomass of Earth, but challenges remain in resolving the IOPs.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
