Opt Express. 2023 Apr 24;31(9):13851-13874. doi: 10.1364/OE.483418.
Planet's SuperDove constellation is evaluated for remote sensing of water targets. SuperDoves are small satellites with on board eight band PlanetScope imagers that add four new bands compared to the previous generations of Doves. The Yellow (612 nm) and Red Edge (707 nm) bands are of particular interest to aquatic applications, for example in aiding the retrieval of pigment absorption. The dark spectrum fitting (DSF) algorithm is implemented in ACOLITE for processing of SuperDove data, and its outputs are compared to matchup data collected using an autonomous pan-and-tilt hyperspectral radiometer (PANTHYR) installed in the turbid waters of the Belgian Coastal Zone (BCZ). Results for 35 matchups from 32 unique SuperDove satellites indicate on average low differences with PANTHYR observations for the first seven bands (443-707 nm), with mean absolute relative differences (MARD) 15-20%. The mean average differences (MAD) are between -0.01 and 0 for the 492-666 nm bands, i.e. DSF results show a negative bias, while the Coastal Blue (444 nm) and Red Edge (707 nm) show a small positive bias (MAD 0.004 and 0.002). The NIR band (866 nm) shows a larger positive bias (MAD 0.01), and larger relative differences (MARD 60%). Root mean squared differences (RMSD) are rather flat at around 0.01 with peaks in the bands with highest water reflectance of around 0.015. The surface reflectance products as provided by Planet (PSR) show a similar average performance to DSF, with slightly larger and mostly positive biases, except in both Green bands, where the MAD is close to 0. MARD in the two Green bands is a bit lower for PSR (9.5-10.6%) compared to DSF (9.9-13.0%). Higher scatter is found for the PSR (RMSD 0.015-0.020), with some matchups showing large, spectrally mostly flat differences, likely due to the external aerosol optical depth (τ) inputs not being representative for these particular images. Chlorophyll a absorption (a) is retrieved from PANTHYR measurements, and the PANTHYR data are used to calibrate a retrieval algorithms for SuperDove in the BCZ. Various Red band indices (RBI) and two neural networks are evaluated for a estimation. The best performing RBI algorithm, i.e. the Red band difference (RBD), showed a MARD of 34% for DSF and 25% for PSR with positive biases of 0.11 and 0.03 m respectively for 24 PANTHYR a matchups. The difference in RBD performance between DSF and PSR can be largely explained by their respective average biases in the Red and Red Edge bands, which are opposite signs for DSF (negative bias in the red), and positive for both bands for PSR. Mapping of turbid water a and hence chlorophyll a concentration (C) using SuperDove is demonstrated for coastal bloom imagery, showing how SuperDove data can supplement monitoring programmes.
对 Planet 的 SuperDove 星座进行了遥感水目标的评估。SuperDoves 是一种带有机载八波段 PlanetScope 成像仪的小型卫星，与之前几代的 Dove 相比，增加了四个新波段。黄色（612nm）和红色边缘（707nm）波段对水生应用特别感兴趣，例如在辅助色素吸收的反演中。暗光谱拟合（DSF）算法在 ACOLITE 中实现，用于处理 SuperDove 数据，其输出与在比利时沿海带（BCZ）浑浊水中安装的自主旋转和倾斜高光谱辐射计（PANTHYR）收集的匹配数据进行比较。来自 32 颗独特 SuperDove 卫星的 35 次匹配的结果表明，前七个波段（443-707nm）与 PANTHYR 观测值的平均差异较小，平均绝对相对差异（MARD）为 15-20%。对于 492-666nm 波段，平均平均差异（MAD）在-0.01 到 0 之间，即 DSF 结果显示出负偏差，而沿海蓝色（444nm）和红色边缘（707nm）显示出较小的正偏差（MAD 0.004 和 0.002）。近红外波段（866nm）显示出较大的正偏差（MAD 0.01）和较大的相对差异（MARD 60%）。均方根差异（RMSD）相当平坦，约为 0.01，在水反射率最高的波段峰值约为 0.015。Planet 提供的表面反射率产品（PSR）的平均性能与 DSF 相似，具有略大且主要为正的偏差，除了两个绿色波段外，其中 MAD 接近 0。PSR 的 MARD（9.5-10.6%）略低于 DSF（9.9-13.0%），在两个绿色波段中。PSR 的散射更高（RMSD 0.015-0.020），一些匹配显示出大的、光谱上基本平坦的差异，可能是由于外部气溶胶光学深度（τ）输入与这些特定图像不具有代表性。从 PANTHYR 测量中提取叶绿素 a 吸收（a），并使用 PANTHYR 数据在 BCZ 中校准 SuperDove 的反演算法。评估了各种红色波段指数（RBI）和两个神经网络进行估计。表现最好的 RBI 算法，即红色波段差（RBD），对于 DSF 和 PSR 的 MARD 分别为 34%和 25%，对于 24 个 PANTHYR a 匹配，正偏差分别为 0.11 和 0.03 m。DSF 和 PSR 之间 RBD 性能的差异可以很大程度上解释为它们在红色和红色边缘波段的各自平均偏差，对于 DSF 来说，这些偏差是相反的（红色的负偏差），而对于 PSR 来说，这两个波段都是正的。使用 SuperDove 对浑浊水 a 进行绘图，从而对叶绿素 a 浓度（C）进行绘图，展示了 SuperDove 数据如何补充监测计划。
