## Materials and Methods
### Composite Processing  
A four-band (blue, green, red, near infrared) surface reflectance composite combining over two years of observations from PS images was created for the Caribbean Basin using 38,642 scenes that were acquired between 1 October 2017 and 15 September 2019 and mosaicked using a Mercator projection. A multi-year timeframe was necessary to reduce cloud contamination and ensure adequate coverage. A best-scene compositing method was used instead of traditional pixel-based methods, since PS data do not have sub-pixel geolocation accuracy, which can cause problems when using pixel-based compositing methods [38]. Planet's best-scene approach operates by ranking all available scenes, using all valid pixels from the best scene, then filling any unfilled areas by pixels from the next best scenes in ranked order. This ensures that adjacent pixels are highly likely to have come from the same scene, mitigating geolocation differences while reducing the likelihood of artifacts due to changing sea conditions between scenes. However, this method also necessitates additional processing to remove scene edges from the final composite and requires an accurate scene ranking algorithm to avoid undesirable effects, such as waves and sunlight. To avoid atmospheric (e.g., haze, cloud cover) and oceanographic effects (e.g., sunlight, wave patterns, surf, and turbidity) during the compositing process, scenes were ranked based on a variety of metrics that are sensitive to these conditions. A linear model combining three independent cloud estimates and average gaussian gradient magnitude and \begin{table}
\begin{tabular}{c c} \hline \hline Spectral bands (nm) & Blue: 470 (455–515) \\ (Full width at half maximum (FWHM) and & Green: 540 (500–590) \\ range) & Red: 610 (590–670) \\ NIR: 790 (780–860) \\ \hline Ground sampling distance & 3.5–4.1 m \\ \hline Camera dynamic range & 12-bit \\ \hline Signal-to-noise ratio (SNR) & \textasci{-}80 \\ \hline Scene dimension (frame size) & \textasci{-}20 km \(\times\) 12 km \\ \hline Geometric accuracy (horizontal) & \textasci{-}10 m \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical specifications of PlanetScope (PS) Dove Classic imagery (adapted from [37]). Figure 2: Relative Spectral Response (RSR) of the PlanetScope (PS) Dove four multispectral bands (adapted from [37]). brightness was used to find scenes most likely to yield clear seabed observations. Two of the cloud estimates incorrectly classified surf and sunglint as clouds and were, therefore, used to identify poor quality scenes. Scenes yielding a low average gaussian gradient magnitude were likely to have been acquired on calm days with low surface roughness (i.e., waves). Darker scenes were more likely to be less turbid with low atmospheric haze. The model was trained on hand-ranked lists of overlapping scenes in a variety of coastal and open water areas to find optimal weights for each of these input parameters. Due to the relatively low tidal amplitude in the Caribbean (\(\sim\)0.5 m), scenes were not filtered based on the tidal stage, since differences in water depth and exposed area are minimal. PS surface reflectance data contain a high degree of scene-to-scene variability, since the process relies on Moderate Resolution Imaging Spectroradiometer (MODIS)-based atmospheric optical depth estimates collected at a different time and at a lower spatial resolution [39]. Additionally, PS data have a significantly different spectral response than MODIS or other common imaging platforms (Figure 3a). Therefore, each PS scene was empirically normalized to MODIS MOD9A1 reference data in addition to the physics-based atmospheric correction approach used in the PS surface reflectance scene product. The normalization takes the form of a linear Spatial Band Adjustment Factor (SBAF) for each band and is applied uniformly to the entire scene (Figure 3b) [40]. However, the SBAFs are calculated independently for each scene, rather than on a per-satellite or per-constellation basis.