Feasibility of PlanetScope SuperDove constellation for water quality monitoring of inland and coastal waters

Sakib Kabir¹Arun Muralidharan Saranathan¹Brian Barnes²Akash Ashapure^1*Ryan E O'shea¹Victoria G Stengel³

• ¹Science Systems and Applications, Inc., Lanham, United States
• ²College of Marine Science, University of South Florida, St. Petersburg FL, United States
• ³U.S. Geological Survey Geology, Energy and Minerals Science Center, Austin TX, United States

Planet's SuperDove (SD) sensors offer eight bands (seven visible, one near infrared (NIR)) at 3 m spatial and near-daily temporal resolution. The yellow (610 nm) and red-edge (705 nm) bands are valuable for retrieving water quality (WQ) parameters, supporting applications such as harmful algal bloom (HAB) and post-disaster monitoring. To enable scientific use, we assess signal-to-noise ratios (SNRs), with the highest (248:1) at 443 nm and the lowest (8:1) at 865 nm, and other visible bands ranging from 26:1-98:1. We cross-calibrated SD with Sentinel-2 Multi-Spectral Imager (MSI) using near-simultaneous observations over aquatic environments by comparing top-of-atmosphere (TOA; 𝜌 𝑡 ) reflectance across five shared visible bands (443, 490, 565, 665, and 705 nm), and derived calibration coefficients through linear regression. Before calibration, SD-MSI median 𝜌 𝑡 differences ranged from ~0.7-13%, with highest differences at 705 nm. After applying the calibration, these differences reduced to -0.07 to -2.2%, including improvements at 665 nm (from ~8% to -2.2%) and 705 nm (from ~13% to -0.1%). Differences in atmospherically corrected remote sensing reflectance (𝑅 𝑟𝑠 ) also decreased from 16-95% to 8-72% post-calibration, with 565 nm showing the lowest (~8%) and 705 nm the highest (~72%) residual difference. Remaining 𝑅 𝑟𝑠 discrepancies are attributed in part to SD's inter-sensor differences and uncertainties in atmospheric correction. We qualitatively compared chlorophyll-a (Chla) and Secchi-disk depth (𝑍 𝑠𝑑 ) WQ products from SD and MSI, including a time-series analysis focused on the Dixie Fire and subsequent algal bloom in Lake Almanor (Sept-Dec 2021). The products captured expected trends, highlighting SD's potential for WQ monitoring, while elevated uncertainties in 𝜌 𝑡 and 𝑅 𝑟𝑠 suggest the need for improved calibration stability and atmospheric correction.