Assessing the Relative Accuracy of Planet and Sentinel-2 Derived Water Maps Using Field Data

Abstract

This study compares the accuracy of surface water maps from Sentinel-2 and Planet satellites with 43 shoreline observations on the Tanana and Willamette Rivers. High-precision GNSS rover provided the most precise results, with ~10cm accuracy. Handheld devices (BadElf: ~1m, eTrex: ~2m) were less accurate but still can be used for ground validation of satellite shorelines. For the Tanana River, Planet NDWI-derived water maps (~5m) were slightly more accurate than Sentinel-2 (~6m), despite smaller differences than their spatial resolutions. On the Willamette River, Planet achieved ~3m accuracy and Sentinel-2 ~4m accuracy using NIR-band thresholding due to minimal reflectance difference. The temporal advantage of Planet data was evident, with more clear sky observations, particularly in regions with low orbital convergence and during non-clear sky months. Despite slightly lower spatial accuracy and temporal resolution, the accessibility and reliability of Sentinel-2 data make the datasets comparable.