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High-Resolution Global Inland Surface Water Monitoring using PlanetScope Data and Supervised Learning with Bootstrapped Noisy Labels
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  • Sayantan Majumdar,
  • Ramesh Nair,
  • Amit Kapadia,
  • Jesus Martinez Manso,
  • Cameron Bronstein,
  • Brad Neuberg,
  • Samapriya Roy,
  • Benjamin Goldenberg,
  • Justin Davis,
  • Kelsey Jordahl,
  • Ryan Smith,
  • Leanne Abraham
Sayantan Majumdar
Planet Labs, Planet Labs

Corresponding Author:[email protected]

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Ramesh Nair
Planet Labs, Planet Labs
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Amit Kapadia
Planet Labs, Planet Labs
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Jesus Martinez Manso
Planet Labs, Planet Labs
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Cameron Bronstein
Planet Labs, Planet Labs
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Brad Neuberg
Planet Labs, Planet Labs
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Samapriya Roy
Planet Labs, Planet Labs
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Benjamin Goldenberg
Planet Labs, Planet Labs
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Justin Davis
Planet Labs, Planet Labs
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Kelsey Jordahl
Planet Labs, Planet Labs
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Ryan Smith
Missouri University of Science and Technology, Missouri University of Science and Technology
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Leanne Abraham
Planet Labs
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Abstract

High-resolution mapping and monitoring of global inland surface water bodies are critical to address challenges in sustainable water management practices. Planet currently operates the largest constellation of Earth Observation satellites and collects images at very high spatial (0.5 m - 5 m) and temporal (near-daily) resolutions. Here, we use PlanetScope data (resampled to 3 m) to develop a holistic and fully automated pipeline running on the Google Cloud Platform for monitoring global inland surface water. We incorporate the openly-available Global Reservoir and Dam (GRanD) data set into a three-stage supervised learning approach which initiates with an unsupervised label-generation step consisting of k-means clustering and NIR-based thresholding. We then rank the labels generated from these steps and the water labels extracted from the latest ESRI 10 m land cover data based on image contours. The best (noisy) labels having the least number of contours from this unsupervised learning stage are bootstrapped to train a deep-learning based semantic segmentation model (U-Net) on a KubeFlow pipeline. We subsequently create a new refined dataset by using these model predictions as labels which are passed to a Stochastic Gradient Descent (SGD)-based multi-temporal supervised label refinement stage (SGD classifier running on the same label for multiple input scenes). Finally, we iterate over the SGD based-supervised and U-Net-based label refinement steps to successively denoise the bootstrapped data until we obtain an acceptable test accuracy (F1 score > 0.9). Visual inspection of the results obtained over different climatic regions, terrains, and seasons across the globe shows that our approach works quite well. We also aggregate these predictions to detect temporal changes in surface water area. However, the model predictions exhibit high uncertainty in agricultural areas and complex terrains characterized by hill shadows and clouds. This issue could potentially be mitigated using hard-negative mining. Nevertheless, with the nearly-daily imaging capability of Planet, the high-fidelity surface water maps developed using this proposed supervised learning approach could be beneficial to the global water community for dealing with water security issues as part of the UN sustainable development goals.