Abstract
The recent PlanetScope constellation (130+ satellites currently in orbit) has shifted the high spatial resolution imaging into a new era by capturing the Earth’s landmass including inland waters on a daily basis. However, studies on the aquatic-oriented applications of PlanetScope imagery are very sparse, and extensive research is still required to unlock the potentials of this new source of data. As a first fully physics-based investigation, we aim to assess the feasibility of retrieving bathymetric and water quality information from the PlanetScope imagery. The analyses are performed based on Water Color Simulator (WASI) processor in the context of a multitemporal analysis. The WASI-based radiative transfer inversion is adapted to process the PlanetScope imagery dealing with the low spectral resolution and atmospheric artifacts. The bathymetry and total suspended matter (TSM) are mapped in the relatively complex environment of Venice lagoon during two benchmark events: The coronavirus disease 2019 (COVID-19) lockdown and an extreme flood occurred in November 2019. The retrievals of TSM imply a remarkable reduction of the turbidity during the lockdown, due to the COVID-19 pandemic and capture the high values of TSM during the flood condition. The results suggest that sizable atmospheric and sun-glint artifacts should be mitigated through the physics-based inversion using the surface reflectance products of PlanetScope imagery. The physics-based inversion demonstrated high potentials in retrieving both bathymetry and TSM using the PlanetScope imagery.
Highlights
The PlanetScope constellation has bridged the long-lasting gap between the high spatial and the high temporal resolution of spaceborne imagers by means of more than 130 CubeSats currently in orbit [1,2]
The total suspended matter (TSM) maps derived from the shallow-water inversion are presented in Figure 2 for the periods before and during the COVID-19 lockdown
The abrupt change of TSM identified from analyzing the images before and during this benchmark event reveals the effectiveness of the physics-based approach in retrieving this constituent from PlanetScope imagery
Summary
The PlanetScope constellation has bridged the long-lasting gap between the high spatial and the high temporal resolution of spaceborne imagers by means of more than 130 CubeSats (known as Doves) currently in orbit [1,2]. The PlanetScope operated by Planet Labs, Inc. is the largest Earth-observing constellation of small satellites in the size of 10 × 10 × 30 cm carrying sensors with four or five bands [2] This high number of CubeSat imagers allows for daily acquisitions over the entire land surface of the Earth and near-shore coastal environments at the spatial resolution of about 3 m. The availability of PlanetScope imagery opens up new opportunities for a wide range of Earth observation applications by providing insights into the changes of land-cover/use and biophysical attributes with spatiotemporal details never previously possible In this context, PlanetScope constellation potentially offers a unique means of monitoring the dynamics of aquatic biophysical parameters, such as in-water constituents even for small bodies of inland water. The high revisit frequency, i.e., daily overpasses, significantly enhances the capability of capturing cloud-free imagery, which is a remarkable step toward near real-time monitoring of the inland/coastal waters [1,3,4]
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