Abstract
Abstract. Recent advancements in developing small satellites known as CubeSats provide an increasingly viable means of characterizing the dynamics of inland and nearshore waters with an unprecedented combination of high revisits (< 1 day) with a high spatial resolution (meter-scale). Estimation of water quality parameters can benefit from the very high spatiotemporal resolution of CubeSat imagery for monitoring subtle variations and identification of hazardous events like algal blooms. In this study, we present the first study on retrieving lake chlorophyll-a (Chl-a) concentration and detecting algal blooms using imagery acquired by the PlanetScope constellation which is currently the most prominent source of CubeSat data. Moreover, the concentration of total suspended matter (TSM) is retrieved that is an indicator of turbidity. The retrievals are based upon inverting the radiative transfer model. The low spectral resolution (four bands) of PlanetScope imagery poses challenges for such a physics-based inversion due to spectral ambiguities in optically-complex waters like inland waters. To deal with this issue, the number of variable parameters is minimized through inverse modeling. Given the significance of having high-quality water-leaving reflectance for physics-based models, a variable parameter (gdd) is considered to compensate for the atmospheric and sun-glint artifacts. The results compared to the in-situ data indicate high potentials of PlanetScope imagery in retrieving water quality parameters and detection of algal blooms in our case study (Lake Trasimeno, Italy).
Highlights
A new era of high spatial resolution imaging has just emerged with the launch of CubeSat satellites
High spatial and temporal resolutions of the PlanetScope constellation are very attractive for studying inland waters, the low spectral resolution poses challenges for the estimation of biophysical parameters (Niroumand-Jadidi et al, 2020c)
This is because of the spectral ambiguity resultant from the combination of various parameters that define the shape and magnitude of water-leaving spectra (Defoin-Platel and Chami, 2007). Some of these parameters are concerned with the quality of water such as chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM)
Summary
A new era of high spatial resolution imaging has just emerged with the launch of CubeSat satellites. The recent PlanetScope constellation of satellites (180+ CubeSats) has paved the way for monitoring Earth resources including inland waters with a high spatial resolution (3 m) and on a daily basis (Planet, 2020) This unprecedented spatiotemporal resolution opens up new horizons for near real-time monitoring of biophysical processes in inland waters. High spatial and temporal resolutions of the PlanetScope constellation are very attractive for studying inland waters, the low spectral resolution (four bands) poses challenges for the estimation of biophysical parameters (Niroumand-Jadidi et al, 2020c) This is because of the spectral ambiguity resultant from the combination of various parameters that define the shape and magnitude of water-leaving spectra (Defoin-Platel and Chami, 2007).
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