Regional Models for High-Resolution Retrieval of Chlorophyll a and TSM Concentrations in the Gorky Reservoir by Sentinel-2 Imagery

Abstract

The possibilities of chlorophyll a (Chl a) and total suspended matter (TSM) retrieval using Sentinel-2/MSI imagery and in situ measurements in the Gorky Reservoir are investigated. This water body is an inland freshwater ecosystem within the territory of the Russian Federation. During the algal bloom period, the optical properties of water are extremely heterogeneous and vary on scales of tens of meters. Additionally, they vary in time under the influence of currents and wind forcing. In this case, the usage of the traditional station-based sampling to describe the state of the reservoir may be uninformative and not rational. Therefore, we proposed an original approach based on simultaneous in situ measurements of the remote sensing reflectance by a single radiometer and the concentration of water constituents by an ultraviolet fluorescence LiDAR from a high-speed gliding motorboat. This approach provided fast data collection including 4087 synchronized LiDAR and radiometric measurements with high spatial resolutions of 8 m for two hours. A part of the dataset was coincided with Sentinel-2 overpass and used for the development of regional algorithms for the retrieval of Chl a and TSM concentrations. For inland waters of the Russian Federation, such research was performed for the first time. The proposed algorithms can be used for regular environmental monitoring of the Gorky Reservoir using ship measurements or Sentinel-2 images. Additionally, they can be adapted for neighboring reservoirs, for example, for other seven reservoirs on the Volga River. Moreover, the proposed ship measurement approach can be useful in the practice of limnological monitoring of inland freshwater ecosystems with high spatiotemporal variability of the optical properties.

Using Copernicus Sentinel-2 and Sentinel-3 data to monitor harmful algal blooms in Southern Chile during the COVID-19 lockdown

“…Minimum values were encountered for non-bloom pixels. Similar reflective spectra in the red-edge bands have also been observed by several researchers and have usually been associated with algal blooms (Gower et al, 2005;Gower et al, 2008;Hunter et al, 2010;Toming et al, 2016;Molkov et al, 2019). Kim et al (2016) carried out an optical discrimination of Cochlodinium polykrikoides in Korean waters, through the spectral response of the algae, using the same criteria.…”

Validation and Comparison of Water Quality Products in Baltic Lakes Using Sentinel-2 MSI and Sentinel-3 OLCI Data

“…It is a good start for releasing inland water quality products but might not be enough for most of the national monitoring services, which need higher spatial resolution and more different water quality products (e.g., SD and TSM). Although, MSI was initially planned only for land monitoring, already several studies have shown its suitability for water monitoring [31][32][33][34]. Also, current studies can be considered as a step toward the development of the suitable algorithms and methods for inland water monitoring with MSI.…”

Temporal and Spatial Variations of Secchi Depth and Diffuse Attenuation Coefficient from Sentinel-2 MSI over a Large Reservoir

“…The Sentinel-2 mission from the European Space Agency (ESA) is a land monitoring constellation of two satellites (S2A launched in June 2015 and S2B launched in March 2017) that provide high-resolution optical imagery (spatial resolution between 10 m and 60 m, depending on the spectral band) and presents a systematic global coverage of two to three days at mid-latitudes, which brought a great opportunity to study inland reservoirs. Several studies have been done in recent years in the analysis of water quality of inland waters using Sentinel-2 data, to measure water quality parameters of bodies of water [26][27][28][29][30][31].…”