Optical water characterization and atmospheric correction assessment of estuarine and coastal waters around the AERONET-OC Bahia Blanca

ARENA MAXIMILIANO; PRATOLONGO PAULA; LOISEL HUBERT; TRAN DUY MANH; JORGE DANIEL; DELGADO ANA LAURA

Frontiers in Remote Sensing

Frontiers

Lugar: Nebrasca ; Año: 2024 vol. 5

2673-6187

The site AERONET-OC Bahía Blanca (BB-AERONET-OC) is located at the mouthof the Bahía Blanca Estuary, Argentina (Southwestern Atlantic Ocean), a coastalsystem defined by its high suspended loads and relatively low colored dissolvedorganic matter. The typically high turbidity of these waters makes the BBAERONET-OC distinctive within the AERONET-OC network stations, providingexceptional opportunities not only for the validation of atmospheric correctionalgorithms but also for the development of regional algorithms for coastalcomplex waters. A SeaWiFS Photometer Revision for Incident SurfaceMeasurements (SeaPRISM) instrument was deployed in January 2020 in theupper rail of a Mareograph Tower, a 15m tall structure, located 10 miles awayfrom the coast in optically deep waters. In this work we used the remote sensingreflectance (Rrs) derived from the BB-AERONET-OC measurements along with insitu hyperspectral radiometric data to classify optical water types (OWTs). Weassigned each Rrs(λ) spectra to one of the five OWTs defined by Tran et al.(Remote Sensing, 2023, 15 (6), 1653), and OWTs were further characterized withthe concentrations of optically significant components (chlorophyll-a andsuspended particulate matter) and inherent optical properties (absorptions ofphytoplankton, non-algal particles, and dissolved organic matter), retrieved fromwater samples obtained simultaneously with radiometric spectra. Based on amatch-up exercise with in situ data, different schemes of atmospheric correctionmethods were applied to Sentinel-3 Ocean and Land Colour Instrument (OLCI)images. The operational product OLCI Level 2 European Space Agency (ESA)standard (hereafter referred to as “Standard Neural Network (NN)”) proves to bethe most suitable atmospheric correction algorithm, which was then used todescribe spatial patterns and temporal variability of the different OWTs in theregion. The BB-AERONET-OC site is located in a sharp transition betweenestuarine and coastal waters that present contrasting optical conditions: OWT4 dominates over time (73.72% of the observations), followed by OWT 3 (24.74%)and OWT 5 (1.53%). OWTs 4 and 5 are associated with turbid waters of the BahíaBlanca Estuary, especially OWT 5, which typifies the very turbid waters from the inner estuary, with the particulate load dominated by mineral sediments anddetritus. OWT 3, in turn, depicts the eutrophic coastal waters of the inner shelf.The variability of OWTs and the relative contribution of organic and inorganiccompounds to the suspended material would be mostly related with theprevalence of northwest winds in the area, which would drive the export of estuarine sediments to the shelf.