Validation activities and plans in a Cyanobacteria-dominated turbid lake in the Argentinean Pampa plain.

DOGLIOTTI, ANA; GOSSN, JUAN IGNACIO; SÁNCHEZ, MARÍA LAURA

Milan

Congreso; Living Planet Symposium; 2019

ESA

In any satellite mission the validation of derived products is essential to assess and ensure high-quality geophysical data products. In the frame of HYPERMAQ and HYPERNETS projects a new network of automated hyperspectral radiometers is being developed. One of the planned test sites is an eutrophic, turbid, permanently mixed shallow water body called Chascomús lake located in the Pampa Plain in the Buenos Aires Province (Argentina). This lake has been intensively studied in the last 20 years and new field campaigns have been recently performed in which radiometric measurements using TriOS/RAMSES radiometer were made for the first time. Measured hyperspectral spectra have shown a dip at 620 nm, the characteristic absorption feature of the photopigment phycocyanin (PC), a marker pigment for Cyanobacteria which presence has been confirmed by microscopy. High spectral resolution information allows for the full potential of the reflectance signal from lakes to be explored to improve the retrieval accuracy of existing products, like chlorophyll-a concentration, but also to derive new products and validate any optical mission, like S2, S3, PROBA-V, MODIS, VIIRS, L8, Pléiades, ENMAP, PRISMA, SABIA/MAR, etc. The MultiSpectral Instrument (MSI) on board of Sentinel-2 mission provides high spatial resolution data which can be relevant for monitoring coastal and in-land waters because of the high spatial resolution (10 to 20 m) and spectral bands which allows the estimation of total suspended matter and chlorophyll concentration, even though they were originally designed for land applications. In turn, OLCI on board Sentinel-3, a mission designed to monitor the ocean color, has more bands which might be capable of capturing changes in the reflectance at specific wavelengths of biological interest, like the 620 nm and close bands, but with a coarser spatial resolution (300 m) which might prevent its use in small water bodies. Even though the few existing measurements are not enough to perform a strict match-up analysis, a first evaluation of Sentinel-2 and Sentinel-3 potential use to identify cyanobacteria-dominated waters is here analyzed. Different processors, like ACOLITE and C2RCC were tested. Reflectance retrieved using ACOLITE showed better performance for bands between 510 and 680 nm, overestimating at higher and underestimating at lower wavelengths, but generally reproducing the shape of the spectra and the dip at 620 band. In turn, C2RCC systematically underestimated in situ values with better results in the blue bands compared to ACOLITE, but the dip at 620 nm and characteristic peak at 708 nm was not reproduced. For Sentinel-2 ACOLITE retrieved values tend to overestimate while C2RCC tended to underestimate field reflectance measurements, but both reproducing in general the spectral shape.