Preliminary evaluation of Sentinel-derived Turbidity and SPM products in Tagus river Estuary

SA, C.; DOGLIOTTI, A. I.; SENT, G.

Milano (Italia)

Simposio; 2019 Living Planet Symposium; 2019

Suspendedparticulate matter (SPM) is one of the main water constituents in estuaries andalong with turbidity (T), which is highly correlated with SPM concentration, arekey parametersto evaluate water quality. Ocean color remote sensing has beenshown to be a useful tool to map turbidity and SPM concentration over coastalwaters, and different algorithms to retrieve these parameters from waterreflectance have already been developed. However, SPM algorithms usuallyrequireregional calibrationsto take into accountlocal differencesin particletype (size and composition). In the present work, in situ data (including T, SPM and radiometry measurements) were collectedat a pontoon in Tagus estuary (Portugal), between the 27th August tothe 7th September 2018, to test different algorithms (e.g. Nechadet al. 2016, Dogliotti et al. 2015) and evaluate coincident Sentinel 2 (S-2)and Sentinel-3 (S-3) imagery estimates using two different processors [i.e.ACOLITE (only S-2) and C2RCC (S-2 and S-3)]. Turbidity and SPM values variedbetween 1.49 ? 6.88 NTU and 1.3-8.3 mg/L, respectively, variability mainlyassociated with the tidal conditions. The low number of cloud-free contemporaryimages (S-2, n=2 and S-3, n=1) does not allow any robust statistics, butprovides a first preliminary validation of S-2 and S-3 data for the Tagus area.For S-2, ACOLITE processor retrieved higher reflectance values at 665, pw(665), wavelength used forSPM and T retrieval, while C2RCC processor underestimated it in comparison to in situ radiometric data. For the S-3match-up, only C2RCC processor was compared and also underestimated in situpw(665). RegardingSPM retrievals, using ACOLITE (v20180925.0)and Nechad et al. (2016) algorithms overestimated in situ values, particularly at low SPM concentrations. C2RCC alsoprovided higher SPM concentration values, for both S-3 and S-2 match-ups,except for the conditions of lower in situSPM values, where a slight underestimation was observed. Considering S-2derived turbidity, ACOLITE processor using both Nechad et al. 2016 andDogliotti et al. 2015 algorithms were tested, showing the latter betterresults. Applying the same algorithms to C2RCC-derived reflectances, resultswere underestimated for both sensors data.This workis a first Sentinel validation effort for the area, further and regularsampling should be pursued in the future in order toincrease the database, essential for algorithm development and validationactivities of satellite products for the region. This activity was conducted inthe framework of PLATAGUS, a bilateral cooperation between Portugal andArgentina (FCT-MinCyT).