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Special issue Moving Forward on Remote Sensing of Sea Surface Salinity.-- 24 pages, 14 figures, supplementary materials https://www.mdpi.com/article/10.3390/rs14020423/s1.-- Data Availability Statement: Data sharing not applicable, Salinity is one of the oldest parameters being measured in oceanography and one of the most important to study in the context of climate change. However, its quantification by satellite remote sensing has been a relatively recent achievement. Currently, after over ten years of data gathering, there are still many challenges in quantifying salinity from space, especially when it is intended for coastal environments study. That is mainly due to the spatial resolution of the available products. Recently, a new higher resolution (5 km) L4 SMOS sea surface salinity (SSS) product was developed by the Barcelona Expert Center (BEC). In this study, the quality of this product was tested along the Western Iberian Coast through its comparison with in situ observations and modelled salinity estimates (CMEMS IBI Ocean Reanalysis system). Moreover, several parameters such as the temperature and depth of in situ measurements were tested to identify the variables or processes that induced higher errors in the product or influenced its performance. Lastly, a seasonal and interannual analysis was conducted considering data between 2011 to 2019 to test the product as a potential tool for long-term studies. The results obtained in the present analysis showed a high potential of using the L4 BEC SSS SMOS product in extended temporal and spatial analyses along the Portuguese coast. A good correlation between the satellite and the in situ datasets was observed, and the satellite dataset showed lower errors in retrieving coastal salinities than the oceanic model. Overall, the distance to the coast and the closest rivers were the factors that most influenced the quality of the product. The present analysis showed that great progress has been made in deriving coastal salinity over the years and that the SMOS SSS product is a valuable contribution to worldwide climatological studies. In addition, these results reinforce the need to continue developing satellite remote sensing products as a global and cost-effective methodology for long-term studies, This work was conducted within the framework of the project AQUIMAR—Marine Knowledge Supporting Aquaculture (MAR-02.01.01-FEAMP-0107), funded by the Mar 2020—Operational Program Mar2020. B.B. was funded by a grant from Mar2020 under AQUIMAR project and also by a PhD grant awarded by Fundação para a Ciência e a Tecnologia (FCT) within the scope of the MIT Portugal Program. A.C.B. was funded by FCT through the Scientific Employment Stimulus Programme (CEECIND/0095/2017). A.T. was funded by Project SARDINHA2020 (MAR-01.04.02-FEAMP-0009), funded by the Operational Program Mar2020. This work benefited from the Infrastructure CoastNet (http://geoportal.coastnet.pt, accessed on 30 September 2021), funded by FCT and the European Regional Development Fund (FEDER), through LISBOA2020 and ALENTEJO2020 regional operational programs, in the framework of the National Roadmap of Research Infrastructures of strategic relevance (PINFRA/22128/2016). This study also received further support from FCT through MARE’s strategic program (UID/MAR/04292/2019). This work represents a contribution to CSIC Thematic Interdisciplinary Platform PTI Teledetect, with the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). This publication was also funded by the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement N810139: Project Portugal Twinning for Innovation and Excellence in Marine Science and Earth Observation—PORTWIMS

Monitoring water quality parameters and their ecological effects in transitional waters is usually performed through in situ sampling programs. These are expensive and time-consuming, and often do not represent the total area of interest. Remote sensing techniques offer enormous advantages by providing cost-effective systematic observations of a large water system. This study evaluates the potential of water quality monitoring using Sentinel-2 observations for the period 2018-2020 for the Sado estuary (Portugal), through an algorithm intercomparison exercise and time-series analysis of different water quality parameters (i.e., colored dissolved organic matter (CDOM), chlorophyll-a (Chl-a), suspended particulate matter (SPM), and turbidity). Results suggest that Sentinel-2 is useful for monitoring these parameters in a highly dynamic system, however, with challenges in retrieving accurate data for some of the variables, such as Chl-a. Spatio-temporal variability results were consistent with historical data, presenting the highest values of CDOM, Chl-a, SPM and turbidity during Spring and Summer. This work is the first study providing annual and seasonal coverage with high spatial resolution (10 m) for the Sado estuary, being a key contribution for the definition of effective monitoring programs. Moreover, the potential of remote sensing methodologies for continuous water quality monitoring in transitional systems under the scope of the European Water Framework Directive is briefly discussed.

Ocean color of tropical lagoons is dependent on bathymetry and bottom type, as well as input of coastal living and mineral particles and chromophoric dissolved organic matter (CDOM). The New Caledonia lagoon lies in the Southwestern Tropical Pacific around 21° 30’S and 166° 30’E, with a great marine biodiversity in UNESCO Heritage coral reefs, benthic sea grass, and benthic communities. They are largely connected to the open ocean in the southern and eastern parts, but only by narrow passes in the southwest part. The trophic state is linked to spatial variations in flushing times. High run offs due to rain carrying abundant chromophoric dissolved organic matter (CDOM) and particle loads may greatly impact the functioning of ecosystems while rivers and sewage effluents may induce localized impacts. Two oceanographic cruises (CALIOPE 1 in 2011 and CALIOPE 2 in 2014) were carried out off the Eastern Coast of New Caledonia during a calm dry period and during high winds, respectively. Multi- and hyper-spectral marine reflectance was measured with a SIMBADA instrument and a TRIOS radiometer system, together with inherent optical properties (total and CDOM absorption coefficients with a PSICAM, in situ absorption and scattering with an AC9, backscattering with a Hydroscat-6). Fluorescence of CDOM (EEM/PARAFAC) was measured on collected 0.2 μm filtered samples. In 2014, Satlantic and FieldSpec hyper-spectral radiometers were available for in-water profiling of upwelling radiance and downwelling irradiance and above-water reflectance measurements, respectively. Inherent and apparent optical data from the two cruises are compared and used to estimate ocean color algorithms performance and evaluate a Linear Matrix Inversion method, providing tools for remote sensing on this highly under-sampled coastal region of New Caledonia.

The spatial and seasonal variations of the micro-zooplankton abundance in a subtropical estuary were studied during a year. Five sampling sites were monthly sampled in Guaratuba Bay, Paraná State, from September 2004 to July 2005. The microzooplankton was sampled in the water subsurface with suction pump and filtered in 64μm plankton net. The environmental variables was gotten with a multiparameter Horiba U10 (salinity, dissolved oxygen, temperature and pH), and Secchi disk (transparency). The cluster similarity analysis grouped zooplankton in freshwater, summer meroplanktonic organisms and holoplanktonic contend different ontogenetic stages. The distinct groups among stations sampling occurred for the high proximity of the tributaries discharges or in function of the linking of the estuary with the ocean. Between the months, the seasons had been separate. The canonical correlation analysis (81% of explanation) complemented the results of the analysis of grouping, separating seasonally and spatially the main groups and its abundance. The results suggest clear space and seasonal variations for the micro-zooplankton in the Guaratuba Bay, with peaks of abundance in the summer due to meroplankton contribution associated to the highest water temperatures. Copepoda had dominated numerically under other groups, mainly the immature forms, sufficiently showed in reason of the small opening mesh of the employed net., Foram estudadas as variações espaciais e temporais da abundância do micro-zooplâncton em um estuário subtropical, com auxílio de análises multivariadas. Utilizou-se análise de agrupamento por similaridade com índice de Bray Curtis sobre a abundância dos grupos zooplanctônicos, pontos e meses; e análise de correlação canônica - ACC da abundância com variáveis ambientais mensuradas. Mensalmente, de setembro/04 a julho/05, foram amostrados cinco pontos na baía de Guaratuba, Paraná. Na sub-superfície da água o zooplâncton foi coletado com moto-bomba, filtrado em rede cônica de 64μm, e as variáveis ambientais obtidas com uma sonda Horiba U10 (salinidade, oxigênio dissolvido, temperatura e pH), e com imersão do disco de Secchi (transparência). A análise de similaridade agrupou o zooplâncton em organismos límnicos, meroplanctônicos especialmente de verão e holoplanctônicos contendo diferentes estágios ontogênicos. A formação de distintos agrupamentos entre os pontos de coleta ocorreu pela maior proximidade das descargas dos tributários ou em função da ligação do estuário com o oceano. Entre os meses, as estações do ano foram separadas. A ACC (91% de explicação) complementou os resultados da análise de agrupamento, separando espaço temporalmente os principais grupos quanto à abundância. Os resultados sugerem nítidas variações espaciais e temporais para o micro-zooplâncton na baía de Guaratuba, com picos de abundância no verão devido à contribuição do meroplâncton associado às maiores temperaturas da água. Os copépodes dominaram numericamente sob os demais grupos estuarinos, principalmente as formas imaturas, bastante amostradas em razão da pequena abertura de malha da rede empregada.