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Using MERIS data to assess the spatial and temporal variability of phytoplankton in coastal areas
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0003-3777-6788
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

This study evaluates the use of MERIS data (2003-2011) in coastal zone monitoring using Himmerfjärden bay as an example.  The bay is one of the most frequently monitored coastal areas in the world, allowing for a rigorous comparison between satellites and ship-based monitoring data. The validity of the processors used in the study have been previously assessed and include correction for adjacency effects from land.  Furthermore, a new set of rigorous coastal flags developed by the ESA CoastColour project was applied to assure good data quality in the coastal zone.

MERIS data was used for the integration of chlorophyll a over each water body in the Himmerfjärden area, following the national water body classification by the Swedish Meteorological and Hydrological Institute (SMHI). Hovmöller diagrams were derived for different water bodies along a coastal gradient in order to display the phenology of phytoplankton in each water body.  The Hovmöller diagrams were directly compared to the phenology graphs derived from ship-based in situ sampling. While increasing both the temporal and spatial resolution of chlorophyll data, MERIS satellite data can also be used to evaluate how representative in situ monitoring stations are for a given water body.

Chlorophyll a anomaly maps were produced for the bay and its adjacent areas for the years 2006, 2008 and 2010.  The maps could be used to show events with high chlorophyll, both with natural causes (e.g. a Prymnesium polylepis bloom observed in summer 2008) and of anthropogenic causes (e.g. failure in the local sewage treatment plant resulting in a strong spring bloom in 2006). Anomaly maps thereby allow to scan larger coastal stretches to discriminate areas that may require additional sampling by ship, or to identify areas that do not differ much from the median value of the MERIS time series.

Keyword [en]
MERIS, Himmerfjärden, Water quality, Time Series, Chlorophyll, Baltic Sea
National Category
Oceanography, Hydrology, Water Resources
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-123721OAI: oai:DiVA.org:su-123721DiVA: diva2:877464
Projects
EUFP7 Strategic partnership for improved basin-scale water quality parameter retrieval from optical signatures (WaterS) Ref.: 251527FP7 EuRuCAS (project no. 295068); mobility exchange with NIERSCESA/ESRIN contract 21524
Funder
Swedish National Space Board, 165/11Swedish National Space Board, 147/12Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE, 4315403EU, FP7, Seventh Framework Programme, 251527EU, FP7, Seventh Framework Programme, 295068
Available from: 2015-12-07 Created: 2015-12-03 Last updated: 2015-12-18Bibliographically approved
In thesis
1. Remote sensing in optically complex waters: water quality assessment using MERIS data
Open this publication in new window or tab >>Remote sensing in optically complex waters: water quality assessment using MERIS data
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This PhD study focusses on the use of MEdium Resolution Imaging Spectrometer (MERIS) data for reliable and quantitative water-quality assessment of optically-complex waters (lake, brackish and coastal waters). The thesis is divided into two parts: A. intercalibration of reflectance measurements in different optically-complex water bodies (Paper I), and validation of various satellite processing algorithms for the coastal zone (Paper II). B. Applications: the use of MERIS data in integrated coastal zone management mostly using Himmerfjärden bay as an example.

Himmerfjärden bay is one of the most frequently monitored coastal areas in the world and it is also the recipient of a large urban sewage treatment plant, where a number of full-scale nutrient management experiments have been conducted to evaluate the ecological changes due to changes in nutrient schemes in the sewage plant.

Paper I describes the development and assessment of a new hyperspectral handheld radiometer for in situ sampling and validation of remote sensing reflectance.  The instrument is assessed in comparison with readily available radiometers that are commonly used in validation.

Paper II has a focus on the validation of level 2 reflectance and water products derived from MERIS data. It highlights the importance of calibration and validation activities, and the current accuracy and limitations of satellite products in the coastal zone.  Bio-optical in situ data is highlighted as one of the key components for assessing the reliability of current and future satellite missions. Besides suspended particulate matter (SPM), the standard MERIS products have shown to be insufficient to assure data quality retrieval for Baltic Sea waters. Alternative processors and methods such as those assessed and developed in this thesis therefore will have to be put in place in order to secure the success of future operational missions, such as Sentinel-3.

The two presented manuscripts in the applied part B of the thesis (paper III and IV), showed examples on the combined use of in situ measurements with optical remote sensing to support water quality monitoring programs by using turbidity and suspended particulate matter as coastal indicators (manuscript III). The article also provides  a new turbidity algorithm for the Baltic Sea and a robust and cost-efficient method for research and management.  A novel approach to improve the quality of the satellite-derived products in the coastal zone was demonstrated in manuscript IV. The analysis included, the correction for adjacency effects from land and an improved pixel quality screening.  The thesis provides the first detailed spatio-temporal description of the evolution of phytoplankton blooms in Himmerfjärden bay  using quality-assured MERIS data, thus forwarding our understanding of ecological processes in in Swedish coastal waters.

It must be noted that monitoring from space is not a trivial matter in these optically-complex waters dominated by the absorption of coloured dissolved organic matter (CDOM). These types of coastal waters are especially challenging for quantitative assessment from space due to their low reflectance.  Papers III and IV thus also provide tools for a more versatile use in other coastal waters that are not as optically-complex as the highly absorbing Baltic Sea waters. The benefits of the increased spatial-temporal data coverage by optical remote sensing were presented, and also compared to in situ sampling methods (using chlorophyll-a as indicator).

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2015. 58 p.
Keyword
Ocean Colour, MERIS, Baltic Sea, Bio-optics, water quality, Chlorophyll, Turbidity, SPM, Himmerfjärden, Remote Sensing
National Category
Ecology Oceanography, Hydrology, Water Resources
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-123724 (URN)978-91-7649-310-6 (ISBN)
Public defence
2016-01-29, Q211, Department of Ecology, Environment and Plant Sciences, Svante Arrhenius väg 20 A, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish National Space Board, 165/11Swedish National Space Board, 147/12EU, FP7, Seventh Framework Programme, 251527EU, FP7, Seventh Framework Programme, 295068Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE, 4315403Baltic Ecosystem Adaptive Management (BEAM), 4315403
Note

Research funders:

European Space Agency (ESA, contract no.21524/08/I-OL)

NordForsk funding: Nord AquaRemS Ref. no. 80106

NordForsk funding:  NordBaltRemS Ref.no. 42041

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2016-01-05 Created: 2015-12-03 Last updated: 2015-12-22Bibliographically approved

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