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Remote sensing in optically complex waters: water quality assessment using MERIS data
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. (Marine ecology)ORCID iD: 0000-0003-3777-6788
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 [en]
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: urn:nbn:se:su:diva-123724ISBN: 978-91-7649-310-6 (print)OAI: oai:DiVA.org:su-123724DiVA: diva2:885233
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: 2017-04-11Bibliographically approved
List of papers
1. Intercomparison in the field between the new WISP-3 and other radiometers (TriOS Ramses, ASD FieldSpec, and TACCS)
Open this publication in new window or tab >>Intercomparison in the field between the new WISP-3 and other radiometers (TriOS Ramses, ASD FieldSpec, and TACCS)
Show others...
2012 (English)In: Journal of Applied Remote Sensing, ISSN 1931-3195, E-ISSN 1931-3195, Vol. 6, 063615Article in journal (Refereed) Published
Abstract [en]

Optical close-range instruments can be applied to derive water quality parameters for monitoring purposes and for validation of optical satellite data. In situ radiometers are often difficult to deploy, especially from a small boat or a remote location. The water insight spectrometer (WISP-3) is a new hand-held radiometer for monitoring water quality, which automatically performs measurements with three radiometers (L-sky, L-u, E-d) and does not need to be connected with cables and electrical power during measurements. The instrument is described and its performance is assessed by an intercomparison to well-known radiometers, under real fieldwork conditions using a small boat and with sometimes windy and cloudy weather. Root mean squared percentage errors relative to those of the TriOS system were generally between 20% and 30% for remote sensing reflection, which was comparable to those of the other instruments included in this study. From this assessment, it can be stated that for the tested conditions, the WISP-3 can be used to obtain reflection spectra with accuracies in the same range as well-known instruments. When tuned with suitable regional algorithms, it can be used for quick scans for water quality monitoring of Chl, SPM, and aCDOM.

Keyword
WISP-3, radiometer, intercomparison, reflectance
National Category
Environmental Sciences Remote Sensing
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-88750 (URN)10.1117/1.JRS.6.063615 (DOI)000315260200001 ()
Funder
EU, FP7, Seventh Framework Programme
Note

AuthorCount:11;

Available from: 2013-03-26 Created: 2013-03-26 Last updated: 2017-12-06Bibliographically approved
2. Evaluation of MERIS products from Baltic Sea coastal waters rich in CDOM
Open this publication in new window or tab >>Evaluation of MERIS products from Baltic Sea coastal waters rich in CDOM
2014 (English)In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 10, no 3, 377-396 p.Article in journal (Refereed) Published
Abstract [en]

In this study, retrievals of the medium resolution imaging spectrometer (MERIS) reflectances and water quality products using four different coastal processing algorithms freely available are assessed by comparison against sea-truthing data. The study is based on a pair-wise comparison using processor-dependent quality flags for the retrieval of valid common macro-pixels. This assessment is required in order to ensure the reliability of monitoring systems based on MERIS data, such as the Swedish coastal and lake monitoring system (http://vattenkvalitet.se). The results show that the pre-processing with the Improved Contrast between Ocean and Land (ICOL) processor, correcting for adjacency effects, improves the retrieval of spectral reflectance for all processors. Therefore, it is recommended that the ICOL processor should be applied when Baltic coastal waters are investigated. Chlorophyll was retrieved best using the FUB (Free University of Berlin) processing algorithm, although overestimations in the range 18-26.5 %, dependent on the compared pairs, were obtained. At low chlorophyll concentrations (< 2.5 mg m(-3)), data dispersion dominated in the retrievals with the MEGS (MERIS ground segment processor) processor. The lowest bias and data dispersion were obtained with MEGS for suspended particulate matter, for which overestimations in the range of 8-16% were found. Only the FUB retrieved CDOM (coloured dissolved organic matter) correlate with in situ values. However, a large systematic underestimation appears in the estimates that nevertheless may be corrected for by using a local correction factor. The MEGS has the potential to be used as an operational processing algorithm for the Himmerfjarden bay and adjacent areas, but it requires further improvement of the atmospheric correction for the blue bands and better definition at relatively low chlorophyll concentrations in the presence of high CDOM attenuation.

National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-106536 (URN)10.5194/os-10-377-2014 (DOI)000338651700006 ()
Note

AuthorCount:3;

Available from: 2014-08-11 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved
3. Retrieval of suspended pariculate matter from MERIS data: Algorithm development and validation
Open this publication in new window or tab >>Retrieval of suspended pariculate matter from MERIS data: Algorithm development and validation
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-141668 (URN)
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-04-11Bibliographically approved
4. Using MERIS data to assess the spatial and temporal variability of phytoplankton in coastal areas
Open this publication in new window or tab >>Using MERIS data to assess the spatial and temporal variability of phytoplankton in coastal areas
2017 (English)In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 38, no 7, 2004-2028 p.Article in journal (Refereed) Published
Abstract [en]

This study aims to highlight how satellite data can be used for an improved understanding of ecological processes in a narrow coastal bay. The usefulness of the Medium Resolution Imaging Spectrometer (MERIS) data (2003-2011) as a complement to the in situ monitoring in Himmerferdenn (HF) bay is used as an example that can also be applied to other coastal areas. HF 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. MERIS data was used for the integration of chlorophyll-a (chl-a) over each waterbody in the HF area, following the national waterbody classification by the Swedish Meteorological and Hydrological Institute (SMHI). Chl-a anomaly maps were produced for the bay and its adjacent areas. The maps could be used to show events with high chl-a, 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.

National Category
Oceanography, Hydrology, Water Resources
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-141265 (URN)10.1080/01431161.2016.1249307 (DOI)000394652900013 ()
Available from: 2017-04-07 Created: 2017-04-07 Last updated: 2017-11-29Bibliographically approved

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