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Special Issue "Fiducial Reference Measurements for Satellite Ocean Colour"

A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Ocean Remote Sensing".

Deadline for manuscript submissions: closed (30 April 2019)

Special Issue Editors

Guest Editor
Dr. Andrew Clive Banks

Institute of Oceanography, Hellenic Centre for Marine Research, Former US Base Gournes, 71500 Hersonissos, Crete, Greece
Website | E-Mail
Interests: Earth observation; satellite oceanography (biological and physical); ocean colour; marine optics; radiative transfer modelling; climate change; processing, validation and vicarious calibration of satellite data; accuracy of satellite and in situ data (uncertainty and SI traceability); fiducial reference measurements; essential climate variables; open ocean and coastal remote sensing of the Hellenic Seas and Eastern Mediterranean
Guest Editor
Dr. Christophe Lerebourg

ACRI-ST, 260 Route du Pin Montard, BP 234, 06904 Sophia-Antipolis, France
Website | E-Mail
Interests: signal processing; optics and lasers; data acquisition; calibration; aerosols; uncertainty analysis; optical metrology
Guest Editor
Dr. Kevin Ruddick

Royal Belgian Institute for Natural Sciences (RBINS), 100 Gelledelle, 1200 Brussels, Belgium
Website | E-Mail
Guest Editor
Dr. Gavin Tilstone

Plymouth Marine Laboratory (PML), Prospect Place, Plymouth PL1 3DH, UK
Website | E-Mail
Interests: optics; photosynthesis; primary production; phytoplankton biology; remote sensing
Guest Editor
Dr. Riho Vendt

Tartu Observatory (TO), University of Tartu, Observatooriumi 1, EE-61602 Tõravere, Estonia
Website | E-Mail
Interests: Metrology, calibration and testing; SI traceability and uncertainty evaluation; characterization of measurement instruments; quality assurance; data validation; accuracy of in situ data; fiducial reference measurements; design of intercomparison measurements and analysis of comparison data; optical radiometry; thermometry, thermal effects and modelling; Earth observation; space technology

Special Issue Information

Dear Colleagues,

Fiducial Reference Measurements (FRM) are a suite of independent ground measurements that provide the maximum return on investment for a satellite mission by delivering to users the required confidence in data products, in the form of independent validation results and satellite measurement uncertainty estimation, over the entire end-to-end duration of a satellite mission. The FRM must have documented traceability to the SI units (in terms of an unbroken chain of calibrations and comparisons), be independent from the satellite retrieval process, have evaluated uncertainty budgets for all FRM instruments and measurement procedures applied, have defined and adhered-to protocols and community-wide management practices, and be openly available for independent scrutiny.

Within this context, the European Space Agency (ESA) has funded a series of projects targeting the validation of satellite data products (e.g., for altimetry, atmosphere, land, and ocean) and setting up the framework, standards, and protocols for future satellite validation efforts. The FRM4SOC project has been structured to provide support for evaluating and improving the state of the art in Ocean Colour Radiometry (OCR) through a series of comparisons under the auspices of the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration & Validation and in support of the CEOS ocean colour virtual constellation. The methods of OCR give us valuable information on the management of the marine ecosystem, the role of the ocean ecosystem in climate change, aquaculture, fisheries, coastal zone water quality, and the mapping and monitoring of harmful algal blooms. This is how the FRM4SOC project makes a fundamental contribution to the European system for monitoring the Earth (Copernicus).

The objectives of the FRM4SOC, in particular, are to establish and maintain SI-traceable ground-based FRM for satellite OCR with the relevant protocols and uncertainty budgets for an ongoing international reference measurement system supporting the validation of satellite ocean colour. This is in support of ensuring the high quality and accuracy of Copernicus satellite mission data, in particular the Sentinel-2 MSI and Sentinel-3 OLCI ocean colour products.

The final workshop of the FRM4SOC project will take place at the National Physical Laboratory of the UK on October 4–5, 2018 (see https://frm4soc.org/index.php/activities/final_workshop/ ). This workshop has the title of "The Fiducial Reference Measurement Network for Satellite Ocean Colour" and the objective of forming an ocean colour community consensus-driven scientific roadmap for the future of satellite ocean colour validation.

In addition to the papers resultant from the FRM4SOC project and workshop, we invite the remote sensing community to submit papers on this presently “hot” topic in earth observation. Anything relevant to working towards fiducial reference measurements for satellite ocean colour validation or vicarious calibration will be accepted, for example on the following topics covered in the FRM4SOC workshop:

  • Ocean Colour Radiometry (OCR) calibration source inter-comparisons;
  • Laboratory-based OCR inter-comparisons;
  • Field-based OCR inter-comparisons;
  • SI traceability and end-to-end uncertainty budgets–from calibration to field measurements;
  • Improvements in ocean colour radiometers, their calibration, and characterisation;
  • Measurement requirements and protocols when operating FRM OCR for satellite validation
  • Satellite ocean colour validation measurements and their uncertainties;
  • FRM in the context of ocean colour system vicarious calibration;

Dr. Andrew Clive Banks
Dr. Christophe Lerebourg
Dr. Kevin Ruddick
Dr. Gavin Tilstone
Dr. Riho Vendt
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • satellite ocean colour
  • fiducial reference measurements (FRM)
  • calibration and validation
  • SI traceability and uncertainty
  • Copernicus
  • European Space Agency (ESA)
  • CEOS

Published Papers (4 papers)

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Research

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Open AccessArticle
The Pan-and-Tilt Hyperspectral Radiometer System (PANTHYR) for Autonomous Satellite Validation Measurements—Prototype Design and Testing
Remote Sens. 2019, 11(11), 1360; https://doi.org/10.3390/rs11111360
Received: 17 May 2019 / Accepted: 3 June 2019 / Published: 6 June 2019
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Abstract
This paper describes a system, named “pan-and-tilt hyperspectral radiometer system” (PANTHYR) that is designed for autonomous measurement of hyperspectral water reflectance. The system is suitable for deployment in diverse locations (including offshore platforms) for the validation of water reflectance derived from any satellite [...] Read more.
This paper describes a system, named “pan-and-tilt hyperspectral radiometer system” (PANTHYR) that is designed for autonomous measurement of hyperspectral water reflectance. The system is suitable for deployment in diverse locations (including offshore platforms) for the validation of water reflectance derived from any satellite mission with visible and/or near-infrared spectral bands (400–900 nm). Key user requirements include reliable autonomous operation at remote sites without grid power or cabled internet and only limited maintenance (1–2 times per year), flexible zenith and azimuth pointing, modularity to adapt to future evolution of components and different sites (power, data transmission, and mounting possibilities), and moderate hardware acquisition cost. PANTHYR consists of two commercial off-the-shelf (COTS) hyperspectral radiometers, mounted on a COTS pan-and-tilt pointing system, controlled by a single-board-computer and associated custom-designed electronics which provide power, pointing instructions, and data archiving and transmission. The variable zenith pointing improves protection of sensors which are parked downward when not measuring, and it allows for use of a single radiance sensor for both sky and water viewing. The latter gives cost reduction for radiometer purchase, as well as reduction of uncertainties associated with radiometer spectral and radiometric differences for comparable two-radiance-sensor systems. The system is designed so that hardware and software upgrades or changes are easy to implement. In this paper, the system design requirements and choices are described, including details of the electronics, hardware, and software. A prototype test on the Acqua Alta Oceanographic Tower (near Venice, Italy) is described, including comparison of the PANTHYR system data with two other established systems: the multispectral autonomous AERONET-OC data and a manually deployed three-sensor hyperspectral system. The test established that high-quality hyperspectral data for water reflectance can be acquired autonomously with this system. Lessons learned from the prototype testing are described, and the future perspectives for the hardware and software development are outlined. Full article
(This article belongs to the Special Issue Fiducial Reference Measurements for Satellite Ocean Colour)
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Open AccessArticle
Field Intercomparison of Radiometers Used for Satellite Validation in the 400–900 nm Range
Remote Sens. 2019, 11(9), 1129; https://doi.org/10.3390/rs11091129
Received: 26 March 2019 / Revised: 24 April 2019 / Accepted: 8 May 2019 / Published: 11 May 2019
Cited by 1 | PDF Full-text (6381 KB) | HTML Full-text | XML Full-text
Abstract
An intercomparison of radiance and irradiance ocean color radiometers (the second laboratory comparison exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted [...] Read more.
An intercomparison of radiance and irradiance ocean color radiometers (the second laboratory comparison exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: (1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; (2) indoor, laboratory intercomparison using stable radiance and irradiance sources in a controlled environment; (3) outdoor, field intercomparison of natural radiation sources over a natural water surface. The aim of the experiment was to provide a link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the third phase of LCE-2: The results of the field experiment. The calibration of radiometers and laboratory comparison experiment are presented in a related paper of the same journal issue. Compared to the laboratory comparison, the field intercomparison has demonstrated substantially larger variability between freshly calibrated sensors, because the targets and environmental conditions during radiometric calibration were different, both spectrally and spatially. Major differences were found for radiance sensors measuring a sunlit water target at viewing zenith angle of 139° because of the different fields of view. Major differences were found for irradiance sensors because of imperfect cosine response of diffusers. Variability between individual radiometers did depend significantly also on the type of the sensor and on the specific measurement target. Uniform SI traceable radiometric calibration ensuring fairly good consistency for indoor, laboratory measurements is insufficient for outdoor, field measurements, mainly due to the different angular variability of illumination. More stringent specifications and individual testing of radiometers for all relevant systematic effects (temperature, nonlinearity, spectral stray light, etc.) are needed to reduce biases between instruments and better quantify measurement uncertainties. Full article
(This article belongs to the Special Issue Fiducial Reference Measurements for Satellite Ocean Colour)
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Open AccessArticle
Laboratory Intercomparison of Radiometers Used for Satellite Validation in the 400–900 nm Range
Remote Sens. 2019, 11(9), 1101; https://doi.org/10.3390/rs11091101
Received: 25 March 2019 / Revised: 2 May 2019 / Accepted: 5 May 2019 / Published: 8 May 2019
Cited by 2 | PDF Full-text (6981 KB) | HTML Full-text | XML Full-text
Abstract
An intercomparison of radiance and irradiance ocean color radiometers (The Second Laboratory Comparison Exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted [...] Read more.
An intercomparison of radiance and irradiance ocean color radiometers (The Second Laboratory Comparison Exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: 1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; 2) Indoor intercomparison using stable radiance and irradiance sources in controlled environment; and 3) Outdoor intercomparison of natural radiation sources over terrestrial water surface. The aim of the experiment was to provide one link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the activities and results of the first two phases of LCE-2: the SI-traceable radiometric calibration and indoor intercomparison, the results of outdoor experiment are presented in a related paper of the same journal issue. The indoor experiment of the LCE-2 has proven that uniform calibration just before the use of radiometers is highly effective. Distinct radiometers from different manufacturers operated by different scientists can yield quite close radiance and irradiance results (standard deviation s < 1%) under defined conditions. This holds when measuring stable lamp-based targets under stationary laboratory conditions with all the radiometers uniformly calibrated against the same standards just prior to the experiment. In addition, some unification of measurement and data processing must be settled. Uncertainty of radiance and irradiance measurement under these conditions largely consists of the sensor’s calibration uncertainty and of the spread of results obtained by individual sensors measuring the same object. Full article
(This article belongs to the Special Issue Fiducial Reference Measurements for Satellite Ocean Colour)
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Other

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Open AccessLetter
Filling the Gaps of Missing Data in the Merged VIIRS SNPP/NOAA-20 Ocean Color Product Using the DINEOF Method
Remote Sens. 2019, 11(2), 178; https://doi.org/10.3390/rs11020178
Received: 18 December 2018 / Revised: 15 January 2019 / Accepted: 16 January 2019 / Published: 18 January 2019
Cited by 2 | PDF Full-text (4929 KB) | HTML Full-text | XML Full-text
Abstract
The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) and National Oceanic and Atmospheric Administration (NOAA)-20 has been providing a large amount of global ocean color data, which are critical for monitoring and understanding of ocean optical, biological, [...] Read more.
The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) and National Oceanic and Atmospheric Administration (NOAA)-20 has been providing a large amount of global ocean color data, which are critical for monitoring and understanding of ocean optical, biological, and ecological processes and phenomena. However, VIIRS-derived daily ocean color images on either SNPP or NOAA-20 have some limitations in ocean coverage due to its swath width, high sensor-zenith angle, high sun glint, and cloud, etc. Merging VIIRS ocean color products derived from the SNPP and NOAA-20 significantly increases the spatial coverage of daily images. The two VIIRS sensors on the SNPP and NOAA-20 have similar sensor characteristics, and global ocean color products are generated using the same Multi-Sensor Level-1 to Level-2 (MSL12) ocean color data processing system. Therefore, the merged VIIRS ocean color data from the two sensors have high data quality with consistent statistical property and accuracy globally. Merging VIIRS SNPP and NOAA-20 ocean color data almost removes the gaps of missing pixels due to high sensor-zenith angles and high sun glint contamination, and also significantly reduces the gaps due to cloud cover. However, there are still gaps of missing pixels in the merged ocean color data. In this study, the Data Interpolating Empirical Orthogonal Functions (DINEOF) are applied on the merged VIIRS SNPP/NOAA-20 global Level-3 ocean color data to completely reconstruct the missing pixels. Specifically, DINEOF is applied to 30 days of daily merged global Level-3 chlorophyll-a (Chl-a) data of 9-km spatial resolution from 19 June to 18 July 2018. To quantitatively evaluate the accuracy of the DINEOF reconstructed data, a set of valid pixels are intentionally treated as “missing pixels”, so that reconstructed data can be compared with the original data. Results show that mean ratios of the reconstructed/original are 1.012, 1.012, 1.015, and 0.997 for global ocean, oligotrophic waters, deep waters, and coastal and inland waters, respectively. The corresponding standard deviation (SD) of the ratios are 0.200, 0.164, 0.182, and 0.287, respectively. Gap-filled daily Chl-a images reveal many large-scale and meso-scale ocean features that are invisible in the original SNPP or NOAA-20 Chl-a images. It is also demonstrated that the gap-filled data based on the merged products show more details in the dynamic ocean features than those based on SNPP or NOAA-20 alone. Full article
(This article belongs to the Special Issue Fiducial Reference Measurements for Satellite Ocean Colour)
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