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Validation and Evaluation of Global Ocean Satellite Products (Second Edition)

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

Deadline for manuscript submissions: closed (25 April 2025) | Viewed by 6905

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Dr. Po-Chun Hsu

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Center for Space and Remote Sensing Research, National Central University, Taoyuan 32001, Taiwan
Interests: satellite oceanography; ocean dynamics processes and ocean environment; ocean–typhoon interactions; upper ocean and submesoscale processes
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Prof. Dr. Chung-Ru Ho

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Department of Marine Environmental Informatics, National Taiwan Ocean University, Keelung 202301, Taiwan
Interests: remote sensing; physical oceanography; global change; satellite oceanography
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Dr. Shota Katsura

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Atmosphere and Ocean Research Institute, The University of Tokyo, Tokyo 113-8654, Japan
Interests: salinity; mixed layer; water mass
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Dr. Bingqing Liu

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School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA 70503, USA
Interests: ocean color remote sensing; carbon cycling of land–ocean interactions; phytoplankton community dynamics
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Dr. Jen-Ping Peng

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Oceans Graduate School, The University of Western Australia, Crawley, WA 6009, Australia
Interests: physical oceanography; submesoscale frontal dynamics and instabilities; surface boundary layer turbulence and mixing; air–sea interactions; diurnal effects; and upwelling
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Special Issue Information

Dear Colleagues,

Ocean science for sustainable development is one of the important issues of ocean research in this decade. With the development of science and technology, ocean satellite products continue to provide higher spatial resolution and more frequent repeated observations, and geosynchronous satellites can further observe continuous sea surface changes at the same place. Satellite ocean data can effectively observe sea surface variations at various spatial scales in a short period of time, help scientists find new scientific discoveries and clarify various scientific issues, and provide reference materials for scientists to plan before cruise and observation. For this Special Issue, we welcome any papers using ocean satellite products and particularly encourage research examining in situ observation data and breakthrough discoveries in regional and global oceanography.

The topics of interest include, but are not limited to, the following:

Data verification and analysis between in situ observation and ocean satellite products;
Data algorithm and verification of ocean satellite products;
Data comparison and correctness evaluation of various satellite products;
Comparison of numerical simulation and satellite data;
Feedback of climate variability to the ocean;
Breakthrough of scientific issues in regional oceanography.

Dr. Po-Chun Hsu
Prof. Dr. Chung-Ru Ho
Dr. Shota Katsura
Dr. Bingqing Liu
Dr. Jen-Ping Peng
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 submissions that pass pre-check are 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 2700 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

sea surface current, temperature, and salinity
ocean color and chlorophyll-a concentration
oceanic front
new approaches, methods and algorithms
climatic variables
ocean–typhoon interaction
multiscale ocean dynamics

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Related Special Issue

Validation and Evaluation of Global Ocean Satellite Products in Remote Sensing (10 articles)

Published Papers (5 papers)

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Research

31 pages, 14095 KiB

Open AccessArticle

Range and Wave Height Corrections to Account for Ocean Wave Effects in SAR Altimeter Measurements Using Neural Network

by Jiaxue Wang, Maofei Jiang and Ke Xu

Remote Sens. 2025, 17(6), 1031; https://doi.org/10.3390/rs17061031 - 15 Mar 2025

Viewed by 437

Abstract

Compared to conventional pulse-limited altimeters (i.e., low-resolution mode, LRM), the synthetic aperture radar (SAR, i.e., high-resolution mode, HRM) altimeter offers superior precision and along-track resolution abilities. However, because the SAR altimeter relies on Doppler shifts caused by the relative movement between radar scattering points and the altimeter antenna, the geophysical parameters obtained by the SAR altimeter are sensitive to the direction of ocean wave movements driven by the wind and waves. Both practice and theory have shown that the wind and wave effects have a greater impact on HRM data than LRM. LRM values of range and significant wave height (SWH) from modern retracking are the best representations there are of these quantities, and this study aims to bring HRM data into line with them. In this study, wind and wave effects in SAR altimeter measurements were analyzed and corrected. The radar altimeter onboard the Sentinel-6 satellite is the first SAR altimeter to operate in an interleaved open burst mode. It has the capability of simultaneous generation of both LRM and HRM data. This study utilizes Sentinel-6 altimetry data and ERA5 re-analysis data to identify the influence of ocean waves. The analysis is based on the altimeter range and SWH differences between the HRM and LRM measurements with respect to different geophysical parameters derived from model data. Results show that both HRM range and SWH measurements are impacted by SWH and wind speed, and the HRM SWH measurements are also significantly impacted by vertical velocity. An upwave/downwave bias between HRM and LRM range is observed. To reduce wave impact on the SAR altimeter measurements, a back-propagation neural network (BPNN) method is proposed to correct the HRM range and SWH measurements. Based on Sentinel-6 measurements and ERA5 re-analysis data, our corrections significantly reduce biases between LRM and HRM range and SWH values. Finally, the accuracies of the sea surface height (SSH) and SWH measurements after correction are assessed using crossover analysis and compared against NDBC buoy data. The standard deviation (STD) of the HRM SSH differences at crossovers has no significant changes before (3.97 cm) and after (3.94 cm) correction. In comparison to the NDBC data, the root mean square error (RMSE) of the corrected HRM SWH data is 0.187 m, which is significantly better than that with no correction (0.265 m). Full article

(This article belongs to the Special Issue Validation and Evaluation of Global Ocean Satellite Products (Second Edition))

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25 pages, 7245 KiB

Open AccessArticle

Long-Term Evaluation of GCOM-C/SGLI Reflectance and Water Quality Products: Variability Among JAXA G-Portal and JASMES

by Salem Ibrahim Salem, Mitsuhiro Toratani, Hiroto Higa, SeungHyun Son, Eko Siswanto and Joji Ishizaka

Remote Sens. 2025, 17(2), 221; https://doi.org/10.3390/rs17020221 - 9 Jan 2025

Cited by 1 | Viewed by 878

Abstract

The Global Change Observation Mission-Climate (GCOM-C) satellite, launched in December 2017, is equipped with the Second-generation Global Imager (SGLI) sensor, featuring a moderate spatial resolution of 250 m and 19 spectral bands, including the unique 380 nm band. After six years in orbit, [...] Read more.

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) is the primary product for monitoring water quality, forming the basis for deriving key oceanic constituents such as chlorophyll-a (Chla) and total suspended matter (TSM). The Japan Aerospace Exploration Agency (JAXA) provides

R_{r s}

products through two platforms, G-Portal and JASMES, each employing different atmospheric correction methodologies and assumptions. This study aims to evaluate the SGLI full-resolution

R_{r s}

products from G-Portal and JASMES at regional scales (Japan and East Asia) and assess G-Portal

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products globally between January 2018 and December 2023. The evaluation employs in situ matchups from NASA’s Aerosol Robotic Network-Ocean Color (AERONET-OC) and cruise measurements. We also assess the retrieval accuracy of two water quality indices, Chla and TSM. The AERONET-OC data analysis reveals that JASMES systematically underestimates

R_{r s}

values at shorter wavelengths, particularly at 412 nm. While the

R_{r s}

accuracy at 412 nm is relatively low, G-Portal’s

R_{r s}

products perform better than JASMES at shorter wavelengths, showing lower errors and stronger correlations with AERONET-OC data. Both G-Portal and JASMES show lower agreement with AERONET-OC and cruise datasets at shorter wavelengths but demonstrate improved agreement at longer wavelengths (530 nm, 565 nm, and 670 nm). JASMES generates approximately 12% more matchup data points than G-Portal, likely due to G-Portal’s stricter atmospheric correction thresholds that exclude pixels with high reflectance. In situ measurements indicate that G-Portal provides better overall agreement, particularly at lower

R_{r s}

magnitudes and Chla concentrations below 5 mg/m³. This evaluation underscores the complexities and challenges of atmospheric correction, particularly in optically complex coastal waters (Case 2 waters), which may require tailored atmospheric correction methods different from the standard approach. The assessment of temporal consistency and seasonal variations in

R_{r s}

data shows that both platforms effectively capture interannual trends and maintain temporal stability, particularly from the 490 nm band onward, underscoring the potential of SGLI data for long-term monitoring of coastal and oceanic environments. Full article

(This article belongs to the Special Issue Validation and Evaluation of Global Ocean Satellite Products (Second Edition))

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18 pages, 6441 KiB

Open AccessArticle

Evaluation of the Operational Global Ocean Wave Forecasting System of China

by Mengmeng Wu, Juanjuan Wang, Qiongqiong Cai, Yi Wang, Jiuke Wang and Hui Wang

Remote Sens. 2024, 16(18), 3535; https://doi.org/10.3390/rs16183535 - 23 Sep 2024

Viewed by 1228

Abstract

Based on the WAVEWATCH III wave model, China’s National Marine Environmental Forecasting Center has developed an operational global ocean wave forecasting system that covers the Arctic region. In this study, in situ buoy observations and satellite remote sensing data were used to perform a detailed evaluation of the system’s forecasting results for 2022, with a focus on China’s offshore and global ocean waters, so as to comprehensively understand the model’s forecasting performance. The study results showed the following: In China’s coastal waters, the model had a high forecasting accuracy for significant wave heights. The model tended to underestimate the significant wave heights in autumn and winter and overestimate them in spring and summer. In addition, the model slightly underestimated low (below 1 m) wave heights, while overestimating them in other ranges. In terms of spatial distribution, negative deviations and high scatter indexes were observed in the forecasting of significant wave heights in semi-enclosed sea areas such as the Bohai Sea, Yellow Sea, and Beibu Gulf, with the largest negative deviation occurring near Liaodong Bay of the Bohai Sea (−0.18 m). There was a slight positive deviation (0.01 m) in the East China Sea, while the South China Sea exhibited a more significant positive deviation (0.17 m). The model showed a trend of underestimation for the forecasting of the mean wave period in China’s coastal waters. In the global oceanic waters, the forecasting results of the model were found to have obvious positive deviations for most regions, with negative deviations mainly occurring on the east coast and in relatively closed basins. There were latitude differences in the forecasting deviations of the model: specifically, the most significant positive deviations occurred in the Southern Ocean, with smaller positive deviations toward the north, while a slight negative deviation was observed in the Arctic waters. Overall, the global wave model has high reliability and can meet the current operational forecasting needs. In the future, the accuracy and performance of ocean wave forecasting can be further improved by adjusting the parameterization scheme, replacing the wind fields with more accurate ones, adopting spherical multiple-cell grids, and data assimilation. Full article

(This article belongs to the Special Issue Validation and Evaluation of Global Ocean Satellite Products (Second Edition))

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22 pages, 7667 KiB

Open AccessArticle

Altimeter Calibrations in the Preliminary Four Years’ Operation of Wanshan Calibration Site

by Wanlin Zhai, Jianhua Zhu, Hailong Peng, Chuntao Chen, Longhao Yan, He Wang, Xiaoqi Huang, Wu Zhou, Hai Guo and Yufei Zhang

Remote Sens. 2024, 16(6), 1087; https://doi.org/10.3390/rs16061087 - 20 Mar 2024

Viewed by 1460

Abstract

In order to accomplish the calibration and validation (Cal/Val) of altimeters, the Wanshan calibration site (WSCS) has been used as a calibration site for satellite altimeters since its completion in August 2019. In this paper, we introduced the WSCS and the dedicated equipment including permanent GNSS reference stations (PGSs), acoustic tide gauges (ATGs), and dedicated GNSS buoys (DGB), etc. placed on Zhi’wan, Wai’ling’ding, Dan’gan, and Miao’Wan islands of the WSCS. The PGSs data of Zhi’wan and Wai’ling’ding islands were processed and analyzed using the GAMIT/GLOBK (Version 10.7) and Hector (Version 1.9) software to define the datum for Cal/Val of altimeters in WSCS. The DGB was used to transfer the datum from the PGSs to the ATGs of Zhi’wan, Wai’ling’ding, and Dan’gan islands. Separately, the tidal and mean sea surface (MSS) corrections are needed in the Cal/Val of altimeters. We evaluated the global/regional tide models of FES2014, HAMTIDE12, DTU16, NAO99jb, GOT4.10, and EOT20 using the three in situ tide gauge data of WSCS and Hong Kong tide gauge data (No. B329) derived from the Global Sea Level Observing System. The HAMTIDE12 tide model was chosen to be the most accurate one to maintain the tidal difference between the locations of the ATGs and the altimeter footprints. To establish the sea surface connections between the ATGs and the altimeter footprints, a GPS towing body and a highly accurate ship-based SSH measurement system (HASMS) were used to measure the sea surface of this area in 2018 and 2022, respectively. The global/regional mean sea surface (MSS) models of DTU 2021, EGM 2008 (mean dynamic topography minus by CLS_MDT_2018), and CLS2015 were accurately evaluated using the in situ measured data and HY-2A altimeter, and the CLS2015 MSS model was used for Cal/Val of altimeters in WSCS. The data collected by the equipment of WSCS, related auxiliary models mentioned above, and the sea level data of the hydrological station placed on Dan’gan island were used to accomplish the Cal/Val of HY-2B, HY-2C, Jason-3, and Sentinel-3A (S3A) altimeters. The bias of HY-2B (Pass No. 375) was −16.7 ± 45.2 mm, with a drift of 0.5 mm/year. The HY-2C biases were −18.9 ± 48.0 mm with drifts of 0.0 mm/year and −5.6 ± 49.3 mm with −0.3 mm/year drifts for Pass No. 170 and 185, respectively. The Jason-3 bias was −4.1 ± 78.7 mm for Pass No. 153 and −25.8 ± 85.5 mm for Pass No. 012 after it has changed its orbits since April 2022, respectively. The biases of S3A were determined to be −16.5 ± 46.3 mm with a drift of −0.6 mm/year and −9.8 ± 30.1 mm with a drift of 0.5 mm/year for Pass No. 260 and 309, respectively. The calibration results show that the WSCS can commercialize the satellite altimeter calibration. We also discussed the calibration potential for a wide swath satellite altimeter of WSCS. Full article

(This article belongs to the Special Issue Validation and Evaluation of Global Ocean Satellite Products (Second Edition))

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20 pages, 9099 KiB

Open AccessArticle

Accuracy Evaluation of Ocean Wave Spectra from Sentinel-1 SAR Based on Buoy Observations and ERA5 Data

by Fengjia Sun, Jungang Yang and Wei Cui

Remote Sens. 2024, 16(6), 987; https://doi.org/10.3390/rs16060987 - 12 Mar 2024

Cited by 2 | Viewed by 2076

Abstract

Doppler mis-registrations in azimuth can lead to ocean waves shorter than a specific wavelength being undetectable by SAR. In order to evaluate the actual ocean wave observation ability, the accuracy of Sentinel-1 SAR ocean wave spectra from January 2016 to December 2021 is evaluated by comparisons to NDBC buoys, ERA5 wave height, and CMEMS buoys. The results compared with NDBC show that the spectral shape of Sentinel-1 SAR ocean wave spectra is accurate, while the spectral values need to be improved. The wave spectra of Sentinel-1 have the best observations in season autumn. The comparison results of total wave height show the RMSE and bias are 0.91 m and −0.52 m for the comparisons to NDBC buoy wave spectra data, 0.93 m and −0.68 m for the comparison to ERA5 wave height data, and 0.9 m and −0.35 m for the comparisons to CMEMS buoy data. The comparison results of wave height in different wind speeds and areas shows that the accuracy of Sentinel-1 wave mode data is relatively good in the open ocean located in middle and low latitude area under the medium wind speed, while those are relatively poor in high latitude areas or the areas with excessively high or low wind speed. Full article

(This article belongs to the Special Issue Validation and Evaluation of Global Ocean Satellite Products (Second Edition))

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