Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan
Changes in sea surface salinity (SSS) caused by the discharge of freshwater plumes from rivers affect the marine environment in estuaries; therefore, monitoring SSS is essential for understanding the changes in physical phenomena within coastal ecosystems induced by river plume discharge. Previous s...
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MDPI AG
2023-06-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/15/12/3088 |
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| author | Yu Toguchi Satoshi Fujii |
| author_facet | Yu Toguchi Satoshi Fujii |
| author_sort | Yu Toguchi |
| collection | DOAJ |
| description | Changes in sea surface salinity (SSS) caused by the discharge of freshwater plumes from rivers affect the marine environment in estuaries; therefore, monitoring SSS is essential for understanding the changes in physical phenomena within coastal ecosystems induced by river plume discharge. Previous studies showed that salinity could be estimated using a very-high-frequency radar; however, this method was only validated over a short period and few qualitative evaluations were performed. Therefore, to verify quantitative assessments of SSS estimates for practical use, we estimated SSS using the Doppler spectrum of a 24.5-MHz phased-array high-frequency (HF) radar installed in Ise Bay, Japan, and data of approximately 1 year were used for verification. The radar-estimated SSS map was consistent with the velocity field and salinity distribution reported in previous studies. The root mean square error (RMSE) of the SSS estimate for 1-h radar data compared with in situ observations was 4.42 psu when the effect of wind on the received power was removed and 5.04 psu when it was not. For the daily (25-h) average, the RMSE when the effect of wind was considered was 3.32 psu. These results were considered sufficiently applicable in closed coastal areas such as Ise Bay, where the SSS decreases rapidly by 10 psu or more due to river flooding. The results revealed that the HF radar, which can continuously measure sea surface velocity and SSS with a high spatiotemporal resolution, can be a useful tool for providing a deeper understanding of the physical and environmental phenomena that are greatly affected by river water discharge. |
| first_indexed | 2024-03-11T01:59:27Z |
| format | Article |
| id | doaj.art-ef5ce653dea94096a9a20e3f48790219 |
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| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-11T01:59:27Z |
| publishDate | 2023-06-01 |
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| spelling | doaj.art-ef5ce653dea94096a9a20e3f487902192023-11-18T12:26:14ZengMDPI AGRemote Sensing2072-42922023-06-011512308810.3390/rs15123088Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, JapanYu Toguchi0Satoshi Fujii1Graduate School of Engineering and Science, University of the Ryukyus, 1 Senbaru, Nishihara 903-0213, Okinawa, JapanFaculty of Engineering, University of the Ryukyus, 1 Senbaru, Nishihara 903-0213, Okinawa, JapanChanges in sea surface salinity (SSS) caused by the discharge of freshwater plumes from rivers affect the marine environment in estuaries; therefore, monitoring SSS is essential for understanding the changes in physical phenomena within coastal ecosystems induced by river plume discharge. Previous studies showed that salinity could be estimated using a very-high-frequency radar; however, this method was only validated over a short period and few qualitative evaluations were performed. Therefore, to verify quantitative assessments of SSS estimates for practical use, we estimated SSS using the Doppler spectrum of a 24.5-MHz phased-array high-frequency (HF) radar installed in Ise Bay, Japan, and data of approximately 1 year were used for verification. The radar-estimated SSS map was consistent with the velocity field and salinity distribution reported in previous studies. The root mean square error (RMSE) of the SSS estimate for 1-h radar data compared with in situ observations was 4.42 psu when the effect of wind on the received power was removed and 5.04 psu when it was not. For the daily (25-h) average, the RMSE when the effect of wind was considered was 3.32 psu. These results were considered sufficiently applicable in closed coastal areas such as Ise Bay, where the SSS decreases rapidly by 10 psu or more due to river flooding. The results revealed that the HF radar, which can continuously measure sea surface velocity and SSS with a high spatiotemporal resolution, can be a useful tool for providing a deeper understanding of the physical and environmental phenomena that are greatly affected by river water discharge.https://www.mdpi.com/2072-4292/15/12/3088high-frequency radarwave spectrasea surface salinityelectric conductivityJONSWAP spectrum |
| spellingShingle | Yu Toguchi Satoshi Fujii Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan Remote Sensing high-frequency radar wave spectra sea surface salinity electric conductivity JONSWAP spectrum |
| title | Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan |
| title_full | Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan |
| title_fullStr | Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan |
| title_full_unstemmed | Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan |
| title_short | Quantitative Assessment of Sea Surface Salinity Estimates Using a High-Frequency Radar in Ise Bay, Japan |
| title_sort | quantitative assessment of sea surface salinity estimates using a high frequency radar in ise bay japan |
| topic | high-frequency radar wave spectra sea surface salinity electric conductivity JONSWAP spectrum |
| url | https://www.mdpi.com/2072-4292/15/12/3088 |
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