11:15 AM - 11:30 AM
[AOS18-03] Calculation for Lowest Astronomical Tide using GNSS observation data of Autonomous Ocean Vehicle (AOV) in the waters
Keywords:GNSS, tide level, tidal observation, ellipsoid
The Autonomous Ocean Vehicle (AOV) is an unmanned observation platform that moves autonomously using the vertical movement of waves as a power source. It is equipped with multiple observation instruments to observe meteorological and oceanographic phenomena. The AOV is equipped with a GNSS measurement device, and by observing the tide level from the vertical movement of the antenna, it is possible to observe tidal levels around remote islands and natural coasts facing the open ocean where it is difficult to install tide gauges. In addition, AOVs are powered by solar power, so they can be operated at sea for long periods of time. The Japan Coast Guard’s Hydrographic and Oceanographic Department has been conducting tidal observations using AOVs mainly in the waters of Western Japan since 2016. In tidal observations, the Lowest Astronomical Tide (LAT) is obtained and the ellipsoid height of the LAT is calculated. In this presentation, we report on the calculation method of LAT using GNSS observation data from AOVs and its accuracy evaluation.
GNSS observations using AOVs were conducted in the waters around the Oki Islands from 2017 to 2022. First, GNSS observation data was subjected to PPP-AR analysis, and float solutions were removed and smoothed to obtain hourly tide data. To evaluate the accuracy of the hourly tide data, the tide data from the Saigo tide station, which is located in the Dogo area of the Oki Islands in Shimane Prefecture and is under the jurisdiction of the Japan Meteorological Agency, was used as the reference tide level, and outliers were removed. Finally, harmonic constants were calculated to estimate the tide level for 19 years, and the lowest tide level was set as the LAT to obtain the ellipsoid height of the LAT.
To evaluate the accuracy of the calculation method, the ellipsoid height of the LAT was calculated from the tide data from Saigo tide station and compared with the AOV data. As a result, a difference of 0.19 m occurred. To examine the validity of the difference, the geoid height of the center of the AOV observation area and the Saigo tide station was obtained using “the Geoid 2024 Japan and its Surroundings” (trial version) created by the Geospatial Information Authority of Japan. The difference in geoid height between the two points is 0.22 m, and the difference in the ellipsoid height of the LAT is thought to be due to the difference in geoid height. These results show that the LAT calculation method is valid.
GNSS observations using AOVs were conducted in the waters around the Oki Islands from 2017 to 2022. First, GNSS observation data was subjected to PPP-AR analysis, and float solutions were removed and smoothed to obtain hourly tide data. To evaluate the accuracy of the hourly tide data, the tide data from the Saigo tide station, which is located in the Dogo area of the Oki Islands in Shimane Prefecture and is under the jurisdiction of the Japan Meteorological Agency, was used as the reference tide level, and outliers were removed. Finally, harmonic constants were calculated to estimate the tide level for 19 years, and the lowest tide level was set as the LAT to obtain the ellipsoid height of the LAT.
To evaluate the accuracy of the calculation method, the ellipsoid height of the LAT was calculated from the tide data from Saigo tide station and compared with the AOV data. As a result, a difference of 0.19 m occurred. To examine the validity of the difference, the geoid height of the center of the AOV observation area and the Saigo tide station was obtained using “the Geoid 2024 Japan and its Surroundings” (trial version) created by the Geospatial Information Authority of Japan. The difference in geoid height between the two points is 0.22 m, and the difference in the ellipsoid height of the LAT is thought to be due to the difference in geoid height. These results show that the LAT calculation method is valid.