5:15 PM - 7:15 PM
[AOS18-P03] Assessment of SST Measurements at Different Water Depths Using Unmanned Surface Vehicles and Drifting Buoys
Keywords:Sea Surface Temperature (SST), Wave glider, Himawari-9
As seawater temperature rises due to global warming, it is necessary to understand the interaction between the atmosphere and the ocean in order to promote understanding of climate change. In situ observations in the ocean play an important role. We analyzed in situ observations on sea surface temperature (SST) at different depths using an unmanned surface vehicle (USV) equipped with an SST sensor and a drifting buoy, and then compared the results with satellite retrieved data.
In situ observation data are acquired using two wave gliders (WGs) (SV2 and SV3) provided by Liquid Robotics, Inc., which have experienced typhoon observations [1]. A WG is composed of a sea surface float, a submerged glider and a connecting cable and equipped with a suite of customizable sensors for SSTs. A conductivity-temperature-depth sensor (CTD: Sea-Bird Scientific) installed on the glider. The length of the cable varies depending on the type of WG; SV2 at 6.5m and SV3 at 8.5m. An acoustic doppler current profiler (ADCP: Teledyne Marine, Workhorse ADCP) is mainly used to measure currents, but can also measure seawater temperature, and installed on the bottom of the float. As the WG measures SSTs at multiple water depths, we will analyze the diurnal variations caused by solar radiation across these depths (Fig.1). The weather from Aug. 8 to 15 in 2024 was mostly sunny, leading to large daily fluctuations in SSTs. After that, the weather turned to rainy and cloudy conditions, and typhoon ‘JONGDARI’ developed near the observation point on Aug. 19. SSTs had dropped by approximately 1°C. In addition to using the WG, we conducted SST observations with two drifting buoys (Buoy1 and Buoy2) at a water depth of nearly 0 m. SSTs measurements from the ADCP and drifting buoys represent SST_subskin, while the CTD data from the WGs represent SST_depth: SST_6.5m for SV2 and SST_8.5m for SV3, which classifies several types of SSTs at different seawater depths [2]. The SST measurable by satellite remote sensing varies depending on the wavelength and frequency of the electromagnetic waves [2]. SST_skin is primarily measured using infrared satellite sensors, which capture data at a depth of approximately 10-20 μm. On the other hand, SST_subskin is measured using microwave radiometers operating in the 6-11 GHz frequency range, at depths less than 1 m. SST_depth refers to the temperature at a specific water depth that cannot be measured using satellite-based remote sensing due to the absorption and emission characteristics of radiation within the ocean's surface layer. Fig.2 shows comparison of SSTs measured by buoys with satellite named Himawari-9 [3] using infrared sensor. While the satellite measures and retrieves SSTs at shallower depths compared to buoys, the daily patterns of seawater temperature fluctuations caused by solar radiation show good agreement between the two.
In this experiment, we observed variations in SST values among sensors installed at different depths. Since the sensor types and their performance differ, we plan to conduct comparative evaluations at multiple depths using identical sensors in future. Additionally, a comparison of SSTs measured by the buoys and satellite demonstrated that SSTs are warmed by solar radiation, with daily fluctuation patterns showing strong similarity. We aim to compare in situ observation data from the WGs and buoys with satellite data measured by the sensor with different frequencies and ocean models. Furthermore, we plan to develop models for estimating SST at different depths and predicting SST.
Acknowledgements:
This work was supported by internal funding from the Okinawa Institute of Science and Technology Graduate University, and was partly funded by a Grant-in-Aid for Scientific Research (JP22K03725) from the Japan Society for the Promotion of Science in providing knowledge of typhoons and the Himawari-9 satellite.
References:
[1] N. Kosaka, et al., “Sea surface typhoon observations using autonomous surface vehicles in 2024,” IWTRC-2, 2024.
[2] Peter Minnett and Andrea Kaiser-Weiss, “Near-surface oceanic temperature gradients,” GHRSST, Discussion document, 2012. https://www.ghrsst.org/wp-content/uploads/2021/04/SSTDefinitionsDiscussion.pdf
[3] K. Bessho, et al., “An Introduction to Himawari-8/9 — Japan’s New-Generation Geostationary Meteorological Satellite,” J. Meteor. Soc. Japan, 94, 151-183. doi:10.2151/jmsj.2016-009
In situ observation data are acquired using two wave gliders (WGs) (SV2 and SV3) provided by Liquid Robotics, Inc., which have experienced typhoon observations [1]. A WG is composed of a sea surface float, a submerged glider and a connecting cable and equipped with a suite of customizable sensors for SSTs. A conductivity-temperature-depth sensor (CTD: Sea-Bird Scientific) installed on the glider. The length of the cable varies depending on the type of WG; SV2 at 6.5m and SV3 at 8.5m. An acoustic doppler current profiler (ADCP: Teledyne Marine, Workhorse ADCP) is mainly used to measure currents, but can also measure seawater temperature, and installed on the bottom of the float. As the WG measures SSTs at multiple water depths, we will analyze the diurnal variations caused by solar radiation across these depths (Fig.1). The weather from Aug. 8 to 15 in 2024 was mostly sunny, leading to large daily fluctuations in SSTs. After that, the weather turned to rainy and cloudy conditions, and typhoon ‘JONGDARI’ developed near the observation point on Aug. 19. SSTs had dropped by approximately 1°C. In addition to using the WG, we conducted SST observations with two drifting buoys (Buoy1 and Buoy2) at a water depth of nearly 0 m. SSTs measurements from the ADCP and drifting buoys represent SST_subskin, while the CTD data from the WGs represent SST_depth: SST_6.5m for SV2 and SST_8.5m for SV3, which classifies several types of SSTs at different seawater depths [2]. The SST measurable by satellite remote sensing varies depending on the wavelength and frequency of the electromagnetic waves [2]. SST_skin is primarily measured using infrared satellite sensors, which capture data at a depth of approximately 10-20 μm. On the other hand, SST_subskin is measured using microwave radiometers operating in the 6-11 GHz frequency range, at depths less than 1 m. SST_depth refers to the temperature at a specific water depth that cannot be measured using satellite-based remote sensing due to the absorption and emission characteristics of radiation within the ocean's surface layer. Fig.2 shows comparison of SSTs measured by buoys with satellite named Himawari-9 [3] using infrared sensor. While the satellite measures and retrieves SSTs at shallower depths compared to buoys, the daily patterns of seawater temperature fluctuations caused by solar radiation show good agreement between the two.
In this experiment, we observed variations in SST values among sensors installed at different depths. Since the sensor types and their performance differ, we plan to conduct comparative evaluations at multiple depths using identical sensors in future. Additionally, a comparison of SSTs measured by the buoys and satellite demonstrated that SSTs are warmed by solar radiation, with daily fluctuation patterns showing strong similarity. We aim to compare in situ observation data from the WGs and buoys with satellite data measured by the sensor with different frequencies and ocean models. Furthermore, we plan to develop models for estimating SST at different depths and predicting SST.
Acknowledgements:
This work was supported by internal funding from the Okinawa Institute of Science and Technology Graduate University, and was partly funded by a Grant-in-Aid for Scientific Research (JP22K03725) from the Japan Society for the Promotion of Science in providing knowledge of typhoons and the Himawari-9 satellite.
References:
[1] N. Kosaka, et al., “Sea surface typhoon observations using autonomous surface vehicles in 2024,” IWTRC-2, 2024.
[2] Peter Minnett and Andrea Kaiser-Weiss, “Near-surface oceanic temperature gradients,” GHRSST, Discussion document, 2012. https://www.ghrsst.org/wp-content/uploads/2021/04/SSTDefinitionsDiscussion.pdf
[3] K. Bessho, et al., “An Introduction to Himawari-8/9 — Japan’s New-Generation Geostationary Meteorological Satellite,” J. Meteor. Soc. Japan, 94, 151-183. doi:10.2151/jmsj.2016-009