2:00 PM - 2:15 PM
[SCG45-14] Characteristic of depth dependence and annual variation of OBP time series in DONET
Keywords:Marine geodesy, Ocean Bottom Pressure gauge, DONET
Ocean Bottom Pressure-gauge (OBP) is extremely important sensor to observe the continuous seafloor vertical deformation. The observed OBP data, however, contain not only the signal of crustal deformation but also the other components such as tidal-component, non-tidal oceanographic fluctuation, and sensor specific drift. Therefore, appropriate assessment of these contributions are essentially important to extract the signal of crustal deformation. Especially, the non-tidal oceanographic fluctuation is the largest noise because of its similarity in time constant to the crustal deformation. The non-tidal oceanographic model (e.g., Inazu et al., 2012) is one of the candidate to estimate its contribution. Dobashi and Inazu (2021) compared the time series of observed data with non-tidal oceanographic models in short-term time series (3-90 days) to evaluate the contribution of the non-tidal fluctuation on OBP data. In contrast, almost all previous studies did not assess the characteristics of non-tidal oceanographic component in long-term data more than several years. In this study, we investigate the long-term spatio-temporal characteristic of non-tidal oceanographic fluctuation based on the data of DONET OBP time series.
In this study, we used the 8-year continuous data between 2012 to 2019 for analyses. DONET observation network extends 200km east-west, 100km north-south, and 1-4km sea depth. Ocean tide components were removed by tide-killer filter (Hanawa and Mitsudera, 1985), and instrumental drift were approximated and removed by linear and exponential functions.
Firstly, the similarity of OBP time series of each stations was evaluated using distance and difference of sea depth between stations as indicators. We assumed a reference site, which locates in the most north-eastern part of the network, and the sea depth of the site is 2039m. We subtracted the time series of the reference site from all of the DONET sites. The standard deviation of the relative pressure time series was calculated and their dependence on station distance and sea depth difference was evaluated. The correlation coefficient with the station distance was quite small (0.15). In contrast, the correlation coefficient with the sea depth difference was 0.69. It may indicate that effective removal of the non-tidal oceanographic fluctuation is possible by selecting the reference site considering the sea depth difference rather than the distance. Secondly, we estimated the amplitude and phase of the annual component of OBP time series to evaluate the annual fluctuation based on 8-year data. Estimated amplitude and phase of the annual component also clearly show the dependency with difference of sea depth. These results suggest that the annual component is a main factor in the sea depth dependence of the non-tidal component. In the presentation, we also evaluate the temporal variation of the characteristic of the annual component.
In this study, we used the 8-year continuous data between 2012 to 2019 for analyses. DONET observation network extends 200km east-west, 100km north-south, and 1-4km sea depth. Ocean tide components were removed by tide-killer filter (Hanawa and Mitsudera, 1985), and instrumental drift were approximated and removed by linear and exponential functions.
Firstly, the similarity of OBP time series of each stations was evaluated using distance and difference of sea depth between stations as indicators. We assumed a reference site, which locates in the most north-eastern part of the network, and the sea depth of the site is 2039m. We subtracted the time series of the reference site from all of the DONET sites. The standard deviation of the relative pressure time series was calculated and their dependence on station distance and sea depth difference was evaluated. The correlation coefficient with the station distance was quite small (0.15). In contrast, the correlation coefficient with the sea depth difference was 0.69. It may indicate that effective removal of the non-tidal oceanographic fluctuation is possible by selecting the reference site considering the sea depth difference rather than the distance. Secondly, we estimated the amplitude and phase of the annual component of OBP time series to evaluate the annual fluctuation based on 8-year data. Estimated amplitude and phase of the annual component also clearly show the dependency with difference of sea depth. These results suggest that the annual component is a main factor in the sea depth dependence of the non-tidal component. In the presentation, we also evaluate the temporal variation of the characteristic of the annual component.