Temperature correction and usefulness of ocean bottom pressure data from cabled seafloor observatories around Japan for analyses of tsunamis, ocean tides, and low-frequency geophysical phenomena

Daisuke Inazu,Ryota Hino

doi:10.5047/eps.2011.07.014

Abstract

Ocean bottom pressure (OBP) data obtained by cabled seafloor observatories deployed around Japan, are known to be significantly affected by temperature changes. This paper examines the relationship between the OBP and temperature records of six OBP gauges in terms of a regression coefficient and lag at a wide range of frequencies. No significant temperature dependency is recognized in secular variations, while substantial increases, at rates of the order of 1 hPa/year, are commonly evident in the OBP records. Strong temperature dependencies are apparent for periods of hours to days, and we correct the OBP data based on the estimated OBP-temperature relationship. At periods longer than days, the temperature corrections work well for extracting geophysical signals for OBP data at a station off Hokkaido (KPG2), while other corrected data show insufficient signal-to-noise ratios. At a tsunami frequency, the correction can reduce OBP fluctuations, due to rapid temperature changes, by as much as millimeters, and is especially effective for data at a station off Shikoku (MPG2) at which rapid temperature changes most frequently occur. A tidal analysis shows that OBP data at a station off Honshu (TM1), and at KPG2, are useful for studies on the long-term variations of tidal constituents.

Highlights

Pressure sensor units for oceanographic applications have been employed since the late 1960’s (e.g., Munk and Zetler, 1967)
Data We examine Ocean bottom pressure (OBP) data obtained at six ocean bottom tsunami meters (OBTMs) deployed on three cabled observatories (Fig. 1)
We examine the relationship between the OBP and temperature records obtained by the OBTMs

Summary

Introduction

Pressure sensor units for oceanographic applications have been employed since the late 1960’s (e.g., Munk and Zetler, 1967). Seven cabled observatories utilizing HP pressure gauges around Japan are operated by JMA, the National Research Institute for Earth Science and Disaster Prevention (NIED), the Earthquake Research Institute of the University of Tokyo (ERI), and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) (Hirata et al, 2009) These HP pressure gauges show a fairly good ability to observe tsunamis of the order of millimeters (Hino et al, 2001; Hirata et al, 2003; Baba et al, 2004; Tanioka et al, 2004; Satake et al, 2005; Saito et al, 2010), there have been no reports of successful observations of low-frequency (

OBP Records and Remaining Temperature Dependency

Lagged Correlation Analysis of the OBTM Data

Usefulness of the OBTM Data after Temperature Corrections

Tidal Frequency Bands—Evaluating Seasonal Variations of Tidal Constituents