Validating Pressure Gauges for Seafloor Seismology and Geodesy

海底压力计长期以来一直是海洋观测的重要工具，现在是海底地震仪系统的关键传感器。三种不同的传感器，水听器，差压传感器（DPG）和高分辨率绝对压力计（APG），都被使用，因为没有一个传感器覆盖记录所有地震或海洋相关压力信号所需的所有频率。 一个长期存在的问题是，一直没有办法在与地震学相关的频率和适当的温度和压力下准确地校准这些传感器。将在高压设施内建立和安装一个传感器相互校准系统，以校准不同的传感器。新的校准方法可适用于科学界以前存档的许多数据集，也可适用于今后的海底数据，以提高数据的有用性。 研究的第二个组成部分将是分析最近在海底部署的新系统的数据，该系统用于重新校准海底压力计，以消除校准中的长期变化（漂移）。无漂移或几乎无漂移的海底压力测量方法的发展，将开启迄今为止不可能观测到的与地震灾害有关的断层过程和有助于验证海洋学长期变化的洋流。作为一名早期职业生涯的博士后科学家，他将领导大部分研究工作。将在实验室高压设施中建造并安装一个用于校准海底地震学相关频率（0.001至50 Hz）的海洋压力计的系统，以实现DPG、APG和水听器响应的准确相互比较。 APG的校准目前在低频下是众所周知的，但在短周期下是未知的。水听器校准仅在高频时准确。由于传感器响应的温度和压力依赖性以及与机械顺应性相关的可能变化，DPG校准在所有频率下都是不确定的。 该研究旨在通过首次在所有相关频率上完全校准传感器并寻找传感器功能中可能存在的问题，来消除我们对这些仪表响应的理解中存在的任何不确定性。 对最近在新西兰和阿拉斯加部署的地震和压力传感器记录的大地震信号进行分析，将用于确认传感器校准。将压力测量应用于洋流研究和海底大地测量受到漂移的限制，漂移是指压力计校准随时间缓慢变化。在阿拉斯加和新西兰近海部署了一年之久，最近回收了5台仪器，在其上安装了一个用于校准海底绝对压力计的“A-0-A”系统。双压力表的输入定期切换，以测量仪表外壳内的压力，并使用气压计的数据进行验证。在高压（海底）下的漂移预计会跟随在低压下测量的漂移，因此可以从高压数据中减去漂移。来自双压力计的数据（以不同的速率漂移）将被比较，以评估这种消除漂移的新方法的准确性。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Seafloor pressure gauges have long been an essential tool for oceanographic observations and are now a critical sensor deployed with seafloor seismometer systems. Three different sensors, the hydrophone, differential pressure sensor (DPG) and the high-resolution absolute pressure gauges (APG), are all used because no one sensor covers all frequencies necessary to record all seismically or oceanographically relevant pressure signals. A long-standing problem has been that there has been no means to accurately calibrate these sensors at frequencies relevant to seismology and at appropriate temperatures and pressures. A system for inter-calibration of the sensors will be built and installed within a high-pressure facility to make calibrations of the different sensors. The new calibrations can be applied to many previous data sets archived by the scientific community and to future seafloor data enhancing the usefulness of the data. A second component of the research will be to analyze data from recent seafloor deployments of a new system for recalibrating pressure gauges at the seafloor to remove long term variations in the calibration (drift). The development of drift free or nearly drift free methods for measuring seafloor pressure will open heretofore impossible observations of faulting processes relevant to seismic hazard and of oceanographic currents helping to validate long term changes in oceanography. An early career, postdoctoral scientist will lead much of the research.A system for calibrating marine pressure gauges at frequencies relevant to seafloor seismology (0.001 to 50 Hz) will be constructed and installed in a laboratory high pressure facility to enable accurate inter-comparison of the responses of DPGs, APGs and hydrophones. The calibration of APGs is currently well known at low frequency but unknown at short period. Hydrophone calibrations are only accurate at high frequency. DPG calibrations are uncertain at all frequencies due to temperature and pressure dependencies of the sensor response and possible variations related to mechanical compliance. The research seeks to eliminate any remaining uncertainties in our understanding of the response of these gauges by calibrating the sensors completely over all relevant frequencies for the first time and searching for possible problems in sensor function. An analysis of signals from large earthquakes on seismic and pressure sensors recorded during recent deployments in New Zealand and Alaska will be used to confirm sensor calibrations. Application of pressure measurements to the study of oceanographic currents and to seafloor geodesy is limited by drift - the slow variation in calibration of the pressure gauges with time. A system “A-0-A” for calibrating absolute pressure gauges at the seafloor was installed on 5 instruments recently recovered from year-long deployments offshore of Alaska and New Zealand. The inputs to dual pressure gauges are periodically switched to measure the pressure within the instrument housing which is verified using data from a barometer. The drift at high (seafloor) pressure is expected to follow the drift measured at low pressure and thus the drift can be subtracted from the high-pressure data. The data from the dual pressure gauges (which drift at different rates) will be compared to assess the accuracy of this new method for the removal of drift.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.