Development of an in situ self calibrating ocean bottom pressure meter (OBP)

海底静水压力监测在海洋大地测量学、海洋油气储层监测、海洋学和卫星重力产品验证等多个海洋学科中发挥着关键作用。但是，从40多年前的最初日子到今天，高分辨率传感器始终受到传感器校准缺乏长期稳定性的影响，从而阻止了对所有这些学科的长期趋势的明确检测。我们的目标是开发、测试,并构建一个原位self-calibrating海底压力计,这是能够监视和明确认识到长期压力变化在海底由于其内置drift-quantification精度优于10 Pa即1毫米水柱相当于通过调查(一个或多个年)的长度,因此解决预期的趋势——一个任务,没有仪器能够应付目前。我们的方法是测量环境压力和冻结参考压力之间的差值。仪器在海底部署后，通过关闭阀门，在一个腔室中捕获参考压力。这种长期监测概念的创新之处在于将差压传感器与温度补偿参考压力室结合使用，这种策略结合了显著减少漂移和简单的原位校准的优点。由于相对压力的动态范围比海底绝对压力（潮汐高度而不是整个海洋深度）小三个数量级，因此可以实现较小的仪器漂移（漂移幅度随传感器的满量程变化）。在测量开始和结束时，由于物理压差为零，因此将缩短差压传感器的两个端口，从而获得漂移的量化。挑战是通过智能选择材料、几何形状和温度监测来减少参考压力中温度引起的噪声，并严格避免参考系统中甚至最小的潜在泄漏。与唯一已知的竞争方法（通过自重测试仪对绝对压力传感器进行原位校准）相比，我们的策略具有四个关键优势：传感器漂移更少，鲁棒性更强，成本更低，因此可以选择将仪器安装在地理传感器网络中。我们计划设计，测试和调查一个非常基本的系统，以评估优点和缺点以及改进的选择（概念证明）。在第二步中，我们希望从这个原型中获得新的见解和经验，以建立一个有可能成为深海长期原位压力观测新标准的仪器。

Monitoring hydrostatic pressure at the seafloor plays a key role in several marine disciplines like marine geodesy, marine hydrocarbon reservoir monitoring, oceanography and the validation of satellite gravity products. But since its initial days more than 40 years ago down until today the high resolution sensors unchangedly suffer from a lack of long-term stability of the sensor calibration, preventing the unequivocal detection of long-term trends in all these disciplines.Our goal is to develop, test and build an in situ self-calibrating ocean bottom pressure meter, which is able to monitor and unequivocally recognize long-term pressure variations at the seafloor due to its built-in drift-quantification with a precision of better than 10 Pa i.e. 1 mm water column equivalent through the length of survey (one or multiple years) and therefore to resolve the expected trends - a task, which no instrument is able to cope with presently. Our method is to measure the difference between the environmental pressure and a frozen-in reference pressure. The reference pressure is captured in a chamber by closing the valve to the environment after the instrument was deployed at the seafloor. The innovative aspect of this concept for long-term monitoring is the combined usage of a differential pressure sensor with a temperature compensated reference pressure chamber, a strategy combining the advantages of significantly less drift and simple in situ calibration.Three orders less instrumental drift will be achieved, as the dynamic range of relative pressures is three orders less compared to absolute seafloor pressures (tidal height instead of full ocean depth) thus allowing smaller full scale of the sensor (drift amplitude scales with the full scale of the sensor). Quantification of the drift will be gained shorting both ports of the differential pressure sensor at the beginning and at the end of the survey, as the physical pressure difference then is zero. The challenge is to reduce temperature-caused noise in the reference pressure by intelligent choice of materials, geometry and temperature monitoring and to avoid rigorously even minimal potential leaks in the reference system.Our strategy has four crucial advantages over the only known competing approach, the in situ calibration of an absolute pressure sensor by means of a deadweight tester: Less sensor drift, more robustness and minor cost with the resulting option to install the instruments in geo-sensor networks.We plan to design, test and investigate a very basic system, to evaluate strengths and weaknesses as well as the options for an improvement (proof of concept). In a second step with a second proposal we want to implement the new insights and experiences from this prototype to build an instrument which has the potential to become the new standard for long-term in situ pressure observations in the deep sea.