Acquisition, Deployment, and Testing of an Absolute Quantum Gravity Meter
Abstract
We propose to acquire and deploy a new type of absolute gravity meter: the lasercooled atom interferometer type, which is now commercially available. We have three objectives: 1) test the accuracy, repeatability, robustness, and response to environmental conditions; 2) resurvey a number of locations in California previously surveyed with an absolute gravity meter to determine water table changes over the past three decades; 3) begin the process of adapting the quantum gravity meter to seafloor applications. This research will address three items enumerated in the BAA: I.9.2.9, Underwater Sensors; I.9.2.11, Corrections of Signals in Next Generation sub-micro-Gal Absolute Gravimeter Measurements; and I.9.2.21, Understanding Water budgets. The primary research goal is to gain experience with the new cold atom interferometric technology for gravity measurement. Compared to the existing free-fall methods, the quantum gravity meter promises higher accuracy, better robustness for continuous operation, and recoilless measurements (ground recoil is an effect that has prevented successful free-fall measurements on the seafloor). In our technical approach we plan a series of accuracy tests on our laboratory shake-table and in our cold vault, the collection of a long time-series at our geophysical observatory to search for correlations with other environmental factors, a re-survey of absolute sites in California established in the 1980s to gain ground water information, and an assessment of the steps needed to adapt the system to seafloor use. If the technology stands up to our series of experiments and deployments we anticipate an outcome that includes expanded use of absolute gravity to study water table changes and a roadmap to the establishment of absolute gravity sites on the seafloor. The utility of extending repeated absolute gravity measurements to the seafloor has been recognized for some time. The rate of uplift or subsidence near mid-ocean ridges or subduction zones could be determined, magma motions could be detected, the details of ocean-crust deformation could be established, and even sea level variations in the middle of the ocean, far from land based tide gauges, could be tracked. Few viable methods exist to detect long term vertical motions of the seafloor. The capability to measure gravity with 1 part in 109 accuracy (corresponding to a height sensitivity of 3 to 5 mm) on the bottom of the ocean would truly be transformative to marine geodesy and geodynamics.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 06, 2020
- Source ID
- HM04761912008
Entities
People
- Mark A. Zumberge
Organizations
- National Geospatial-Intelligence Agency
- University of California, San Diego