Autonomous navigation systems tend to drift over time as errors accumulate. Position fixing uses GPS, or similar technologies, to reference location and correct for this effect. However, GPS is sensitive to jamming and external interference, so it is important to develop navigation systems that do not depend on it. Other position fixing alternatives, such as terrain referencing and scene matching, are limited in their operation over water.

To address this need, Phillips et al. simulated the motion of a vehicle while it used a position fixing method based on gravity measurements.

“If you block GPS, then the inertial system will start to drift again, so what people want is the ability to provide this position fixing independent of GPS,” said author Jason Ralph. “The advantage of using gravity is that gravity is impossible to block.”

The technique obtains partial gravity gradient solutions from cold atom interferometers, then references existing gravity databases to determine location.

Cold atom interferometers measure the local gravity gradient by dropping cold atoms and use a series of light pulses to split and recombine the matter waves. The output of these interferometers is sensitive to the acceleration of gravity with almost no drift. Classical systems can accomplish the same task, but they require constant recalibration. The quantum version avoids this necessity and has the potential for absolute and ultra-precise measurements.

The team modeled a trajectory of over 1000 kilometers that crossed land and water, as well as regions of lower and higher resolution gravity data. The sensor parameters used in the model are reasonable compared to the current generation of cold atom interferometers. Because of this, they hope to collect data with existing sensors to compare to the models.

Source: “Position fixing with cold atom gravity gradiometers,” by Alexander M. Phillips, Michael J. Wright, Isabelle Riou, Stephen Maddox, Simon Maskell, and Jason F. Ralph, AVS Quantum Science (2022). The article can be accessed at