NASA pioneered Navigation Doppler LiDAR (NDL) for precision navigation and executing well-controlled landings on surfaces like the Moon. The LiDAR sensor utilizes Frequency Modulated Continuous Wave (FMCW) technique to determine the distance to the target and the velocity between the sensor and target.
Specifically, homodone sensors obtain the changes in signal frequency between the received and reference frequencies for calculating both speed and distance. However, homodyne detection cannot provide any phase information. This is a problem because the current sensor cannot determine the sign (+/-) of the signal frequencies, resulting in false measurements of range and velocity.
NASA has developed an operational prototype (TRL 6) of the method and algorithm that works with the receiver to correct the problem. Using a three-section waveform and an algorithm to resolve ambiguities in sign when the signal is compromised, the algorithm analyzes historical phase information to interpret the sign of the remaining frequencies and recover the phase information that contains valuable measurement information.
The system has several applications in self-driving cars where it can provide both 3D range and Doppler images of surroundings, aircraft navigation in which it can allow navigation in GPS-denied environments, general automated rendezvous and docking where it can provide relative position, approach velocity, and attitude of the docking port, as well as space where NDL can enable precision navigation to the desired landing location for future large robotic and crewed landing missions.