The delta Doppler technique for LDV measurements at long distances
Abstract
A technique for measuring velocity, referred to as a Delta Doppler technique, was presented. This technique determines scattering source velocities by measuring the difference in Doppler shifts of two different frequencies. By transmitting the two frequencies along the same path, a moving fringe pattern is established such that a nonmoving scatterer at the sensing volume would see an intensity variation exactly equal to the difference in the transmitted frequencies. If the particle has a velocity component along an axis which bisects the angle formed by the transmitter and receiver axes, a Doppler shift in the difference frequency can be measured and the velocity component computed. The frequency measured would correspond to the difference in Doppler frequencies that two laser Doppler velocimeters using separate frequencies (the same frequencies as used previously) would have measured, thus the term Delta Doppler.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 February 1976
 Bibcode:
 1976STIN...7620464C
 Keywords:

 Doppler Effect;
 Frequency Shift;
 Velocity Measurement;
 Diffraction Patterns;
 Electromagnetic Scattering;
 Laser Doppler Velocimeters;
 Low Frequencies;
 Paths;
 Velocity;
 Lasers and Masers