A TECHNIQUE FOR REMOVING PLATFORM VIBRATION NOISE FROM A PULSED LADARVIBRATION SENSOR

A technique has been developed for removing platform-induced vibration noise from a pulsed ladar vibration sensor. Deriving the vibrational characteristics of the platform is accomplished by simulating ambient atmospheric aerosols as a stationary reference target. Using a pulsed coherent detection ladar, the instantaneous Doppler frequency shifts f rom both aerosols and a distant hard target are measured and recorded, while the data acquisition is range gated so that both Doppler measur ements are made from a single pulse. Periodic measurements are then ma de to develop a time history of the fluctuations in the Doppler signal s, after which two vibration spectra are derived by Fourier transformi ng the time histories of the instantaneous Doppler shifts. The first s pectrum contains information regarding the relative motion between the target and platform, while the second spectrum contains information r egarding the relative motion between the platform and the stationary a erosols. When the second spectrum is subtracted from the first, the re sulting spectrum is the true vibrational signature of the target, The advantages of this new technique over conventional continuous wave lad ar vibration sensors are: target range information is obtainable; the average power required from the laser is significantly reduced; and ad ditional sensing equipment is not needed to derive the platform-induce d noise spectrum. The principles of this technique are experimentally verified using a 2 mu m pulsed ladar.