  Scanning Laser Doppler Vibrometer (SLDV) measurements are affected by sensor
head vibrations as if they are vibrations of the target surface itself. This
paper presents practical correction schemes to solve this important problem.
The study begins with a theoretical analysis, for arbitrary vibration and any
scanning configuration, which shows that the only measurement required is of
the vibration velocity at the incident point on the final steering mirror in
the direction of the outgoing laser beam and this underpins the two correction
options investigated. Correction sensor location is critical; the first scheme
uses an accelerometer pair located on the SLDV front panel, either side of the
emitted laser beam, while the second uses a single accelerometer located along
the optical axis behind the final steering mirror. Initial experiments with a
vibrating sensor head and stationary target confirmed the sensitivity to sensor
head vibration together with the effectiveness of the correction schemes which
reduced overall error by 17 dB (accelerometer pair) and 27 dB (single
accelerometer). In extensive further tests with both sensor head and target
vibration, conducted across a range of scan angles, the correction schemes
reduced error by typically 14 dB (accelerometer pair) and 20 dB (single
accelerometer). RMS phase error was also up to 30% lower for the single
accelerometer option, confirming it as the preferred option. The theory
suggests a geometrical weighting of the correction measurements and this
provides a small additional improvement. Since the direction of the outgoing
laser beam and its incident point on the final steering mirror both change as
the mirrors scan the laser beam, the use of fixed axis correction transducers
mounted in fixed locations makes the correction imperfect. The associated
errors are estimated and expected to be generally small, and the theoretical
basis...
