  The demand from industry to produce accurate acceleration measurements down
to ever lower frequencies and with ever lower noise is increasing. Different
vibration transducers are used today for many different purposes within this
area, like detection and warning for earthquakes, detection of nuclear testing,
and monitoring of the environment. Accelerometers for such purposes must be
calibrated in order to yield trustworthy results and provide traceability to
the SI-system accordingly. For these calibrations to be feasible, suitable
ultra low-noise accelerometers and/or signal processing functions are needed.
Here we present two digital signal processing (DSP) functions designed to
measure ultra low-noise acceleration in calibration systems. The DSP functions
use dual channel signal analysis on signals from two accelerometers measuring
the same signal and use the coherence between the two signals to reduce noise.
Simulations show that the two DSP functions are estimating calibration signals
better than the standard analysis. The results presented here are intended to
be used in key comparison studies of accelerometer calibration systems, and may
help extend frequency range down to ultra-low frequencies of around 10mHz.
