Applanix POS MV 320 - Heave Filter

POS MV V4 User Guide
Theory of Operation
Copyright © Applanix Corporation, 2009
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Generally, the housing of the INS (the IMU in POS MV) is assumed to be
aligned with the inertial sensor frame. With the inertial sensor installed so that
its x, y and z axis coincide with the forward, starboard and down directions of
the vessel hull respectively, the INS will measure the vessel roll, pitch and
heading directly. Otherwise, the INS must apply a constant installation offset
transformation to the computed roll, pitch and heading to transform the inertial
sensor assembly attitude to the hull attitude.
POS MV includes a user orientation input capability. This makes it possible to
correct the orientation of the IMU so that it delivers measurements valid for an
alternative reference frame, such as that of a multi-beam transducer or of the
vessel.
The small size and lightweight of the IMU allow it to be mounted directly on
the multi-beam transducer. From here, it can measure the transducer position
and orientation directly.
Heave Filter
POS MV measures heave by performing a double integration on the
measurements of vertical acceleration computed by the strap-down navigator,
see
Figure 68.
The high pass filter limits the appearance of noise in the vertical
measurement channel caused by the strap-down navigator. Sources of such
noise could include Schuler oscillations, GNSS noise, etc.
The performance characteristics of the heave filter are:
• Filter settling time
• Steady state heave error