9.8 External velocity
If the ADMA is supplied with an external velocity signal, the orientation angles for roll and pitch do
not drift, thus permitting measurements over longer periods.
Supply of an external velocity signal allows the ADMA to calculate a relative position using the method
of dead reckoning. In this case, the position error no longer increases quadratically with time, but
instead exhibits a linear behaviour. The position is relative to the measurement's starting point and
depends on the course as well as the external velocity.
ADMA with external velocity measurement and DGNSS
As with pure (D)GNSS augmentation, this operating configuration constitutes the most advanced
system stage providing the best possible performance. A determination of absolute positions with
(D)GNSS allows the most accurate inertial measurements.
Should the reception of the (D)GNSS data be interrupted, position measurement is performed by the
ADMA. But with augmentation available (external velocity measurement) a dead reckoning position
can be calculated. Thus, the position accuracy degrades only linearly during GNSS outages. On re-
entry of valid (D)GNSS data the ADMA takes up GNSS/INS operation again.
Optionally, a dual-antenna DGNSS capable of calculating course and yaw angle can be used. The
starting alignment is automatically detected at the beginning of a measurement as well.
The ADMA has implemented an “Extended Kalman filter”, which during the ADMA GNSS/INS-mode
determines and compensates possible errors of the external velocity signal, like bias and scale factor.
Consequently, there is a calibrated speed signal even with a GNSS outage occurring.
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