ance travelled
igational com-
gyros and to
| which is re-
ined by means
RATORS
ME
m is stable in
1e start of the
Ys polar axis;
m a horizontal
axes in such a
'ast-west.
platform will
per hour with
p the accelero-
itinuously with
horizontal, no
jy acceleration,
f the starting
tion “latitude”
SURVEY NAVIGATION, CORTEN 83
and “longitude” will not change as long as there is no other movement than the earth’s
rotation and its exact compensation at the horizontal platform.
After the vehicle started moving, say, in north-south direction, accelerations will be
supplied to the accelerometers, the resulting electrical signal (ay) supplied to the in-
tegrators; a first integration will transform the acceleration (ay) into the north-south
^f 2
speed V, | ay .dt and a second integration will transform this speed (Vy) into the
0 2
^
north-south distance travelled sy = | Vy.dt; the final output of the integrators is
0
proportional to the distance travelled s, — | [ay .dt2. The navigational computer adds
HORIZONTAL PLATFORM
WITH NS ACCELEROMETER - | EQUATOR
GYROSCOPES ———— ,. CLOCK
STABLE PLATFORM —
Fig. 23.
this distance, expressed in latitude coordinate distance, to the latitude of the starting
point which was introduced into the system before the start. The final indication will
continuously show the latitude (q) of position. The horizontal platform, however, needs
a continuous correction about the E-axis in order to keep its horizontal attitude (figure
23).
This compensation for the vehicle’s north-south displacement is applied by the same
latitude displacement information: the distance travelled is not only fed into the navi-
gational computer but also into the correction computer which rotates the E-axis over
angle y in order to keep the accelerometer platform horizontal. If the movement takes
place in an arbitrary direction, the acceleration ap caused by the east-west movement
vector is measured and integrated in the same way as ay. In addition, however, the dis-
placement must be multiplied by ms in order to compensate for the varying lengths of
the parallels. The information about the longitude of position is used by the navigational
computer to add À to the original longitude of the starting point, and by the correcting
computer to rotate the accelerometer platform about the polar axis in order to keep the
platform horizontal during the east-west displacement 2. Corrections for a-sphereicity of
the earth and for coriolis accelerations must also be applied.
Performance of inertial systems.
There are two main causes of errors in inertial navigation systems:
