User manual

Table Of Contents
4. Offset and scale factors will be displayed in the ‘Offset’ and ‘Scale’ text boxes. The
plot window will display the corrected and uncorrected data. If the data were in an
eight element file named spintest, the eight angular biases and the average angular
bias will also be displayed.
5. Repeat steps 3 to 5 to process additional data files. Click ‘Quit’ to exit the program.
6. The plots can be printed or saved to a file using the icons in the tool bar at the top of
the plot window and the options in the ‘File’ menu of the plot window.
Applying the Compass Correction Parameters
The compass correction parameters are applied to the raw data in two stages First, the
offsets are subtracted from the raw measurements and the results are divided by the scale factors
to produce MX and MY.
S
O
CORRECTED
S
O
CORRECTED
Y
YHY
HYMY
X
XHX
HXMX
==
==
DEVTH
MB
MY
MX
++
=
1
tan
θ
True heading is then calculated from the corrected compass components as:
M
DEV
, the magnetic deviation, is available from independent sources. B
T
is calculated at
eight points by the acm_corr programs. The operator may use the average value of the bias angle
or may perform an interpolation across each octant.
Sensor Calibration
The Cartesian co-ordinate frame of the MMP is defined to have the +x-axis pointing
forward, the direction in which the sting of the ACM points. The +y-axis points to port, the left
side of the profiler. The +z-axis points up, completing a right-handed Cartesian system. The first
two numbers in each ACM scan are TX and TY, the tilt angles of the x- and y-axes about the y-
and x-axes. When the ACM pressure housing, which contains the tilt and compass modules, is
properly oriented in the profiler, TX is the pitch angle and TY is the roll angle. TX measures
rotation about the y-axis and is positive when the ACM sting tips up, that is when the profiler tips
backwards. (Note that this is backwards with respect to the usual "right-hand rule" for rotations -
thumb of right hand points in the positive direction along the axis of rotation, fingers of right
Appendix D-4