User manual

IMPORTANT
Non-standard ACM settings will affect system operation during a deployment and are not
recommended.
Spin Test
A spin test is conducted to generate compass calibration corrections for post-processing
use. The spin test data is collected by rotating the profiler on its base and aligning the sting to the
eight cardinal points of the compass in sequence.
Corrected
Corrected
H
CorrectedH
CorrectedH
HY
HX
HY
HX
=
=
=
θ
θ
θ
tan
cos
sin
This compass calibration procedure is described Chapter 8 “Data Offload, Processing,
and Interpretation”. The heading calculations described above could then be applied to the
corrected data without the need for horizontal normalization, which is included in the calibration.
The final four numbers in each ACM scan are the velocities along the acoustic axes of the
sting. The units are cm/s. The fingers of the sting are labeled +X, +Y, -X, and -Y. The first
velocity in a scan is from the +X path, the second is from +Y, the third is from -X, and the fourth
velocity is from the -Y path. By convention, the sting is mounted on the MMP with the -Y finger
up. This places the +Y finger down, the +X finger facing left, and the -X finger facing right.
For the X fingers, velocity is defined to be positive for flow along the acoustic path from
the central post of the sting towards the finger. For the Y fingers, velocity is defined to be
positive for flow along the acoustic path from the finger towards the central post. With the sting
pointed into the flow, the raw X-path velocities will be positive and the raw Y-path velocities will
be negative. The angle between the acoustic paths and the central post is 45°.
These definitions and relationships are summarized in Figure G-28. The arrows indicate
the direction of positive flow along each acoustic path. The parenthetical values indicate the
G-22