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###  Magnetic Data Processing on R/V Melville  ###
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Description by S.M.Smith, SIO/GDC, January 1995

DATA LOGGING:
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Earth total field magnetic data are collected from a Geometrics Mod.
801 Marine Proton magnetometer and logged by program 'mag-log' on the
realtime computer (mlvl61).  An analogue paper record is also recorded
with two pens, one at 100 nT full scale and a second at 1000 nT full
scale.

Time and magnetic total field value in nanoTesslas from each
magnetometer 5.5 second cycle  are logged to realtime log file 'MAGinpf'.
Once each day the file is timestamped with the date and this
MAGinpf.[date] file is transferred to the offline machine for
postprocessing.  See 'MAGinpf.file.description'.

NEAR REALTIME DISPLAY (on mlvl61):
---------------------------------
Magnetic total field is displayed in the "Lab-Display' window on the
u/w watch terminal and is updated at approximately 1 minute intervals.

Profiles of magnetic total field vs time going back for about the last
12 hours can be displayed in a window of the u/w watch terminal by
executing program 'profile'(??change name). (program DOget.MAGinpf
must be running to make data available to the 'profile??' program.)

A profile of the magnetic anomaly (IGRF removed) residuals can also
be displayed along track on the Realtime navigation plot.

DATA PROCESSING:
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The MAGinpf file is input to program 'MAGconvert' which averages
the data for 1 minute intervals and writes a file,
'mag_uwts.[date]'. (See mag_uwts.file.description). This file is passed
through program 'uwchek' which checks the file for time gaps and flags
consecutive values whose difference exceeds the range specified.  The
mag_uwts.[date] file is then concatenated with the previous mag_uwts
files into a cumulative file, mag_uwts.[CRUISE], which is merged by
program 'uwmerg' with navigation, depth and gravity into a binary 
file, 'uwmrg.[CRUISE]' (see 'uw_merge.description').

The magnetic anomaly is calculated during merging by subtracting
the International Geomagnetic Reference Field (IGRF) from the total
field value. (The IGRF is calculated by determining the IGRF values
at the corners of a one degree square centered on the first point
and then interpolating the IGRF on this plane as long as the location
of subsequent values stay within the one degree square.)

#end