
MAG/SSMAGinpf.yyyymondd:
        - "SSMAGinpf" file is ASCII format
        - Contains all data and control messages sent to and from the
          towfish, so you will need to parse out the control messages
          to post-process the data.
        - Data structure defined below

The raw data file MAG886inpf.yyyymondd:

Magnetometer (Single Bottle) Format:
*YY.JJJ/HH:MM:SS.S F:FFFFFF.FFF S:SSS D:+DDD.Dm  LL TTTTms_Q:QQ !!!! CR LF
example:
*05.048/23:55:11.0 F:053221.044 S:197 D:+007.4m  L0 0965ms Q:99     

Gradiometer (Dual Bottle) Format:
*YY.JJJ/HH:MM:SS.S F[FFFFFF.FFF SSS TTTT DDDD.D !!!] R[FFFFFF.FFF SSS TTTT DDDD.D !!!] -GRADIENT
example:
*02.233/09:33:45.0 F[056397.170 244 0197 0316.6 ___] R[056397.224 129 0197 0316.8 ___] -000000.054

Number  Description
------  -----------------------------------------------------
Y       Year (time of reading).
J       Julian day (time of reading).
H       Hour (time of reading).
M       Minute (time of reading).
S       Second (time of reading).
F       Magnetic field (nT).
S       Signal Strenght of reading. This is a raw number generated by
        the magnetometer that gives (in part) a good indication of the 
        quality of the final total field measurement. Anything over
        80 is considered an acceptable signal, and anything over 130 is
        considered excellent.
D       Towfish Depth. The value shown is in eteres. The depth sensor is
        generally calibrated prior to deployment by the tech.
L       Leak sensor output, 0-9. 0 indicates no leak, and 9 indicates 
        that a leak is present.
T       Measurment time. Ideally this should be be the magnetometer's 
        cycling time minus 35ms, with a maximum of 965ms. If you see
        a G message, indicating that measurement was prematurely 
        terminated due to a high gradient condition, this value will
        tell you how severe the gradient is.
Q       Signal quality. This is a two-digit number between 00 to 99.
        The left digit is a good indication of signal strength, and the
        right digit indicates how much information was available
        for measurement.
!       Warning Messages.
CR      Carriage Return (ASCII code 13).
LF      Line Feed (ASCII code 10)

Warning Messages:
There are four different warning messages that can be displayed in the raw
data log by the magnetometer.

Letter  Meaning
------  -------------------------------
W       Weak signal.
G       Gradient condition. In high magnetic gradients, the signal produced
        by the sensor decays more quickly. This message occurs if the 
        measurement time was prematurely terminated due to a quickly decaying
        signal. 
P       Poor reading. This message is displayed if the signal is sampled for
        too short a time period. Expect this message under conditions of
        extremely high magnetic gradient.
M       Instrument Mistuned.




Earth total field magnetic data are collected from a surgace-towed
Marine Magnetics Seaspy Magnetometer/Gradiometer and logged on the
realtime computer.  The magnetometers can be towed in either one bottle
(magnetometer mode) or two bottle (gradiometer) configurations.

These magnetometers use the Overhauser effect to measure the earth's magnetic 
field, unlike the older Geometrics proton magnetometers.

Cable layout is as follows: A single bottle is towed with a 400 meter segment
of tow cable. If a second bottle is in use, it is towed behind the first 
bottle with an additional 100 meter segment of cable, for roughly a 500 meter
total layback from the ship.

Data is received at a 1 Hz interval, and written to a
SSMAGinpf.yyyymondd file on the realtime computer.  The actual time
interval varies, and it is best computed by using the time difference
between adjacent records. Once a day, the data is copied off of the 
real-time server over to the post-processing server for further processing.

The mag fish keep their own internal clocks which do have a tendency to drift.
The acquisition software re-syncs the time every 24 hours.

The data consist of time and magnetic total field value in nanoTesslas
(nT) from each magnetometer cycle.


Data records may be preceded by Unix timestamp.


