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PREPARING TO RUN ARTOA-II
Preparing Data for ARTOA-II
Program Pargot - now in Matlab
Option to read Argos raw data directly into ARTOA-II TWO formats?
Preparing Parameters for Tracking
Program to acquire and format header information
Program to create soso file
Before ARTOA-II can be run, information must be collected on the sound velocity in the
experiment area, and on the drifts of the clocks in the sources and floats. Usually, the program that
converts the float data from hexadecimal to "rfb" format computes the float clock drift by
comparing the float clock time to the time recorded by the Argos data system when the float
surfaces.
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Sound source clock drifts can be determined directly by recovering the instrument and comparing
its clock with standard time. They can also be computed by comparing the final TOA heard from
that source by the float (converted to travel-time) to the distance between the float's surface
location and the sound source. The accuracy of this calculation is dependent on the accuracy of the
sound velocity used. Care should be taken extrapolating the float's location back to the time of the
last TOA, as this also affects accuracy.
Another thing to consider is leap seconds – one-second adjustments that are made to keep atomic
clocks matched to astronomical time. The difference between a submerged clock (uncorrected) and
a standard clock (corrected) will be affected. All leap seconds are positive, so if a leap second has
occurred during an experiment, the difference between the two clocks should have one second
subtracted from it. The website below keeps track of leap seconds:
http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm
Sound velocity can be calculated using ray-tracing programs, or by comparing the distance
between a known float location (usually the launch location to minimize clock drifts) and source
location and the travel-time between them. To use an a priori sound speed, specify the value in the
Sound Source file select 'Sound.Source File' in the tracking-parameter window. Otherwise,
ARTOA-II can compute the sound speed by several methods:
1. Del Grosso - uses the Del Grosso equation in the Matlab routine soundspeed.m to compute
sound velocity from mean temperature and pressure (Del Grosso, 1974).
2. Linear - calculates the speed of sound by the linearized expression :
sound_velocity = (average T - 7) *0.0011 + 1.49
3. Levitus - sound velocity computed from climatological data (Boyer and Levitus, 1994;
Levitus et al., 1998) (Not implemented; defaults to 1500m/s)
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