USE OF THE PRECISION GRAPHIC RECORDER (PGR) IN OCEANOGRAPHY 
by S.T. KNOTT, Research Associate in Engineering 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 
ABSTRACT 
This paper briefly describes the Precision 
Graphic Recorder. How its timing and correla- 
tion capabilities are used for collecting acousti- 
cally derived data in bathymetry, seismic 
reflection and refraction profiling, instrument 
location, navigation and various biological 
studies is reviewed. 
INTRODUCTION 
The roots of the name "graphic recorder" 
are found in early bathymetric work, such as 
that of Veatch and Smith! , in the 1930's. The 
PGR2, however, might better be described as 
an event correlation recorder, although its 
presentation is substantially the same as that 
of recorders in modern echo-sounders where 
a recording stylus repeatedly sweeps across 
a long narrow strip of sensitized paper. It is 
similar, also, to a delay-triggered 'Z'' axis 
modulated oscilloscope, but presents successive 
samples of time-related data side-by-side for 
visual correlation. Such a series of samples, 
each taken at a precise repetition rate ona 
common, accurate time-base, produces a 
graphic plot of the data as a succession of offset 
measurements in time. 
Prior to 1954 when Luskin et al? 
discussed the precision measurement of ocean 
depths, the geophysical research groups at the 
Woods Hole Oceanographic Institution and the 
Lamont Geological Observatory had found 
commercially available echo- sounding recorders 
to be less precise than was required for their 
problems, Nor was there an adequate choice 
of recording resolution available in one 
instrument. Both laboratories decided to 
develop instruments, and a healthy scientific 
competition evolved. Lamont's instrument, 
the Precision Depth Recorder (PDR), was 
first in the field. It provides recording 
resolutions of about 25 and 50 milliseconds per 
inch for travel time measurement on a time 
base controlled to better than 1 part in 109, 
Our recorder appeared about six months later, 
The group at Lamont Observatory conceived 
a reliable and moderately simple device for 
the measurement of ocean depths. Our record- 
er was somewhat more complicated because 
our objective was a multipurpose tool, Like 
the PDR, the PGR measures travel-times 
precisely and with predictable accuracy, but 
in addition it provides considerably higher 
resolution for a finer measure of time 
differences. From its twelve writing rates we 
obtain recording resolution from 3 milliseconds 
to 400 milliseconds per inch*, Some ten 
programing arrangements are available to 
gate the transmission and reception of signals. 
Its frequency response is flat from less than 
100 cycles to over 20 kilocycles per second, 
and its usefulness extends to beyond 80 kilo- 
cycles. Both research groups found facsimile 
recorders most useful; Lamont uses the Times 
Facsimile recorder, and we, the Alden, 
A tuning fork in the PGR establishes the 
time base, Its signal controls the synchronous 
drive of the sweep mechanism and programing 
switches. The sweep, generated by the inter- 
section of a rotating helix and a straight 
printing blade is sharply defined and rectilinear, 
with a timing accuracy of the order of the fork. 
Signals appear as a darkening on the paper 
between the helix and blade and must be 
rectified before recording because the marks 
are caused by an electrolytic deposition of 
Superior numbers refer to similarly numbered references at the end of this paper. 
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