A DATA ACQUISITION AND REDUCTION SYSTEM 
FOR OCEANOGRAPHIC MEASUREMENTS 
by DAVID D. KETCHUM and RAYMOND G, STEVENS 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 
ABSTRACT 
A system for recording and reducing 
oceanographic data in many time-dependent 
variables is described. The system permits 
recording up to twelve simultaneous data 
channels with a nominal frequency response 
from DC to 10 cycles. Transducer outputs 
are converted to FM-analog form using stan- 
dard telemetry techniques and components. 
The data multiplex is recorded on magnetic 
tape with or without an intervening tele- 
metering link. 
The tape recorded data is played back 
into an analog to digital data reduction 
system, which samples the individual chan- 
nels, converting the analog data into digital 
format suitable for entry into an electronic 
digital computer. 
The use of a standardized tape format 
and modular components in field data acqui- 
sition units assures a highly flexible 
system applicable to a wide variety of 
oceanographic and marine meteorological 
problems. 
INTRODUCTION 
One unusual feature of oceanographic 
science is the fact that the basic phenomena 
which we strive to understand are charac- 
terized by variables which are both time 
and space dependent. 
Most of the early work, and much of the 
present work, in oceanography consists of a 
spatial sampling of oceanographic parameters 
wherein observations are made from ships 
covering the wide expanse and depth of ocean. 
In many cases the time dependence of such 
data must be ignored since it cannot be 
observed. The so-called "classical" oceanog- 
raphy which has so carefully traced the 
spatial distribution of water masses and 
their chemical and thermal content falls 
into this category. However, since we know 
that the ocean is dynamic, always in motion, 
always influenced by spatial and time varying 
solar radiation, atmospheric winds and pre- 
cipitation it would seem essential to ob- 
serve the time variable characteristics of 
Woods Hole Oceanographic Institution 
Contribution No. 1227 
55 
the ocean as well as its spatial variability 
if we are to gain an understanding of its 
dynamic processes. 
Until very recently oceanographers 
have not had the technological or financial 
resources at their disposal to carry out 
extensive time dependent observations. 
However, some recent technological advances 
make possible the design of compact fast 
response transducers for the measurement 
of many physical and chemical variables. 
Another important technological advance 
is in the area of information transmission, 
storage and retrieval which provides the 
link between field observations and the 
digital computer, thus forming a unified 
system for observation and analysis of 
time varying data. 
The remainder of this paper is devoted 
to a description of one system which per- 
forms the function of information trans- 
mission, storage and retrieval. It should 
be pointed out before entering into the 
technical discussion that there are many 
subtle but important differences between 
serial time dependent observations and 
the broad scale spatial observations in 
oceanography. For example, time serial 
observations tend to accumulate vast 
quantities of data which must be handled 
by rather elaborate statistical techniques - 
thus the requirement for a digital computer 
and automatic data reduction systems. 
Furthermore it is absolutely essential 
that the dynamic characteristics of the 
entire data acquisition and reduction 
system be considered in addition to the 
more usual consideration of accuracy of 
the measuring system. In fact accuracy 
and dynamic response are inextricably 
linked when measuring time dependent 
variables. 
FUNCTIONAL DESCRIPTION 
In recognition of the need for a 
system capable of recording several simul- 
taneous channels of continuous time-depen- 
dent data with frequency components ranging 
