CHAPTER 2
BATHYTHERMOGRAPH OBSERVATIONS
INTRODUCTION
In this chapter, we briefly review the basic
properties that affect sound in seawater. We then
discuss the various uses of bathythermograph data and
the equipment used to obtain this data, particularly the
AN/SSQ-61(A) bathythermograph set and the
AN/BQH-7(A) oceanographic data system. Next, we
discuss the evaluation of the bathythermograph trace.
W e e x p l a i n h o w t o u s e t h e i n t e r n a t i o n a l
bathythermograph observation reporting code and also
cover the disposition of observation records. We then
complete the chapter by explaining how to decode
messages received from drifting environmental buoys,
another valuable source of oceanographic data.
SEAWATER TRAITS AND
DEFINITIONS
LEARNING OBJECTIVE: Identify the three
basic properties of ocean water on which
sound-path predictions are based.
Undersea Warfare (USW), which involves the
detection and prosecution of hostile submarines, is one
of the largest and most important missions of the U.S.
Navy. One of the key factors that enable U.S. Navy
submarines, surface ships, and aircraft to detect hostile
submarines is our ability to predict the propagation path
of sound in the ocean waters. This same knowledge also
helps our submarines avoid detection by hostile ships
and aircraft. Sound-path predictions are based on
measurements of salinity, temperature, and depth in the
ocean waters.
SALINITY
Salinity changes in deep ocean areas occur so
slowly that we may, in most cases, consider salinity a
constant. Salinity measurements in each ocean have
been determined by oceanographic research ships and
are available in many data bases.
Salinity
measurements are not routinely needed or made by
operational ships.
TEMPERATURE
Temperature is by far the most important factor in
determining sound propagation paths in the upper
layers of the ocean. Surface and intermediate ocean-
depth temperatures change more rapidly than in deep
water, with the faster changes occurring at the surface.
Hourly satellite observations allow all significant
changes in sea surface temperature to be routinely
monitored. However, significant changes in water
temperature near the surface and at intermediate depths
require ships and aircraft to routinely measure these
temperatures at depths of up to 6,000 feet. Deep ocean
waters change temperature so slowly that routine
measurements are not required. Accurate data is
available from oceanographic data bases that are
updated by research ships and other sources.
OCEAN DEPTH
Ocean depth is also important to USW operations
since the pressure of seawater is the dominant factor
affecting sound velocity in the deep layers of the ocean.
Ocean depth also affects sound propagation paths, such
as bottom bounce and convergence zone.
REVIEW QUESTIONS
Q1. What property affecting sound propagation in
seawater is normally considered a constant?
Q2. What is the most important factor affecting
sound propagation in the upper layers of the
ocean?
Q3. What is the dominant factor affecting sound
speed in deep ocean layers?
USE OF BATHYTHERMOGRAPH
OBSERVATIONS
LEARNING OBJECTIVES: Identify the main
uses of bathythermograph data. Identify when
bathythermograph observations are conducted.
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