The measurement and recording of subsurface
water temperature at various depths is called a
bathythermograph observation. Bathythermograph
observations are normally conducted only in ocean
depths of 100 fathoms (600 feet) or greater. The
abbreviation "BT" is often used for the term
Although most bathythermograph observations are
conducted by Sonar Technicians and Aviation Warfare
Systems Operators, Aerographers Mates may conduct
these observations while deployed aboard ship with
mobile environmental teams. A far larger number of
Aerographers routinely receive and use the transmitted
observation reports to produce a variety of acoustic
analyses and forecasts for USW support and other
The input of accurate realtime
bathythermograph data is the critical factor in
determining the sound velocity profile (SVP) of a
particular ocean area.
It is from the SVP that the
presence or absence of various acoustic propagation
paths can be determined and thus exploited.
I n a d d i t i o n t o d i r e c t w a r f a r e s u p p o r t ,
bathythermograph observations are also used to analyze
the location and structure of ocean fronts and eddies.
These observations are an important input to numerical
oceanographic models that analyze and predict ocean
currents, surface temperatures, and other features.
Bathythermograph observations are also archived in
climatological data bases used by acoustic predictions
systems; they are also used by Research and
Development (R&D) activities to develop new
oceanographic and acoustic models.
To be consistent with other environmental
observations, the World Meteorological Organization
has set standard bathythetmograph observation times as
the synoptic hours0000, 0600, 1200, and 1800 UTC.
Operators should attempt to make all BT observations
as close to a synoptic hour as possible. USW ships
bathythermograph (SXBT) probes every 6 hours, but
may reduce observations to once per day when
operating within the same area for more than 24 hours.
At least one BT observation should be taken when a ship
enters an area with a differingthermal structure, such as
in the vicinity of ocean fronts, eddies, major river
outflow areas, and differing water masses.
Q4. What is the primary purpose of conducting
Q5. What are some other important uses of
Q6. When should routine BT observations be
LEARNING OBJECTIVES: Discuss the
background and history of bathythermograph
observations. Describe the basic operation and
m a i n t e n a n c e o f t h e A N / S S Q - 6 1 ( A )
bathythermograph set and the AN/BQH-7(A)
oceanographic data system.
Many different types of seawater temperature-
measuring equipment are in routine use throughout the
S h i p s a n d
bathythermograph observations using both installed
sensors and expendable bathythermograph probes.
Aircraft deploy a sonobuoy called an airborne
expendable bathythermograph (AXBT). An AXBT
measures ocean temperature during the probes transit to
the bottom and relays the information to the aircraft via
radio signals. Aircraft use different types of recorders
that will plot temperature/depth profiles. There are also
many types of moored and drifting meteorological/
oceanographic buoys that are equipped with a sensor
cable (tail) that can measure the ocean temperature at
fixed depths. The following text discusses only
shipboard bathythermograph systems.
BACKGROUND AND HISTORY
Through the late 1950s, Aerographers Mates
conducted bathythermograph observations by lowering
and recovering a cable-tethered bathythermograph
probe over the side of the ship. A carbon-covered glass
slide carried by the probe was removed and evaluated
for each observation. In the 1960s, the electronic
bathythermograph recorder AN/SSQ-56 system, using
expendable bathythermograph probes, was introduced.
Several system modifications were made over the years,
the newest of which is designated the AN/SSQ-61(A).
Beginning in late 1986, new construction surface ships
began to receive the next generation of
bathythermograph equipment, the AN/BQH-7(A)
oceanographic data system. The AN/BQH-7A, also
called a "bathythermograph/sound velocimeter," uses
the same probes used by the AN/SSQ-(series) sets, but it