306
9 Experimental Methods in Fluid Mechanics
variables that need to be considered can be reduced by combining physical
variables into dimensionless products. A rational procedure which forms the
dimensionless products is known as dimensional analysis.
Experimental data on many ocean physical parameters reflect their random
character. Therefore, special techniques are required to process these data. At
the end of this chapter, a brief review of the most important statistical and
spectral techniques in application to ocean data is given.
9.2 Field and Laboratory Measurement Techniques
There are many various instruments, types of observations and methods of
analysis developed in fluid mechanics and oceanography which have undergone considerable change over the last few decades. A very comprehensive and
practical compilation of the essential information on instrumentation and data
analysis was recently published by Emery and Thomson (1997). The description of older types of instrumentation is provided in many books on physical
oceanography (see, for example, von Arx, 1977). Therefore, in this book we
only briefly describe the most important measurement methods and data analysis techniques.
9.2.1 Temperature
During the world's first oceanographic expedition (1872-1874), the Challenger
investigators made observations at 362 locations taking tens of thousand of
samples of the Atlantic and Pacific oceans. At each sampled depth, a temperature reading was made by breaking the capillary column in a bulb thermometer
by remote control. For the next 90 years this time-consuming method of temperature measurement prevailed, with only modest improvements. Although
this method is good for establishing the seasonal variations of sea-water temperature at various depths, its sampling accuracy is far too coarse to detect
small-scale changes in temperature.
At present, there are a few methods for measurement of the ocean temperature. They include convenient mercury thermometers, simple and reversing,
and more sophisticated bathythermographs and temperature profilers. Special methods have been developed to measure the sea surface temperature
(SST). Here we will describe the principle of temperature measurement using bathythermographs and profilers. Measurement of sea surface temperature
is described in the next section.
In the expendable bathythermograph (XBT), the dependence of a metal's electrical resistance on temperature is used. The XBT is a free-falling probe which
provides an upper ocean temperature profile. The most commonly used metals
are copper, platinum and nickel. For example, platinum thermometers have
accuracies of ±0.00l DC. Another class of resistive materials used for temperature measurements are semiconductors, known in oceanographic applications
as thermistors, which have some advantages over metal due to their higher
9 Experimental Methods in Fluid Mechanics
variables that need to be considered can be reduced by combining physical
variables into dimensionless products. A rational procedure which forms the
dimensionless products is known as dimensional analysis.
Experimental data on many ocean physical parameters reflect their random
character. Therefore, special techniques are required to process these data. At
the end of this chapter, a brief review of the most important statistical and
spectral techniques in application to ocean data is given.
9.2 Field and Laboratory Measurement Techniques
There are many various instruments, types of observations and methods of
analysis developed in fluid mechanics and oceanography which have undergone considerable change over the last few decades. A very comprehensive and
practical compilation of the essential information on instrumentation and data
analysis was recently published by Emery and Thomson (1997). The description of older types of instrumentation is provided in many books on physical
oceanography (see, for example, von Arx, 1977). Therefore, in this book we
only briefly describe the most important measurement methods and data analysis techniques.
9.2.1 Temperature
During the world's first oceanographic expedition (1872-1874), the Challenger
investigators made observations at 362 locations taking tens of thousand of
samples of the Atlantic and Pacific oceans. At each sampled depth, a temperature reading was made by breaking the capillary column in a bulb thermometer
by remote control. For the next 90 years this time-consuming method of temperature measurement prevailed, with only modest improvements. Although
this method is good for establishing the seasonal variations of sea-water temperature at various depths, its sampling accuracy is far too coarse to detect
small-scale changes in temperature.
At present, there are a few methods for measurement of the ocean temperature. They include convenient mercury thermometers, simple and reversing,
and more sophisticated bathythermographs and temperature profilers. Special methods have been developed to measure the sea surface temperature
(SST). Here we will describe the principle of temperature measurement using bathythermographs and profilers. Measurement of sea surface temperature
is described in the next section.
In the expendable bathythermograph (XBT), the dependence of a metal's electrical resistance on temperature is used. The XBT is a free-falling probe which
provides an upper ocean temperature profile. The most commonly used metals
are copper, platinum and nickel. For example, platinum thermometers have
accuracies of ±0.00l DC. Another class of resistive materials used for temperature measurements are semiconductors, known in oceanographic applications
as thermistors, which have some advantages over metal due to their higher