8.2. MEASUREMENT TOOLS AND TECHNIQUES
471
tolerable levels. For instance, velocity measurements with a probable error
range of ±1 cm/s may be acceptable for measurement of large-scale wave
orbital velocities, but the same measurement error will not be acceptable in
a laboratory study of wave-induced turbulence. For laboratory studies that
are small-scale physical models of prototype-scale projects, it is probably
safe to agree with Kamphuis (1991) who said, “The quality of the model
output [from instruments] far exceeds the general capabilities of the model,
which are limited by scale and laboratory effects. ”
Quantifying measurement error is important in establishing the reliability of laboratory studies, but this may be difficult because part of the
variations seen in measurements may be due to factors external to the instrument. For example, repeated measurements may vary because of the
inability to repeat exactly a flow condition or because of the random nature
inherent in some flow problems (Hydraulic Laboratory Techniques 1980).
If a sufficient number of repetitive measurements can be obtained, it is possible to establish the statistical “probable range of error” of the instrument
when operated under similar conditions.
Systematic measurement errors are errors resulting from some external
factor that the investigator has the ability to control. Examples of systematic errors include incorrect instrument adjustment, fouled sensors, faulty
electrical connections, and instrument operation outside the usable range.
Systematic errors will not be revealed by statistical analysis, and the only
way to eliminate the errors is through careful and continual checking of the
instruments, experimental setup, and methodology.
8.2 Measurement Tools and Techniques
Many of the measurement tools and techniques commonly used today in
coastal engineering laboratory studies had their origins in the early years
of hydraulic modeling. Since that time, measurement capability has generally evolved as our understanding of coastal physical processes increased.
As new theories were advanced, requirements for more accurate and varied
laboratory measurements led to development of enhanced instruments and
better techniques. Fortunately, our need for better instrumentation coincided with astounding advances in the fields of electronics, computers, and
instrument design. In a true “chicken or egg” relationship, increased physical understanding led to the need for better instruments, and increased
measurement capability fostered research ideas that ultimately led to better physical understanding.
The following sections provide an overview of laboratory measurements
commonly encountered in coastal engineering studies. Brief descriptions
471
tolerable levels. For instance, velocity measurements with a probable error
range of ±1 cm/s may be acceptable for measurement of large-scale wave
orbital velocities, but the same measurement error will not be acceptable in
a laboratory study of wave-induced turbulence. For laboratory studies that
are small-scale physical models of prototype-scale projects, it is probably
safe to agree with Kamphuis (1991) who said, “The quality of the model
output [from instruments] far exceeds the general capabilities of the model,
which are limited by scale and laboratory effects. ”
Quantifying measurement error is important in establishing the reliability of laboratory studies, but this may be difficult because part of the
variations seen in measurements may be due to factors external to the instrument. For example, repeated measurements may vary because of the
inability to repeat exactly a flow condition or because of the random nature
inherent in some flow problems (Hydraulic Laboratory Techniques 1980).
If a sufficient number of repetitive measurements can be obtained, it is possible to establish the statistical “probable range of error” of the instrument
when operated under similar conditions.
Systematic measurement errors are errors resulting from some external
factor that the investigator has the ability to control. Examples of systematic errors include incorrect instrument adjustment, fouled sensors, faulty
electrical connections, and instrument operation outside the usable range.
Systematic errors will not be revealed by statistical analysis, and the only
way to eliminate the errors is through careful and continual checking of the
instruments, experimental setup, and methodology.
8.2 Measurement Tools and Techniques
Many of the measurement tools and techniques commonly used today in
coastal engineering laboratory studies had their origins in the early years
of hydraulic modeling. Since that time, measurement capability has generally evolved as our understanding of coastal physical processes increased.
As new theories were advanced, requirements for more accurate and varied
laboratory measurements led to development of enhanced instruments and
better techniques. Fortunately, our need for better instrumentation coincided with astounding advances in the fields of electronics, computers, and
instrument design. In a true “chicken or egg” relationship, increased physical understanding led to the need for better instruments, and increased
measurement capability fostered research ideas that ultimately led to better physical understanding.
The following sections provide an overview of laboratory measurements
commonly encountered in coastal engineering studies. Brief descriptions