Four key criteria

• Measurement resolution (determines system performance, temporal resolution )
• Spatial resolution
• Measurement range –> can adjust through data acquisition setup.
• Measurement time(AKA temporal resolution)

They have close relationship. not independent

Measurement Resolution

It means how small the physical quantity changes that the sensor can measure.

resolution \(\approx\) sensitivity \(\ne\) accuracy

Measurement Range

It is usually determined by the length of fiber.

Spatial resolution

spatial resolution is \(\delta z\) in this figure. From 10% to 90% amplitude.

the hot-spot’s relative size to the resolution.

• Solid line is actual measurement
• Broken line is detected by the sensor.

Measurement time

DFOS will emit thousands of pulse in a second. DTS and DSS couldn’t return accurate result with a single pulse, average pulse up = measurement time up.

The time taken by the system to acquire the readings for all points in the sensing fiber to required measured resolution.

Short fiber vs Long fibre

A short fiber will enable the interrogator to inject more pulse. Thus it has higher measurement resolution if the measurement time is same.

5km fiber & 1s measurement time = 10km fiber & 2s measurement time in measurement resolution theoretically.

Interference in the fiber

a longer fiber will gain more information than a shorter fiber while there exists lots of pluses.

Spatial resolution and sampling resolution

• sampling resolution: determined by the acquisition system.
• Actually in the first figure, the horizontal interval of “x” mark could be regarded as sampling resolution.

backscatter: 後向散射

Interplay between performance criteria

• Higher backscatter energy -> higher measurement sensitivity
• Longer distance -> lower backscatter energy
• Longer fiber -> lower pulse frequency -> lower averaging number => lower measurement sensitivity
• Lower pulse width -> higher backscatter energy -> lower spatial resolution
• Longer measurement time -> higher measurement sensitivity -> lower temporal resolution