Missing Standards
3.1 / File format for Brillouin sensing
Having a standardised file format would allow the interoperability between different equipment and manufacturers.
The file should contain all information that influence the value of the numerical data acquired, so that to allow the user to process the data in order to compensate for changes in wavelength, power and resolution.
An important element that is at present totally neglected is the wavelength of the Brillouin pump that is used for the analysis.
In fact, for a step-index fibre, the Brillouin frequency shift depends on refractive index, pump wavelength and acoustic velocity and can be calculated from Equation 1.
This translates is a strict dependency of the Brillouin shift from the pump wavelength, consequently the actual pump wavelength should be given in each data file with an accuracy that matches the strain/temperature resolution claimed for the interrogator.
For example, considering a standard SMF-28 sensing fibre (n = 1.4682 and Va=5747.669 m/s), a change of only 0.018 nm (18pm) of the pump wavelength from the nominal 1552.000 nm value could cause the same 125 kHz Brillouin shift of a temperature change equal to an instrument resolution of 0.1°C (considering a temperature coefficient of 1.2 MHz/°C); and a change of only 0.014 nm (15 pm) could cause the same 100 kHz Brillouin shift of a temperature change equal to an instrument resolution of 10me (considering a strain coefficient of 500 MHz/%).
It is therefore suggested to embed a suitable wavelength measurement system in the equipment hardware so that to provide the value of the pump wavelength with an accuracy at least two times better than the temperature/strain accuracy claimed for the interrogator equipment.
3.2 / File formats for equipment measurement configuration
Having a standardised file format would allow the interoperability between different equipment and manufacturers.
3.3 / Control protocols for equipment
Having a standardised file format would allow the interoperability between different equipment and manufacturers for the integration into an automated centralized control system.
3.4 / Data sheets for sensing cables:
3.4.1 / Strain cable
Providing the information needed by the installer in order to correctly select the cable that matches the interrogator performance and the needs of a specific intallation
3.4.2 / Temperature cable
Providing the information needed by the installer in order to correctly select the cable that matches the interrogator performance and the needs of a specific installation
