Method, device and system for range finding

A device for use with a spool of optical fibre for range finding, wherein the device is configured to:

• determine a first optical signature of the spool of optical fibre wound in a winding pattern which comprises repeated changes in a winding parameter to provide a different optical response such that the first optical signature comprises a plurality of markers representing each change in the winding parameter;
• determine a second optical signature of the spool of optical fibre after fibre has been despooled from the spool;
• and
• calculate a length of despooled fibre based on a comparison of the first and second optical signatures.

A method of deploying optical fibre, the optical fibre wound in a winding pattern on a spool, the winding pattern comprising repeated changes in a winding parameter, the method comprising:

• determining a first optical signature of the spool of optical fibre, the first optical signature comprising a plurality of markers representing each change in the winding parameter;
• deploying the spool in a wellbore such that optical fibre despools from the spool;
• determining a second optical signature of the spool of optical fibre after deploying the spool;
• and
• calculating a length of despooled optical fibre based on a comparison of the first and second optical signatures.