Patent ID: 11920962
Assignee: NEC CORPORATION
Field: Measurement (Instruments)
Classification: CPC G  H | IPC G  H

Claim 15:
16. A surveying method comprising:
providing a cable including a first optical fiber in which a partial reflection unit that partially reflects a monitoring light is provided on a path so that the cable has friction with the ground, the cable being provided in such a way that the first optical fiber is expanded and contracted in accordance with a movement of the ground;
outputting the monitoring light to the first optical fiber;
receiving a reflection light reflected by the partial reflection unit; and
measuring the length of the first optical fiber to the partial reflection unit based on a round-trip propagation time of the reflection light that has been received and monitoring its changes over time, wherein
a plurality of partial reflection units are provided at different respective points of the first optical fiber,
the movement of the ground based on a fluctuation in the length of the first optical fiber between two of the plurality of partial reflection units is monitored,
a fixing member for adding a grip force to the ground is provided in the cable, and
a mirror transponder used for echo ranging in the sea, the mirror transponder outputting a response acoustic signal upon receiving an acoustic signal, is fixed to the fixing member.