An waveguide on access tube (WOAT) system measures soil moisture by sensors placed at various depths of a medium, such as soil. The WOAT system includes a rigid tube into which an inflatable tube with various sensors bonded to it is inserted. Once in place, the rigid tube is removed and the inflatable tube and its sensor are inflated to the diameter of the hole or channel in which it is positioned. The ability to inflate the inflatable tube allows for the sensors on the inflatable tube to be force fit against the interior wall of the hole or channel for proper soil or ambient environment measurements.

A system for detecting an intrusion of at least one of a monitoring fiber and a detector comprises a sensor having a closure monitor and an intrusion monitor, the closure monitor including a signal generator and at least one detector attached to the monitoring fiber. The signal generator transmits signal light such that the monitoring fiber receives the transmitted signal light and reflects a portion of the signal light via the at least one detector to the closure monitor and transmits a non-reflected portion of the signal light. The intrusion monitor receives the transmitted non-reflected portion of the signal light, and monitors the non-reflected portion of the signal light to detect transient changes in the non-reflected portion of the signal light indicative of at least one of a vibration, a motion and a handling of at least one of the monitoring fiber and the at least one detector.

A system for detecting an intrusion of at least one of a monitoring fiber and a detector comprises a sensor having a closure monitor and an intrusion monitor, the closure monitor including a signal generator and at least one detector attached to the monitoring fiber. The signal generator transmits signal light such that the monitoring fiber receives the transmitted signal light and reflects a portion of the signal light via the at least one detector to the closure monitor and transmits a non-reflected portion of the signal light. The intrusion monitor receives the transmitted non-reflected portion of the signal light, and monitors the non-reflected portion of the signal light to detect transient changes in the non-reflected portion of the signal light indicative of at least one of a vibration, a motion and a handling of at least one of the monitoring fiber and the at least one detector.

A method of high rate fiber optical distributed acoustic sensing includes injecting a first coherent light pattern comprising first light into an optical cable, the optical cable having at least a first reflector pair and a second reflector pair arranged at different positions along the optical cable; injecting a second coherent light pattern comprising second light into the optical cable while first backscatter light of the first light pattern is propagating in the optical cable; detecting first reflected light originating from reflection of the first light pattern from the first reflector pair and/or the second reflector pair; and, at a different interval in time: detecting second reflected light originating from reflection of the second light pattern from the first reflector pair and/or the second reflector pair.

A sensor system for detection and localisation of changes in or values for at least one environmental condition comprises a source of pulses of electromagnetic radiation, wherein the source is configured to emit electromagnetic radiation at a plurality of different wavelengths, an optical fibre in optical communication with the source of pulses, wherein said optical fibre includes one or more fibre Bragg gratings having a reflectance and/or transmittance which varies in dependence on the at least one environmental condition, and a detection unit for detecting, at a plurality of different times, electromagnetic radiation which has been reflected or transmitted by at least one of the fibre Bragg gratings, wherein the detection unit is configured for detecting electromagnetic radiation at the plurality of different wavelengths, such that a spectral response can be determined for different spatial regions along the optical fibre, wherein a change in or value for the environmental condition at a spatial region may be determined by monitoring the respective spectral response.

An optical shape sensing method is provided. The method comprises: providing first and second optical fibre portions arranged to receive light from at least one common lasers such that a path length of the light from the laser to the first optical fibre portion differs from a path length of the light from the lasers to the second optical fibre portion by a first distance; wherein the first and second optical fibre portions are spaced apart from each other in a first direction; and wherein the first and second optical fibre portions comprise a plurality of reflectors spaced along the length of the optical fibre portions, wherein the reflectors are arranged in sets of reflectors, each set including one reflector from each of the optical fibre portions, wherein the reflectors in each set are aligned with one another in a second direction that is perpendicular to the first direction when the optical fibre portions are in neutral positions; supplying light from the laser to the optical fibre portions; detecting an interferometric signal from the optical fibre portions at a common detector; determining, for each set of reflectors, optical path length differences between the reflectors in the set of reflectors based on the detected interferometric signal; determining a curvature of the optical fibre portions in the first direction based on the optical path length differences, between the reflectors in the first and second optical fibre portions, for the sets of reflectors. An optical shape sensor and optical shape sensing system are also provided.

Distributed optical fibre sensor measures vibration, as a concurrent function of position along each of a plurality of sensing optical fibres, from properties of probe light backscattered within the sensing optical fibres. The sensor includes a light-pulse-generating probe light source, a detector, an optical switch. The sensor is arranged to control the optical switch such that all of the sensing optical fibres can be used concurrently to detect acoustic vibration, and an analyser is arranged to determine vibration, as a concurrent function of position along each of the sensing optical fibres, from the detected backscattered probe light.

A distributed sensing optical fiber cable is proposed. An optical fiber is positioned at the center of the cable and includes a core region, at least one cladding layer surrounding the core region, a protective coating covering the at least one cladding layer, and a tight buffer of elastomeric thermoplastic material disposed to surround the protective coating. The remainder of the cable structure includes a pair of strength members disposed longitudinally on either side of the optical fiber (the strength members formed of a glass-based, memory-less material) and a hard plastic jacket formed to encase the optical fiber and the pair of strength members, the plastic jacket preferably exhibiting an essentially rectangular profile.

A signal detecting device includes a multiplier that multiplies a measurement signal by a reference signal, a filter that filters a multiplication result from the multiplier, a first storage that stores an internal state of the filter; and a second storage that stores a filtering result from the filter. The filter filters the multiplication result using the internal state stored in the first storage. The first storage switches an area in or from which the filter writes or reads the internal state in accordance with an index signal representing a type of amplitude of a time-divisional signal in the measurement signal. The second storage switches an area in which the filtering result is stored in accordance with the index signal.

The invention relates to a method for determining temperature changes of an optical fibre (250) having Fiber Bragg Grating (FBG) patterns provided in at least one portion (Portion 1) of said optical fibre (250), said optical fibre (250) being connected between a first detector arrangement (210) and a second detector arrangement (220), the method comprising the steps of:

emitting (s410) light into said optical fibre (250) in a first direction (D1) from said first detector arrangement (210), receiving reflections from said (FBG) patterns of such emitted light by said first detector arrangement (210), and processing said reflections for determining a current temperature change related to said optical fibre (250);

on the basis of predetermined criteria, emitting (s440) light into said optical fibre (250) in an opposite, second, direction (D2) from said second detector arrangement (220), receiving reflections from said (FBG) patterns of such emitted light by said second detector arrangement (220), and processing said reflections for determining a current temperature change related to said optical fibre (250).

The invention relates also to a computer program product comprising program code (P) for a computer (233; 243; 253; 500) for implementing a method according to the invention. The invention relates also to a system (289) for determining temperature changes of an optical fibre (250). The invention also relates to a platform (100) being equipped with the system (289).