Apparatus for detecting changes of a medium along a measuring path in the medium, comprising several lightwave conductors arranged on a carrier, conveniently in a sleeve. Reflective ends of the light wave conductors are fixed at different distances along the measuring path. Type, extent, and location of longitudinal changes in the medium to be checked can be detected at any time by optical length measuring of the individual lightwave conductors by means of an optical rangefinder.

An improved ship which incorporates a distortion sensor arrangement. Measurement data supplied by the distortion sensor arrangement is preferably used to correct measurement data supplied by and/or control signals for an on-board directional apparatus. The distortion sensor arrangement preferably includes a hull-mounted laser beam/light sensor combination, and such that the light sensor continuously measures a deflection of the laser beam in response to a distortion of the ship.

A position, orientation, shape and motion measuring tool is provided in the form of a flexible substrate with bend and twist sensors distributed along its surface at known intervals. A ribbon-type substrate is preferred. The geometric configuration of the substrate is calculated from inter-referencing the locations and orientations of the sensors based upon the detected bend and twist values. Suitable applications include motion capture for humans for use in animation, six degree of freedom input to a computer, profile measurement and location tracking within a large, singularity-free working space.

For continuous monitoring of dynamic loads, including stresses and strains in large hull structures for vessels (5), a strain measurement system (2) is employed with fiber optic cables which connect optical strain sensors (7; 16) at different points in the hull structure. Optical signals for detection of stresses and strains are distributed to the strain sensors (7; 16) from an optical transmitter (11). The strain measurement system (2) is connected via a central monitoring unit (10) to a computer-implemented control system (1) which in turn is connected to a display and data presentation unit (4) and possibly other measurement systems (3). In a first operating mode, strain values during loading and unloading of the vessel (5) are detected by the strain sensors (7; 16). The control system (1) generates a curve which shows an average strain, and an alarm signal if the average strain exceeds a predetermined threshold which indicates an unacceptable level of strain. In a second operating mode, when the vessel (5) is underway, strains are continuously detected by the strain sensors (7; 16). An alarm signal is generated if the average strain exceeds a predetermined threshold which indicates an unacceptable level of strain. A strain measurement system and a fiber optic strain sensor (16) are also used with this method.

A method of measuring structural defects of a structure including the steps of: a) attaching to the structure at least one structural defect sensor each including a fibre optic cable in turn including a plurality of longitudinally extending optical fibres mounted in a predetermined spaced apart substantially parallel co-planar array, selected fibres having Bragg Gratings located along their length in their surfaces, one side of the array being adapted for attachment to a surface of a structure to be tested, b) coupling to one end of the fibre optic cable of each sensor a light source, and an optical sensor having time domain measuring and multiplexing capabilities, and, c) monitoring a variation of a light parameter measured by the optical detector using time domain measurement to locate the position of a crack along a fibre and using multiplexing for determining from which fibre the light source is being analyzed, and d) monitoring point strains by measuring a characteristic of light reflected from the Bragg Gratings.