Abstract: Primarily (but not exclusively) in the field of natural resources exploration, there is a requirement to measure the absolute value and variation of gravity at a given point and over an area gradient, thereby detecting the presence of sub-surface anomalies which give rise to the variation in the measured gravity value. In order to provide a portable, accurate, efficient and cost effective method for making the measurements, a gravity sensing apparatus (ABCD) can be deployed using a variety of vehicles, such as (for example, but not limited to) an aircraft or helicopter, with compensation applied by a motion sensing apparatus (EFGH) to reduce or eliminate the effects of vibration and vehicle motion and structural flexure on the gravity and gravity gradiometry data.

Abstract: Primarily (but not exclusively) in the field of natural resources exploration, there is a requirement to measure the absolute value and variation of gravity at a given point and over an area gradient, thereby detecting the presence of sub-surface anomalies which give rise to the variation in the measured gravity value. In order to provide a portable, accurate, efficient and cost effective method for making the measurements, a gravity sensing apparatus (ABCD) can be deployed using a variety of vehicles, such as (for example, but not limited to) an aircraft or helicopter, with compensation applied by a motion sensing apparatus (EFGH) to reduce or eliminate the effects of vibration and vehicle motion and structural flexure on the gravity and gravity gradiometry data.

Abstract: Apparatus for determining the velocity and direction of a moving object, the apparatus comprising: a coherent light (L) source arranged to generate an incident beam (B) of coherent light; an optical imaging system arranged to receive light reflected from a moving object passing through the incident beam and to focus the reflected light into a magnified image of the moving image; a first optical mask (M) through which the magnified image is projected, the mask having a first region of alternating opaque and non-opaque areas having a first spacing and second region of alternating opaque and non-opaque areas having a second spacing different from the first spacing; a first light detector (D) arranged to receive the light signal transmitted through the optical mask, the light signal comprising a series of pulses, and to calculate the velocity and direction of the moving object as a function of the pulse frequency and the spacing of the opaque areas of the optical mask.

Abstract: A position detector for detecting the position of a helicopter blade includes a sensor to generate a signal in dependence on the position of a helicopter blade with respect to the sensor, and a data processing module arranged to receive the signal from the sensor and generate an output indicative of the blade position from the received signal. The sensor includes a mask having a plurality of slits, a lens assembly, and light detector. The lens assembly has a field of view and directs incident light onto a focal plane of the lens assembly. The light detector detects the level of illumination passing through each of the slits in the mask and provides a signal indicative of the illumination level to the data processing module. The mask is located at the focal plane of the lens assembly and the slits formed in the mask are angularly divergent from one another.

Abstract: A method of detecting the velocity of a moving object comprising the steps of: passing a beam of coherent light through an optical mask having a pattern of alternating opaque and non-opaque regions formed thereon, whereby an image of alternating light and dark fringes is projected along the length of the light beam; causing the moving object to pass through the projected image such that a portion of the light beam is reflected from the moving object as a series of pulses; detecting the reflected light pulses and the frequency of the pulses; and calculating the velocity of the object as a function of the pulse frequency and the known separation of the fringes of the image.

Abstract: A detector for checking the symmetry of a helicopter rotor while it is rotating has a scanner (11) which scans vertically a field of view (15) and the view is interrupted by a vertical strip on the blade tip (16). A slot (18) in the strip gives a characteristic signal as at (L.sub.2). The position of the signal (L.sub.2) in a scanning cycle gives an indication of the height of the blade tip and also the circumferential spacing between blades.

Abstract: A detector for checking the symmetry of a helicopter rotor while it is rotating has a scanner (11) which scans vertically a field of view (15) and the view is interrupted by a vertical strip on the blade tip (16). A slot (18) in the strip gives a characteristic signal as at (L.sub.2). The position of the signal (L.sub.2) in a scanning cycle gives an indication of the height of the blade tip and also the circumferential spacing between blades.