Compass System Research Articles

Hippocampal ablated homing pigeons show a persistent impairment in the time taken to return home

Homing pigeons were subjected to either hippocampal or control anterior forebrain ablations to examine what role the hippocampus and related structures may play in homing behavior. One year after surgery, the test birds were released from five locations where they had never been before. Both groups were successful in orienting homeward from the release sites, indicating that the hippocampus is not necessary for the neural regulation of a pigeon's map and compass system. Nonetheless, hippocampal ablated pigeons were significantly poorer with respect to the time required to return home, indicating a homing performance impairment. Alternative hypotheses are discussed to explain this result, the most parsimonious being impaired ability on the part of the hippocampal ablated birds to direct a course homeward.

Vehicle Navigation Using the Adaptive Compass

Magnetic sensors have been used in navigation for many centuries. During this time the effects of magnetic interference from ferromagnetic materials used in vehicle construction have become an increasing problem, and correction techniques have evolved progressively to allow the continued use of magnetic heading detection. The advent of the microprocessor has made it possible to take a fresh look at the problems of compass operation in vehicles and to devise more accurate processes for the correction of the indicated heading. The compass system described in this paper uses a mathematical representation of the magnetic environment based on fundamental physical principles to supply accurate heading information even in the most magnetically hostile land vehicles.

Compasses used by birds

Birds can make use of the geomagnetic field, of the sun and the stars to find geographic directions. The magnetic compass represents an innate mechanism based on the birds' ability to perceive the earth's magnetic field while the sun compass and the star compass are learned. In the establishment of the latter, celestial rotation as well as the magnetic field have been shown to be involved. The operation modes of these compass systems and also the role of other factors known to affect birds' directional selections (e.g. sunset point, landmarks, wind etc.) are described and discussed.

Magnetic orientation in homing pigeons

Homing pigeons appear to use both a and compass system to find their way home. Under sunny skies, the sun is used as a compass. But when the sun is obscured, pigeons appear to use the earth's magnetic field. The sensory basis of the pigeon's map is unknown but the disorientation of pigeons at magnetic anomalies under sunny conditions suggests that the map may be partly based on magnetic cues. Recently small deposits of the mineral magnetite have been found in two regions of the pigeon's head. It is conceivable that this material may somehow be involved in the pigeon's sensitivity to magnetic fields.

Compass Swinging without Rotating the Aircraft

The principle of applying controlled direct current to the flux valve to simulate rotation of the aircraft in a compass swing is discussed. The validity of the technique is demonstrated for the measurement of single cycle error and the MC-1 and MC-2 are shown as implementations of this technique. Work is now in process to eliminate calibration procedures, and to extend the technique to the pilot's standby compass and to aircraft with significant soft-iron error.The precise navigation of modern aircraft requires an accurate source of heading information. In the primary mode of operation this signal is often obtained from an inertial reference, but the advent of inertial navigation has not eliminated the role of accurate magnetically slaved systems. A flux valve is often used to provide magnetic information to platform systems for use in initial alignment or in standby modes of operation and a magnetically slaved compass system, teamed with a doppler navigator, is still an excellent reference for long flights. For both applications full performance can only be obtained if the signal from the flux valve is carefully compensated in a compass swing.

A Dead-Reckoning Land Vehicle Navigation System

the dead-reckoning navigation system described, was designed to meet Canadian Army requirements for a navigation aid which would provide commanders of tracked or wheeled vehicles with continuous, accurate, positional and navigational information. The system permits vehicle movement about the battlefield under conditions of poor visibility such as in darkness, in fog or smoke and in country devoid of landmarks such as desert or arctic regions or in areas where reliable maps are not available. The, system continuously computes and displays the exact geographical location of the vehicle and the direction in which it is heading. The inputs to the land navigation system are: distance; travelled by the vehicle as measured by an odometer drive, and direction of travel obtained from a true north seeking gyro compass. The complete system consists of a Computer, Heading and Position Indicator, Vehicle Position Plotter, Heading Indicator, Gyro Compass and Power Supply. The Computer employs a unique and highly accurate mechanical analogue computing element (Ball Resolver) to convert inputs representing distance and direction of travel into electrical output pulses which represent the East/West and North/South movement of the vehicle. The commander's Heading and Position Indicator displays the computer outputs (vehicle position) as two four digit map references, and a 0–360° dial continuously indicates the grid heading of the vehicle. The Vehicle Position Plotter provides a continuous pictorial representation of the geographical location of the vehicle and the direction in which it is headed. An illuminated image of a positional dot and directional arrow is projected onto the underside of a standard military map attached to the top of the Plotter. This display enables the navigator to pictorially steer the vehicle along any prescribed course without manual plotting or mental calculations. The Heading Indicator, necessary only in vehicles where the driver is separated from the commander, continuously displays vehicle heading and can be used as a steering aid for a prescribed heading. The system operates from the vehicle battery and employs a static inverter to obtain the alternating current required by the Compass and other systems units. The land vehicle navigation meets the accuracy requirements of 1% of distance travelled.

Testing a Modern Gyro-Magnetic Compass

Gyro magnetic compasses are subject to a large number of errors, some of which may be eliminated, or at least greatly reduced, by careful design on the part of the instrument manufacturer and an intelligent operating drill on the part of the user. Table I shows errors under five basic headings, and allots to each error a symbol classifying it as:(a) The responsibility of the instrument manufacturer (I)(b) The responsibility of the aircraft manufacturer or its operator (A)(c) Inadequate knowledge of the geomagnetic structure of the Earth's field (K)Some sources of error in Table I are marked with an asterisk. It is these which the designers of the compass system described have endeavoured to eliminate.

Aviation Electronics

Details of Electrical and Electronic Apparatus with Applications in the Maintenance and Operation of Aircraft, Missiles and Space Vehicles. The latest addition to the range of high performance gyroscopic flight instrumentation made by Fcrranti Ltd. for modern aircraft applications is a lightweight compass system.

TV Borehole Camera--A Visual Approach to Geophysical Logging: ABSTRACT

In recent years, miniaturization of electronic components has led to development of seeing-eye TV cameras capable of entering small-diameter boreholes. Commercially available cameras now can operate in 3-inch holes to depths exceeding 5,000 feet. Some cameras look downhole; others view sideward by means of rotating mirrors. Built-in compass systems permit accurate surveys of hole orientation and attitudes of planar elements intersecting the borehole. End_Page 370------------------------------ TV borehole cameras have many geological and engineering applications. In dry uncased holes, uses include determination of lithologic character and stratigraphic contacts, measurement of bedding and fracture orientation, identification of textural features (porosities), and establishment of causes of drilling problems including recognition of caved zones and intervals of circulation loss. A TV camera survey supplements or replaces coring. If hole walls are clean, inspection of the entire interval provides direct information normally lost where core recovery is poor. In holes containing buckled or perforated casing, lost tools or unknown obstructions, a TV traverse may guide the driller to an effective, time-and cost-saving remedy. The Lawrence Radiation Laboratory has built two cameras for use in pre- and post-shot studies associated with underground nuclear explosions. These 2½-inch diameter cameras can reach 3,000-foot depths and will operate in vertical or inclined holes up to diameters limited only by illumination capability. Both cameras have remote-control focussing. One camera, having a fixed side-viewing mirror, is equipped with a specially designed compass. The other camera looks down the axis of the hole. Field experience with these cameras is described and photos of the monitor image illustrate the results obtainable during in-hole operation. TV pictures showing the Gnome explosion cavity are compared with actual photographs taken inside this void. The current status of TV borehole camera technology and possible future developments in both instrumentation and applications are reviewed. End_of_Article - Last_Page 371------------

Use of a Doppler Navigation System and Fixes to Monitor Aircraft Heading

When trials of civil aircraft doppler navigation systems are carried out over land the pattern of results generally show a small along-track error component and a large across-track error component, whereas when the basic doppler radar is assessed, the errors over land are about ±0·2 per cent of distance gone and ±0°.2 in drift (standard deviation). It is not possible to quote system errors for all permutations of doppler equipments and compass systems but it is suggested that a good working figure for the across-track system error component would be about ±3 per cent (standard deviation), i.e. a compass error of ±1°.7. Advantage can be taken of the inherent accuracy of the doppler radar equipment to determine the heading error from a knowledge of track made good and the mean doppler drift along that track.The standard twin-channel civil doppler navigation computer combines aircraft heading with doppler drift and doppler distance gone to form a ‘computer track’ in coordinates of distance along and across a preset track and distance. The computer is, in effect, meaning the doppler drift between selected points and adding this value to an arbitrary datum (aircraft compass) to form the computer track. If we can determine the true track over the ground we can assume that the error between computer track and actual track is caused entirely by error in the arbitrary datum, i.e. heading error.

Rictometer System for Calibrating Transmitters of Remote Indicating Compasses

Calibration of the sensor (transmitter), of a remote indicating compass system, must be carried out in a magnetic field whose magnitude and direction simulate closely those of the earth at a specified point. Major disturbances of the earth's magnetic field by electrical equipment occur in most laboratories. Where conventional Helmholtz calibrating schemes are used, accuracy can be achieved only by lengthy averaging of repeated measurements and exercising extreme care. This paper describes a measurement system called a rictometer, which permits precise transmitter calibration with much greater ease than previously. The rictometer consists of a system of shields which reduces the earth's horizontal field component from 200 milligauss to about 13 of a milligauss. Two pairs of Helmholtz coils within the shielding system restore the horizontal component of the earth's field. By proper selection of currents in each of these pairs of coils,this horizontal component can be rotated in discrete steps through 360° for calibration purposes. The rictometer allows the experimenter to calibrate a compass transmitter readily with a precision of plus or minus 0.1 deg in normal laboratory fields. Deliberate immersion of the rictometer in a 50 gauss field causes a maximum transmitter calibration change of plus or minus 0.15°. Thus, the system should prove valuable for reliable sensor calibration under most adverse field conditions.

Heading Definition in Commercial Aircraft

In this paper, methods of defining heading are enumerated and the limitations of magnetic and gyroscopic devices are analysed in detail. Particular attention is paid to the development of the rotated race principle which is likely to be responsible for a large improvement in the basic azimuth gyro. The gyro-magnetic combination is scrutinized and the errors inherent in this compass system are classified. The possibility and consequent effect of diminishing certain categories of error are presented. The current position is summarized and an attempt is made to suggest possible future trends. The authors are, respectively, with Smiths Aircraft Instruments and the Sperry Gyroscope Company.

Aeroplane Compass

IN Sky and Telescope of January 1944 there is a description of the Gyro Flux Gate Compass System, which has overcome many difficulties for air navigators. It combines the action of the flux of the earth's magnetic field with a gyroscope designed to keep it horizontal in spite of the movements of the aeroplane. It is very much more sensitive than the ordinary compass, and it can be operated close to the earth's magnetic poles, if necessary. The existence of the instrument has been revealed recently, because it is believed that some of the compasses have fallen into the hands of the enemy, though it seems certain that he cannot produce it in great quantity during the present War. A description of the instrument is given; but the technical details are too complicated to be dealt with here. Its practical utility can be judged from the fact that its reading of true compass directions and its reliability under varying conditions have contributed to reduce the number of accidents due to uncertainties in navigation.