The aircraft's velocity is measured from the Doppler shift of the transmissions or from a sequence of position measurements.dr gemson, IIAEM, JU, Bangalore34
dr gemson, IIAEM, JU, Bangalore35All these systems depend on the properties of rectilinear propagation and constant velocity of electromagnetic waves and the navigational parameters (direction, distance, etc.) are obtained by direct or indirect measurement of delay (or delays) occurring in the transmission. The positional information is related principally to i)the measurement of direction, ii)the measurement of distance, or iii)the difference in distance of two transmitters.
dr gemson, IIAEM, JU, Bangalore36These give the locus of the craft on i)a line, ii)a circle, and iii)a hyperbola, respectively. The intersection of two or more such loci gives the fix or position of the craft.
dr gemson, IIAEM, JU, Bangalore37Satellite navigation systemsThis type of navigation system also depend on the establishing of loci on which the craft is located. The Transit system, the operation of which depends upon the measurement of oDoppler shift in the frequency it radiates, odefines a hyperboloid of revolution, othe intersection of which with the surface of the earth gives the locus of the possible positions of the receiver, and othe intersection of two or more loci establishes the position of the receiver.
dr gemson, IIAEM, JU, Bangalore38India is in the process of establishing its own satellite navigation system IRNSS.
dr gemson, IIAEM, JU, Bangalore39Dead-reckoning navigation systems derive their state vector from a continuous series of measurements relative to an initial position. There are two ways of dead-reckoning measurements:Aircraft heading and either speed or acceleration. For example, heading can be measured with gyroscopes or magnetic compasses, while speed can be measured with air-data sensors or Doppler radars or Vector acceleration is measured with inertial sensorsMeasuring the emissions from continuous-wave radio stations. They create ambiguous "lanes" that must be counted to keep track of coarse position. Their phase is measured for fine positioning.
dr gemson, IIAEM, JU, Bangalore40The term 'dead-reckoning' abbreviated 'DR' stands for ‘Deduced Reckoning’ (i.e. calculation). This is the most common and widely used method of navigation.The DR navigation system must be reinitialized after any gap in radio coverage as errors accumulate and if electric power is lost.
dr gemson, IIAEM, JU, Bangalore41DEAD-RECKONING COMPUTATIONSOne nautical mile = 1852 metershRVMnorthhRVeastPLatitude = Longitude =
dr gemson, IIAEM, JU, Bangalore42
dr gemson, IIAEM, JU, Bangalore43References required on earth for efficient navigation – Geodesy, Map Projections and Coordinate SystemsMaps and Geodesy: WGS – 85 system; Coordinate system and transformation; Great circle and rhumb line navigation
dr gemson, IIAEM, JU, Bangalore44Geodesy – also known as geodetics, geodetic engineeringor geodetics engineering –
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- Summer '18