THE ACCURACY ANALYSIS OF THE MEASUREMENT OF AUTOMOBILE VELOCITY BY DOPPLER LASER METERS

Many instruments for velocity measurement are based on the physical phenomenon, a Doppler effect. The paper deals with accuracy of laser meters used in the measurement of automobile velocity. The measurement results of such devices as well as of any other electronic or mechanical devices inevitably possess errors. For error analysis we will use a probabilistic method assuming that only random errors are present. To analyse systematic errors algebraic methods are usually used expressing systematic error as a function of some variables. For that purpose special measurements are performed when the measurement results are compared with the known values of the variables or those having been measured by the devices of higher accuracy. The accuracy of measurement by Doppler meters depends mostly on the parameters of two kinds - stabilising and measuring laser emission frequencies and the errors of determining the emission speed in the atmosphere. These are the systematic errors of measurement. Other errors appear as a result of direct and indirect measurement of differential frequency. Since measurement is based on Doppler effect, the main parameter of emission affecting measurement accuracy is the frequency of emission. The influence of the changes in emission speed in the atmosphere due to the instability of atmospheric parameters on measurement accuracy is markedly weaker. A Doppler meter can operate in one system with a pulse- phase range-finder enabling the determination of the distance to a moving object. The measurement accuracy of such system is higher.