distant tropospheric distribution of radiowaves
an entrance signal
station air radio engineering investigations
accuracy of definition of range
It is usually considered to be, that in conditions of a normal atmospheric refraction range of radiohorizon is a constant determined in heights of the transmitter and the receiver. This circumstance causes an opportunity of the approached definition of range up to radar station (RS) with the help of station air radio engineering the investigations (REI), established on coming nearer to RS flying device (FD). For this purpose measurement of height of flight FD and the data on height of the aerial of a radar station above a spreading surface is necessary. Range up to RS is determined by registration by station of RTR of the moment of «occurrence» RS because of radiohorizon. Such definitions are expedient in cases when the lay of land is homogeneous, and the height of aerials of the transmitter is known precisely enough, in particular, with reference to ship RS. Methods in which for positioning FD concerning ship РЛС the phenomenon of «radiohorizon» is used, are applied in sea aircraft.
In article it is considered methods of an estimation of accuracy of definition of range by the equipment air РEI up to the working ship radar station, used at flights above the sea. It is supposed, that the flying device comes nearer to the ship, and the onboard equipment of REI measures levels of signals RS and a direction of their arrival. In first of considered methods on the basis of use of known parities for levels of a signal in area of «a superficial shadow» and «light» the distance which flies by flying device in direction RS during which the level of capacity of an entrance signal intensively (in steps) increases is estimated, exceeding on size some threshold level. The order of errors of definition of range and a condition of realization of this definition is estimated.
In the second method considered in article, experimental dependences of reduction of a level of a signal in area of «penumbra» and «shadow» are used in process of removal from the radiohorizon, published in the collective monography under B.A.Vvedenskogo's edition. Ratio for continuous function of a level of an entrance signal from range are resulted at transition from area of «penumbra» in area of «light». Thus the factor of reflection from a sea surface and a multiplier of an interference is taken into account. For carrying out of calculations on analytical imitating model at different lengths of waves and different polarization the approached approximations of experimental schedules are received. In result dependences of sizes of the first and second derivative of an entrance signal are found in the field of settlement range of radiohorizon. For the account of the casual errors causing deviations from the linear law of increase of a level of a signal in process of approach FD to RS from area of «shadow» in area of «light», mistakes are imposed. These mistakes are considered independent of measurement to measurement and are distributed under the normal law concerning average, equal to true value and with a dispersion proportional to a square of average. The border of necessity of application of averagings on one of algorithms is approximately illustrated.
The considered methods testify to an opportunity of reception of accuracy of definition of range up to RS a method of the «radiohorizon», a measured relative error from units (at small errors of measurement of levels of a signal concerning the dependence incorporated in the program) up to first two tens percent (at rather big errors). Accuracy in the determining image depends on characteristics of troposphere at the moment of supervision, volume of an available databank and a correctness of the account of these characteristics algorithms of data processing of measurements. Thus the greatest influence on accuracy render «fast», not predicted changes, as against «slow» supervision not shown during one session.