74
4 Measuring Principles and Techniques …
f i = f 0 i
1 −
2V r
c
,
(4.26)
where f 0 i —frequency of i-component of spectrum of radar radiating signal; f i —
frequency i-component of receiving reflected signal. Hence, a spectrum width of the
whole receiving signal also changes, compared to a radiated one. Where at oncoming
movement of a target and radar platform the spectrum expands, and at distant movement—narrows. However, in practice, when V r c, these changes usually are
small. For this reason, the main influence effect on spectrum of velocity relatively to
radar and target displacement is a shift of the whole spectrum in F d value for carrier
frequency of a signal. The spectrum width is left almost unchangeable.
In radar navigational systems, a signal with f 0 frequency is radiated by the system,
located on moving object, which performs receiving functions as well. A signal
f rcv comes to input of measuring system. Let us examine different situations, when
Doppler receive–transmit system, mounted on object, moving with V velocity.
1. No wind, beam of the system is directed to ground surface at γ 1 angle, positioned
in vertical plane passing through an object axis. Then:
F d1 =
2V cosγ 1
c
f 0 .
(4.27)
2. No wind, beam of the system is directed to ground surface at γ 1 angle, positioned
in vertical plane which is deviated at γ 2 angle relatively to vertical plane passing
through an object axis. In this case:
F d2 =
2V cosγ 1 cosγ 2
c
f 0 ,
(4.28)
3. Horizontal wind U is presented, object velocity with reference to wind V 1 , object
drift angle α d . Beam of the system is directed to ground surface at γ 1 angle,
positioned in vertical plane which is deviated at γ 2 angle relatively to vertical
plane passing through an object axis. In this case:
F d2 =
2V 1 cosγ 1 cos(γ 2 + α d )
c
f 0 .
(4.29)
In third situation, there is a possibility to measure an object moving velocity and
drift angle, stipulated by the wind. However, by one measuring, this is practically
impossible to do, since it is impossible uniquely determine an object velocity and
drift angle. This ambiguity is increased when an object moving not only in horizontal
plane. To eliminate an ambiguity in onboard velocity and drift angle measuring
Doppler systems, measurements by three or four beams are conducted.
Correlation velocity measurement method. Let us examine an object, moving
in parallel to ground surface with V velocity. Three antennas: radiating antenna A r
4 Measuring Principles and Techniques …
f i = f 0 i
1 −
2V r
c
,
(4.26)
where f 0 i —frequency of i-component of spectrum of radar radiating signal; f i —
frequency i-component of receiving reflected signal. Hence, a spectrum width of the
whole receiving signal also changes, compared to a radiated one. Where at oncoming
movement of a target and radar platform the spectrum expands, and at distant movement—narrows. However, in practice, when V r c, these changes usually are
small. For this reason, the main influence effect on spectrum of velocity relatively to
radar and target displacement is a shift of the whole spectrum in F d value for carrier
frequency of a signal. The spectrum width is left almost unchangeable.
In radar navigational systems, a signal with f 0 frequency is radiated by the system,
located on moving object, which performs receiving functions as well. A signal
f rcv comes to input of measuring system. Let us examine different situations, when
Doppler receive–transmit system, mounted on object, moving with V velocity.
1. No wind, beam of the system is directed to ground surface at γ 1 angle, positioned
in vertical plane passing through an object axis. Then:
F d1 =
2V cosγ 1
c
f 0 .
(4.27)
2. No wind, beam of the system is directed to ground surface at γ 1 angle, positioned
in vertical plane which is deviated at γ 2 angle relatively to vertical plane passing
through an object axis. In this case:
F d2 =
2V cosγ 1 cosγ 2
c
f 0 ,
(4.28)
3. Horizontal wind U is presented, object velocity with reference to wind V 1 , object
drift angle α d . Beam of the system is directed to ground surface at γ 1 angle,
positioned in vertical plane which is deviated at γ 2 angle relatively to vertical
plane passing through an object axis. In this case:
F d2 =
2V 1 cosγ 1 cos(γ 2 + α d )
c
f 0 .
(4.29)
In third situation, there is a possibility to measure an object moving velocity and
drift angle, stipulated by the wind. However, by one measuring, this is practically
impossible to do, since it is impossible uniquely determine an object velocity and
drift angle. This ambiguity is increased when an object moving not only in horizontal
plane. To eliminate an ambiguity in onboard velocity and drift angle measuring
Doppler systems, measurements by three or four beams are conducted.
Correlation velocity measurement method. Let us examine an object, moving
in parallel to ground surface with V velocity. Three antennas: radiating antenna A r