doppler shift
DOPPLER SHIFT
Doppler is the apparent change in wavelength (or frequency) of an electromagnetic or acoustic wave when there is relative movement between the transmitter (or frequency source) and the receiver.
Summary RF Equation for the Two-Way (radar) case
2(VXmtr % VTgt) fXmt f Rec ' fXmt % fD ' fXmt % c Summary RF Equation for the One-Way (ESM) case
V
f f Rec ' fXmt % fD ' fXmt % Xmtr or Rec Xmt c Rules of Thumb for two-way signal travel
(divide in half for one-way ESM signal measurements)
At 10 GHz, fD –
35 Hz per Knot
19 Hz per km/Hr
67 Hz per m/sec
61 Hz per yd/sec
20 Hz per ft/sec
To estimate fD at other frequencies, multiply these by: fXmt (GHz)
10
The Doppler effect is shown in Figure 1. In everyday life this effect is commonly noticeable when a whistling train or police siren passes you. Audio Doppler is depicted, however Doppler can also affect the frequency of a radar carrier wave, the PRF of a pulse radar signal, or even light waves causing a shift of color to the observer.
Waves
Stretched
Waves
Compressed
Frequency
Increase
ZOOM !! Frequency
Decrease
Figure 1. Doppler Frequency Creation From Aircraft Engine Noise
How do we know the universe is expanding?
Answer: The color of light from distant stars is shifted to red (see Section 7-1: higher 8 or lower frequency means Doppler shift is stretched, i.e. expanding).
A memory aid might be that the lights from a car (going away) at night are red (tail lights)!
2-6.1
Doppler frequency shift is directly proportional to velocity and a radar system can therefore be calibrated to measure velocity instead of (or along with) range. This is done by measuring the shift in frequency of a wave caused by an object in motion (Figure 2).
* Transmitter in motion
* Reflector in motion
* Receiver in motion
* All three
For a closing relative velocity:
* Wave is compressed
* Frequency is increased
For an opening relative velocity:
* Wave is stretched
*
Doppler is the apparent change in wavelength (or frequency) of an electromagnetic or acoustic wave when there is relative movement between the transmitter (or frequency source) and the receiver.
Summary RF Equation for the Two-Way (radar) case
2(VXmtr % VTgt) fXmt f Rec ' fXmt % fD ' fXmt % c Summary RF Equation for the One-Way (ESM) case
V
f f Rec ' fXmt % fD ' fXmt % Xmtr or Rec Xmt c Rules of Thumb for two-way signal travel
(divide in half for one-way ESM signal measurements)
At 10 GHz, fD –
35 Hz per Knot
19 Hz per km/Hr
67 Hz per m/sec
61 Hz per yd/sec
20 Hz per ft/sec
To estimate fD at other frequencies, multiply these by: fXmt (GHz)
10
The Doppler effect is shown in Figure 1. In everyday life this effect is commonly noticeable when a whistling train or police siren passes you. Audio Doppler is depicted, however Doppler can also affect the frequency of a radar carrier wave, the PRF of a pulse radar signal, or even light waves causing a shift of color to the observer.
Waves
Stretched
Waves
Compressed
Frequency
Increase
ZOOM !! Frequency
Decrease
Figure 1. Doppler Frequency Creation From Aircraft Engine Noise
How do we know the universe is expanding?
Answer: The color of light from distant stars is shifted to red (see Section 7-1: higher 8 or lower frequency means Doppler shift is stretched, i.e. expanding).
A memory aid might be that the lights from a car (going away) at night are red (tail lights)!
2-6.1
Doppler frequency shift is directly proportional to velocity and a radar system can therefore be calibrated to measure velocity instead of (or along with) range. This is done by measuring the shift in frequency of a wave caused by an object in motion (Figure 2).
* Transmitter in motion
* Reflector in motion
* Receiver in motion
* All three
For a closing relative velocity:
* Wave is compressed
* Frequency is increased
For an opening relative velocity:
* Wave is stretched
*