Calculator inputs
Formula used
Calculation steps
- Results and substitutions will appear after calculation.
All velocity conversions
| Unit | Converted value |
|---|---|
| No result available. | |
Calculation history
| Time | Mode | Velocity | Direction | Shift |
|---|---|---|---|---|
| No saved calculations. | ||||
How to use this calculator
- Select the physical application and frequency input method.
- Enter the transmitted frequency, observed frequency, or Doppler shift.
- Choose the propagation medium and any required geometry.
- Select the velocity unit, precision, and sign convention.
- Review the result, warnings, formula, and calculation steps.
Positive velocity represents approaching motion under the default convention. Negative velocity represents receding motion. Change the convention when your instrument reports opposite shift polarity.
Example data
| Application | Original frequency | Shift | Medium | Expected output |
|---|---|---|---|---|
| Police radar | 24.125 GHz | 2.5 kHz | Vacuum model | Radial road speed |
| Medical ultrasound | 5 MHz | 2 kHz | Soft tissue | Angle-corrected flow velocity |
| Sound source | 1 kHz | 30 Hz | Air | Source velocity |
| Astronomy | 500 THz | Frequency ratio | Vacuum | Relativistic radial velocity |
Frequently asked questions
What does a positive Doppler shift mean?
Under the default convention, positive shift means an approaching source or target. The received frequency becomes higher. Reverse the convention for instruments using opposite polarity.
Why does radar use a factor of two?
Monostatic radar measures a transmitted path and reflected return path. Both paths contribute Doppler shift. The velocity equation therefore includes two in its denominator.
When should I use the relativistic model?
Use it when velocity becomes a meaningful fraction of light speed. Classical estimates then become inaccurate. Astronomy commonly needs relativistic correction for larger spectral shifts.
What is radial velocity?
Radial velocity is motion along the measurement line. Sideways motion does not directly create radial Doppler shift. Angle correction estimates actual speed from measured radial speed.
Why is a ninety-degree ultrasound angle invalid?
The cosine of ninety degrees equals zero. Division by that factor is undefined. Near-right angles also amplify small measurement errors considerably.
What causes ultrasound aliasing?
Aliasing occurs when the measured shift exceeds the Nyquist limit. That limit is half the pulse repetition frequency. Increase PRF or adjust technique using qualified clinical guidance.
Can this calculator use wavelength?
Yes, select wavelength and frequency shift as the input method. The calculator converts wavelength into frequency. It uses the selected medium's propagation speed.
Does air pressure change sound speed here?
Pressure is recorded in the summary for reference. The simplified model uses temperature and humidity. Precision acoustic work may require a more detailed atmospheric model.
What does bistatic angle mean?
It is the angle between transmitter-target and target-receiver paths. The calculator assumes target motion along the angle bisector. Other geometries require vector analysis.
Can negative redshift values be entered?
Yes, values above minus one are accepted. Negative redshift indicates blueshift. The result is reported using the calculator's signed approach convention.
Are medical results suitable for diagnosis?
No, they are educational estimates only. Clinical ultrasound involves calibration, sampling, anatomy, and professional interpretation. Always rely on qualified medical equipment and personnel.