Calculator Inputs
Plotly Graph
The chart maps Doppler shift against corrected target velocity using your active settings.
Formula Used
Reflected echo
v = Δf × c / (2 × f₀ × cosθ)
Use this when the signal travels to a moving target and returns to the sensor. Common cases include radar speed measurement and pulse-echo ultrasound.
One-way received signal
v = Δf × c / (f₀ × cosθ)
Use this when the frequency shift is measured in a single travel path. This fits transmitter-to-receiver motion problems and simplified wave propagation setups.
How to Use This Calculator
- Choose reflected echo or one-way measurement mode.
- Enter the operating frequency and select its unit.
- Enter the measured Doppler shift and its unit.
- Select a preset medium or enter a custom propagation speed.
- Enter the beam angle relative to the target motion path.
- Pick the output unit and optional uncertainty percentage.
- Press Calculate Velocity to show results above the form.
- Review the chart, result table, and export buttons for reporting.
Example Data Table
| Scenario | Mode | Frequency | Shift | Medium | Angle | Estimated Velocity |
|---|---|---|---|---|---|---|
| Traffic radar | Reflected | 24 GHz | 1600 Hz | Light | 0° | 9.9931 m/s |
| Medical ultrasound flow | Reflected | 5 MHz | 3247 Hz | Soft tissue | 0° | 0.5000 m/s |
| Marine sonar target | Reflected | 200 kHz | 270 Hz | Water | 0° | 0.9990 m/s |
| Ultrasonic steel inspection | One-way | 2 MHz | 800 Hz | Steel | 15° | 2.4685 m/s |
Frequently Asked Questions
1. What does this calculator convert?
It converts a measured Doppler frequency shift into target velocity. You can apply reflected or one-way formulas, choose different wave speeds, and correct for beam angle.
2. When should I use reflected mode?
Use reflected mode when the wave leaves the sensor, bounces from the target, and returns. Radar guns and many ultrasound systems fit this case because the frequency shift happens over two travel legs.
3. Why does angle matter?
Doppler instruments read radial motion along the beam. If the target travels at an angle, the measured shift shrinks by the cosine of that angle. Correcting the angle estimates the true motion speed.
4. Which propagation speed should I choose?
Choose light for electromagnetic systems, water for sonar, soft tissue for medical ultrasound, air for acoustic tracking, and custom when your medium has a known measured speed.
5. What does a negative Doppler shift mean?
In this page, a negative shift is treated as receding motion. Some instruments define the opposite sign, so confirm your equipment convention before interpreting approach and retreat labels.
6. Is this calculator accurate at very high speeds?
It uses the classical Doppler model, which works well for most lab, traffic, sonar, and ultrasound cases. For speeds approaching a significant fraction of light speed, a relativistic model is better.
7. What do the CSV and PDF buttons export?
They export the visible result summary. CSV is useful for spreadsheets and batch records, while PDF is better for reports, printouts, and sharing measurement summaries with others.
8. Why include an uncertainty percentage?
Real measurements have noise, calibration limits, and angle error. The uncertainty input gives a quick velocity band, helping you communicate confidence instead of showing only one exact-looking number.