Can someone give me a tutorial on how doppler chronographs work? I understand the basics, but how does it determine how far a bullets travels in a given time length (sky screens are easy to understand as they are X ft apart). Does it just collect the one data point (i.e. it detects a projectile and “starts”, then detects it again and “stops”) or does it collect numerous data points over numerous distances and then through a mathematical program determine initial velocity?
I watched a video on the new Garmin on their website. As the bullet passes through the radar the returns hit the machine and it uses a math formula to calculate the speed.
What is cool is that they calculate that speed every couple of feet over several hundred yards, not just muzzle velocity. That is how companies like Hornady are saying they have verified BC's.
A true sportsman counts his achievements in proportion to the effort involved and fairness of the sport. - S. Pope
Everything I have read about the doppler systems seems to say that it is very accurate and you don't have to rely on lighting or shooting through skyscreens.
The principle of the Doppler effect is that a transmitter sends an oscillatory waveform (sound wave, radio wave, optical wave, etc. Doppler radar uses radio waves, lidar uses light waves) at a given frequency, and when this waveform hits something and reflects back to the transmitter, the frequency of the wave changes if the object it hit was moving. If the object is moving toward the transmitter, the frequency increases (called a "blue shift"). If the object is moving away from the transmitter, as is the bullet in this case, the reflected frequency decreases (called a "red shift"). The amount of change in the frequency corresponds to the velocity of the moving object. You can look up "Doppler shift" or "Doppler effect" to read more about it.
A single data point can be used to calculate the speed of the bullet. Multiple data points can be used to calculate the rate of change in the bullet's speed, which allows the calculation of the drag model and ballistic coefficient.
Last edited by Jordan Smith; 12/19/23. Reason: Hasty mistake
Only one minor note: Red shift is moving away from the transmitter (distance increasing). Blue shift is moving towards the transmitter (distance decreasing).
Only one minor note: Red shift is moving away from the transmitter (distance increasing). Blue shift is moving towards the transmitter (distance decreasing).
The principle of the Doppler effect is that a transmitter sends an oscillatory waveform (sound wave, radio wave, optical wave, etc. Doppler radar uses radio waves, lidar uses light waves) at a given frequency, and when this waveform hits something and reflects back to the transmitter, the frequency of the wave changes if the object it hit was moving. If the object is moving toward the transmitter, the frequency increases (called a "blue shift"). If the object is moving away from the transmitter, as is the bullet in this case, the reflected frequency decreases (called a "red shift"). The amount of change in the frequency corresponds to the velocity of the moving object. You can look up "Doppler shift" or "Doppler effect" to read more about it.
A single data point can be used to calculate the speed of the bullet. Multiple data points can be used to calculate the rate of change in the bullet's speed, which allows the calculation of the drag model and ballistic coefficient.
We all have life experience with Doppler effect but with sound, not EM energy.
The noise of a train or car coming at a person gets higher and higher pitched at it approaches and then gets lower and lower as it passes.
NASCAR races are a great example.
John Burns
I have all the sources. They can't stop the signal.
What is cool is that they calculate that speed every couple of feet over several hundred yards, not just muzzle velocity. That is how companies like Hornady are saying they have verified BC's.
Does anyone know how far downrange the new Garmin Xero measures speeds?
