In this Innovation Lab post, you will learn how to implement speed measurement using the A121 Pulsed Coherent Radar sensor. For example, the speed of cars and time gaps between each car can be tracked to monitor traffic but also the speed of small objects such as golf, tennis or soccer balls.
More information about the algorithm can be found on the Acconeer document site.
In the Exploration Tool, click “Speed detector” on the left-side menu, then adjust the distance to the approximate distance that you wish to measure speed at. This might require some adjustment to get an optimal measurement. If the range includes multiple distances, you will get a speed for each distance measured.
To start measuring, click “Start measurement” on the right-side menu. The speed is shown at “Speed history” on the Exploration tool, and the sign of the value tells whether the object is moving towards or away from the sensor (negative values means movement towards the sensor, and positive means away from the sensor). Note that only the movement component perpendicular to the sensor is measured, so when measuring at an angle, this needs to be taken into consideration.
On the Frequency data section, the power spectral density (PSD) of the signal is shown. The PSD of the signal describes the power present in the signal as a function of frequency. If the amplitude of the PSD goes above a threshold, it will be interpreted as a speed and displayed in the output. The threshold value is relative the the median of the PSD. So a threshold of 10 means that we need an amplitude of 10 times the median of the entire PSD to consider a speed. Lowering the threshold will mean that less reflective objects will start to affect the measurement as well.