Noise Doppler-Shift Measurement of Airplane Speed

摘要

This paper illustrates a new and practical experimental technique for studying the Doppler effect1"^ where the pitch variation^ of noise from a passing aircraft is used to calculate its speed. The Doppler effect has many everyday applications that may already be familiar to students. One such application is Doppler echogra-phy, used mainly in medical imaging to measure the rate of blood flow through the heart and major arteries. Ultrasonic waves are bounced off of a target object. If the object is moving it changes the frequency of the echoes, and the amount of frequency change depends upon how fast the object is moving. In this way the speed of blood circulating through the imaged area can be measured.^ Another familiar application of the Doppler effect involves its use for measuring the speed of a vehicle, such as a car traveling on a highway. In this case microwaves are directed at a moving target, and the frequency change of the reflected waves is used to calculate the speed of the vehicle with respect to the radar source.