Doppler is a name (Christian Doppler) and should be capitalized.

Is Doppler supposed to be capitalized?

capitalized because it refers to Christian Johann Doppler, an Austrian physicist (1803–1853). He described a phenomenon whereby the frequency of sound changes when it is reflected off a moving object. ... If frequency (rather than amplitude) is analysed, one can detect motion on the basis of Doppler shifts.

What does Doppler mean?

1 : of, relating to, or utilizing a shift in frequency in accordance with the Doppler effect. 2 : of, relating to, using, or produced by Doppler ultrasound a Doppler examination Doppler images.