Longitudinal wave and seismic P-waves (created by earthquakes and explosions). In longitudinal waves, the displacement of the medium is parallel to the propagation of the wave, and waves can be either straight or round. A wave along the length of a stretched Slinky toy, where the distance between coils increases and decreases, is a good visualization. In the case of longitudinal harmonic sound waves, the frequency and wavelength can be described by the formula where: The quantity "x"/"c" is the time that the wave takes to travel the distance "x". The ordinary frequency ("f") of the wave is given by The wavelength
Continuous-wave radar with the fact that it is coherent means that Fourier integration can be used rather than azimuth integration providing superior signal to noise and a Doppler measurement. Doppler processing allows signal integration between successive receiver samples. This means that the number of samples can be increased to extend the detection range without increasing transmit power. That technique can be used to produce inexpensive stealthy low-power radar. CW performance is similar to Pulse-Doppler radar performance for this reason. Unmodulated continuous wave radar cannot measure distance. Signal amplitude provides the only way to determine which object corresponds with which speed measurement when