Frequency change with velocity change

[JeremyA]

Does the received frequency at a location differ from the transmitted frequency when the medium velocity differs at the two locations?

To give a concrete example, a sub-sea pinger is transmitting at 37.5 Khz 4,000 metres below sea level and at a particular pressure, salinity, and temperature. A receiver nearer the surface detects the signal at a different pressure, temperature, and salinity. Finally a surface vessel detects the signal under yet another set of pressure, temperature and salinity.

For reference the velocity of sound in the oceans can vary by up to 10% due to these factors.

My intuitive guess is that sound transmitted in a high velocity domain will increase in frequency when it hits a low velocity domain?

 

[UltrafastPED]

No ... frequency does not change with the media; only the wavelength changes.

Speed = frequency x wavelength; so if the speed changes (due to the media), then the wavelength must change.

Frequency is the driver ...

 

[paisiello2]

Suppose for simplicity there existed a distinct boundary between the two mediums. And further suppose that we watched the crest of the wave from the time it hit the boundary and traveled onward in the lower velocity medium. This crest will not have traveled a full wave length by the time the following crest hits the boundary. This has the effect of shortening the wave length. But since the speed also is shortened then the frequency remains constant.

 

[Entanglement]

The Frequency of the wave ONLY depends on the source producing it, If the source makes 30 thousand complete oscillations in one second then all the particles affected by the waves will make 30 thousand complete oscillations and the frequency will be 30 kHz,
the velocity of propagation of the wave ONLY depends on the medium while the wave length depends on both the frequency and the velocity of the wave according to this equation velocity = frequency x wave length

 

[PJC01]

I can confirm that the received frequency at a location will differ from the transmitted frequency when the medium velocity differs at the two locations. This is due to the Doppler effect, which is the apparent change in frequency of a wave when the source and the observer are in relative motion. In this case, the medium velocity is the source of the wave, and the receiver and surface vessel are the observers.

According to the Doppler effect, if the medium velocity is higher at the source than at the receiver, the received frequency will be higher than the transmitted frequency. This is known as a blue shift. Similarly, if the medium velocity is lower at the source, the received frequency will be lower than the transmitted frequency, known as a red shift.

In the example provided, as the sub-sea pinger transmits at 37.5 kHz at a particular set of conditions, the receiver nearer the surface will detect the signal at a different frequency due to the change in medium velocity. And the surface vessel, detecting the signal under yet another set of conditions, will also receive a different frequency due to the change in medium velocity.

Furthermore, the change in frequency due to the Doppler effect can be calculated using the formula: observed frequency = emitted frequency x (velocity of sound at receiver / velocity of sound at source). So, in this case, the observed frequency at the receiver will be higher or lower depending on the difference in medium velocity compared to the source.

In conclusion, the received frequency at a location will differ from the transmitted frequency when the medium velocity differs, and this can be explained by the Doppler effect. It is important to consider the varying factors that can affect the velocity of sound in order to accurately interpret and analyze data collected from different locations.