Can a Sonic Boom Be Heard Underwater During a Supersonic Flight Above You?

The phenomenon of sonic booms during supersonic flights has always been a fascinating subject for both scientists and laypeople alike. Interestingly, the question arises: can a sonic boom be heard at ground level if you are underwater during an atmospheric supersonic flight above you? To answer this, we need to understand a few key aspects of sound propagation and the properties of different mediums.

Understanding Sonic Booms

A sonic boom occurs when an aircraft travels faster than the speed of sound (Mach 1). This creates a shock wave, which propagates outward in a cone shape. The pressure changes associated with this shock wave can be heard on the ground as a loud, startling noise, commonly compared to a thunderclap or a clap of hands.

Sound Propagation in Different Media

Sound travels at different speeds through different mediums. In dry air at room temperature (20°C or 68°F), sound travels at approximately 343 meters per second (m/s). However, in water, sound travels much faster, at about 1,482 meters per second (m/s). This is due to the higher density and molecular structure of water.

Given that sound travels faster in water, it's logical to suspect that underwater sounds might be amplified. Let's explore this in the context of a supersonic flight.

Can a Sonic Boom Reach Underwater?

Considering a supersonic aircraft flying above water at a high altitude, the sonic boom would first manifest in the air and propagate down to the water surface. Once the shock wave hits the water, it can cause a series of events:

Refraction: As the shock wave hits the water, some of the energy is refracted into the water. This can create subtle disturbances, but these are generally not enough to cause a audible sound underwater.

Reflection: More energy is usually reflected back into the air, as sound travels much more easily through air compared to water.

Compression and Expansion: In the air, the shock wave causes rapid compression and rarefaction of the air molecules. In water, similar pressure changes can occur but are typically much weaker and less sudden.

While these changes can create very minor disturbances in the water, they are generally not audible underwater. This is because the sonic boom, as experienced in air, is a rapid, sharp pressure change that is designed to be heard. Underwater, the nature of this pressure change is much gentler and more dispersed.

Real-world Observations and Experiments

There have been instances where underwater sounds have been recorded during supersonic flights. For example, during the testing of the Marine Stratospheric Sonolaser (MARSONIC), researchers noted certain low-frequency sounds that could be attributed to the shock wave as it interacted with the water. However, these were not typical sonic booms as experienced by observers on the ground. The sounds were more akin to underwater rumbles or vibrations, rather than a sharp, clear sonic boom.

Conclusion

In summary, while a sonic boom is a powerful and unmistakable event during atmospheric supersonic flight, the energy is largely directed into the air and not into the water. Thus, it is unlikely that one would be able to hear the traditional, sharp sound of a sonic boom underwater during a supersonic flight above you.

That being said, it is not impossible to notice some form of underwater disturbance during such events, but it would be more of a subtle change in water pressure or movement rather than a clear, audible sonic boom. This is a fascinating interplay of physics and engineering, highlighting the unique properties of different mediums and how they can (and cannot) transmit sound.

Additional Reading:
History of Supersonic Flight and the Overture Plane: The Future Is Supersonic
New Tel Aviv Study Hints There Actually Is a Silent Sonic Boom

Keywords: sonic boom, underwater hearing, atmospheric flight, supersonic sound