What are Hydrophones?
A hydrophone is an underwater device that detects and records ocean sounds from all directions.
People often think that the underwater world is silent. But this cannot be further from the truth. In fact, sound travels farther and faster in our oceans. From aquatic life, ambient noises and even planetary events like volcanoes or earthquakes, they can all make the oceans quite loud.
Just as a microphone collects sound in the air, a hydrophone detects acoustic signals under the water. Most hydrophones use ceramics that produce a small electrical current when subjected to changes in underwater pressure. When sound, which is a wave, arrives at these hydrophones that creates varying electrical currents. These varying signal strengths over time are a useful tool to better understand our marine environments.
Environmental Influences and Sensitivity
Sound in water is affected by the temperature, salinity and acidity of the water.
The changing density of water greatly impacts how sound travels. This means that temperature, salinity and acidity of water all change the characteristics of the aquatic environment. A perfect storm of conditions can create acoustic dead zones in the ocean, where no sound gets in or out. Submarines have been known to use these to hide from detection.
The depth zone where temperature rapidly changes is referred to as the Thermocline. Similarly, the area of rapid salinity change is the Halocline. These zones are susceptible to acoustic communication disruptions.
Reducing salinity can lead to loss of acoustic signal strength. This happens because the density of particles in water reduces. But the opposite is true when temperature decreases, causing acoustic signals to get amplified due to higher densities. Areas of oceans where both these change rapidly can create acoustic dead zones; an anomaly where no external sound gets in, and internal sounds remain trapped inside.
Rising acidity also increases loudness of sounds in the ocean. This can be good for artificially transmitted signals, but since it also increases background noise, it means that marine life suffers as climate change is increasingly acidifying our oceans too.
