Drugs being dropped through prison cell windows, near misses with aircrafts, worries about injuries being caused or properties being damaged—drones have been getting quite a lot of bad press recently. As if these were not headaches enough, policy makers and insurers are scratching their heads over how to approach this novel, previously uncharted, terrain.

Drones, or Unmanned Aerial Vehicles (UAVs), have managed to create considerable excitement over the past few years—as well as no shortage of adverse media attention. Some of the negative issues are sketched out above. On the plus side, parcel delivery companies are hailing drones as the answer to delivering packages in difficult to reach areas, while emergency services and disaster relief agencies can use them to survey dangerous or damaged properties and areas that can’t be reached safely anymore following a catastrophic event (such as an earthquake). They can also be employed to pinpoint key areas for operatives to make more successful rescue attempts by using signals emitted by mobile phones or heat-seeking devices to show where there are indications of life beneath collapsed structures. Real estate professionals use drones to take aerial photographs of properties that are on their books, giving prospective purchasers views that they would not otherwise have access to.

All of this gives the drone makers considerable scope for development. At the same time, they’re also finding new realms to explore. While space, the final frontier, may be a tad too extreme a reach, the watery depths represent a more obvious (and easily accessible) challenge. But just as humans are not optimised for aquatic living, neither is it the best environment for drones.

Rescue required

The inhospitable nature of the sea makes an environment where rescue is all too often required, not only by conventional maritime users (sailors in both pleasure and commercial vessels), but by those in need of urgent disaster relief as well.

Figures put out by a UK think tank, the Overseas Development Institute (ODI), show that there are now twice as many disasters recorded on a global scale as there were 30 years ago. Many of them have a significant impact not only on land but also in the water. Ports can be damaged as a result of tsunamis, leaving underwater structures potentially in need of repair. Underwater drones have a vital role to play here, be it in mapping out areas of damage or sources of pollution.

Riding on the crest of popular technology

Much of the technology used by airborne drones is spun off from mass commercial avenues—mobile phone technology, for instance. The picture gets more clouded underwater. Even though 80% of the world’s inhabitants live close to water, the maritime environment is still relatively under-exploited in technological terms. There is no way that you can forget this is an alien environment. Optical technologies demonstrate limited applicability underwater, so too do most of the technologies on which airborne drones rely – namely cellular, wireless, GPS (satellite-based) and radar.

Things are not helped by the fact that, while the manufacturers of airborne drones have a wealth of bandwidth available to them for applying their technologies, the same cannot be said underwater. In any case, radio waves have limited transmission properties when submerged, particularly in a salty environment. Although penetration is better at lower frequencies, with one of the lowest frequencies available for public use, around 27MHz (which is often used for Citizens’ Band and ham radio), waves can travel just 3 metres.

And while both very and extremely low frequency (VLF and ELF) signals can be used over distances that can stretch up to tens of thousands of kilometres, to transmit their signals they need antennae that are themselves kilometres long. Underwater that presents more than a few practical issues. Couple that with the power needs of their transmitters and it’s straight back to the drawing board.

The promise of sonar

Sonar offers much better prospects for communication and navigation. Sound travels well in water, hence its use by aquatic mammals, such as whales and dolphins. Even so, there are still problems around high power consumption, low bandwidth and signal diffusion. The bandwidth that can be achieved with the current best underwater acoustic modems still falls short of the levels required to make real-time video feasible. Controlling an underwater robot from the surface of the sea is therefore akin to flying blind: Highly dangerous for all parties involved, and not the least for ocean inhabitants.

Even so, acoustic technology is useful for providing low resolution imaging. A drone-mounted array of small transducers can be used to determine the distance and angle of signals emitted from a beacon suspended upon the surface of the water.

It has been shown that high powered sonar, such as that used by the US Navy, can have a deleterious effect on mammals such as whales. It can cause them to breach and flee their normal feeding grounds. There have even been instances where the breach took place too rapidly, resulting in decompression sickness causing injury or death.

A lot of work on maritime drones remains to be done. Power and frequency issues, battery drain due to low temperatures, developing the artificial intelligence required to enable the drone to assume control when communication with the surface is interrupted—there are quite simply endless areas to develop and explore.

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