How Rain Impacts AIS Signal Transmission and Strategies to Combat Rain Interference

Rain acts like a virtual wall for radio waves. When heavy rain falls, the water droplets scatter AIS radio signals. Such scattering may lead to signal degradation or, in some cases, complete interruption.

You might be able to get away with a weaker signal if it’s only light rain, but heavier rain can cause considerable interference. The scattering effect is essentially due to the refraction and absorption of radio signals by the water droplets.

Radio waves, especially at higher frequencies like those employed by AIS, are weakened or diminished by rain. Therefore, there will be a decrease in range, and ships may not detect one another until they are dangerously close. When there are more ships in the area, the risk of collisions increases.

An efficient AIS transceiver with state-of-the-art filtering capability can help separate important signals from background noise. This means using systems with error correction to guarantee that, even if some parts of the signal are lost, enough pieces are received for successful reconstruction at the destination.

Change your route as necessary and try to go through regions where rain is expected to be light. There are times when shipping lanes have other ways to go that are meant to help avoid heavy weather. Don’t skip maintenance—make sure your AIS units are working well, with all antennas in good shape, to handle any adverse effects that weather may decide to bring.

 

The Fog Factor and Navigating

While radio frequencies are not greatly degraded by fog, confusion may arise. There may be an increase in signals arriving from different paths. This phenomenon, called multipath interference, happens when signals reflected off surfaces—like water or ship structures—reach the receiver slightly out of sync.

Given the conditions, such reflections are more probable, thus reducing the clarity of the AIS inputs. Signal attenuation occurs due to the increased atmospheric moisture, where signals lose strength by traveling through denser air and water vapor as opposed to dry conditions.

Fog reduces visibility. In this situation, reliance on electronic navigation aids is heightened. Misinterpretation of AIS data can cause delays in decision-making, which is undesirable when immediate actions are required during close-quarters situations. Ships relying heavily on AIS for collision warnings may find themselves at a disadvantage if signals become corrupted in fog.

It calls for a combination of human oversight and technological backup. Radar, by detecting the physical presence of nearby vessels or structures, offers a slight compensation for the loss of AIS signal and thus provides mariners with a real-time view of the surroundings.

Crew members are preparing for the inevitable- an encounter with navigation aids that will not be so clear (including radar). Practice, and let’s do it in a fog simulation environment. An additional validation measure that might really help is to maintain close communication with other ships via radio.

Another very wise step is to slow down—this will give the crew time to react in case they need to ask something about what they see on the AIS. Keep your eyes open – fog can hide more than signals—so keep looking and visually check what is happening.

 

Ways to Mitigate Thunderstorm Interference

Thunderstorms create electromagnetic disruptions that can mischief with radio frequencies. As a natural source of wideband radio frequency noise, lightning can interfere with AIS signals and cause inconsistencies or momentary loss of the system’s performance.

During such storms, the atmosphere gets charged with electricity. This can further noise VHF radios—the radios used by the AIS system. The problem escalates when ships venture onto the deck in the storm, surrounded by static and high-frequency noise that is intermingled with the very AIS signals, making it very difficult for the mariner to keep communication and navigation equipment free from problems.

Heavy rain is often accompanied by thunderstorms, which add complexity to the situation and further degrade existing rain-related difficulties to the quality of AIS signals. Immediate contingency measures are needed to protect maritime operations during such situations.

To protect AIS systems from the impact of thunderstorms, proper grounding and shielding techniques should be implemented. Advanced grounding technologies should be on ships to minimize significantly the possibility of electrical noise interference. Shielded AIS transceivers would help protect the electronics from induced electromagnetic pulses.

Another consideration is upgrading to equipment that performs well despite high-frequency noise. Many modern AIS transceivers come with built-in noise filters specifically designed for operation in heavy atmospheric disturbance. Regularly practicing emergency communication drills would help train ship personnel to shift to backup strategies if primary communication channels are degraded.

Employing predictive weather technologies, such as onboard weather tracking tools and apps, would allow for preemptive informing of anticipation and navigation strategy. Ships could avoid thunderstorm-prone areas completely, thereby reducing AIS signal interference and promoting operational safety by rerouting or rescheduling on-time arrivals.

 

Snow and Ice

Snowy waters—a canvas for a picture-perfect scene. But men and machines alike would face relentless challenges in such a situation, as anyone sailing there would tell you. In terms of interference, snow is not all that different from rain. AIS signal transmission is diminished under similar ripple effects just due to refraction and reflection.

If vessel equipment is covered in icy precipitation, the antennas might be less able to send and receive signals. A physical build-up of ice could completely block and cloak the antennas, thereby preventing systems like AIS from operating at peak efficiency. The ice itself could inflict physical damage to these vital antennas and degrade signal quality.

The presence of snow layer clouds, which are the same clouds that exist with snow, insulate signals that would have a direct line-of-sight path from source to receiver. Any degradation of the signal that travels directly would be exacerbated during extreme weather conditions, such as snow squalls.

Implementation of routine maintenance and de-icing measures onboard will enable AIS equipment to function properly, or at least to the fullest extent possible, during inclement weather. Disruption of signals may occur due to the accumulation of ice on antennas and other equipment, so this should be limited or eliminated by periodic inspections.

Just as backup antennas would, make sure extra ones are placed in safe locations to cover for one another when one set fails under the weight of ice.

Advance knowledge of snow bursts allows ships to prepare properly and change course if conditions appear uninviting. By plotting routes outside of known snow belts during periods of heavy snowfall, it is possible to minimize AIS navigation disruption.