FAQ - Frequently Asked Questions
Q: What is ShippingNoise.com ?
A: This site shows modelled level of underwater noise generated by large shipping traffic - the so called shipping noise. Shipping is one of many ways to introduce man made noise into the marine environment.
Q: Why did you create this site ?
A: Our objective is to show the contribution of shipping to the antropogenic (man made) underwater noise level, which is a chronic form of polluting our oceans today. Underwater noise has been the topic of various studies with respect to the effects on marine life. This site does by no way show actual in-situ measurements. Data is obtained from an underwater acoustic model, however due to the notorious dificulty in performing actual measurements it can be used as an aproximation.
Q: What is underwater noise?
A: Underwater noise is the result of the introduction of energy in the form of mechanical waves into an underwater media. In this case we mean the marine environment.
Q: What is the SPL at which marine life is affected ?
A: There is no direct answer to this as this has been and continues to be a topic of scientific research. Generaly speaking, ceteaceans and other marine fauna have different hearing patterns which are sensitive to certain frequencies and pressure levels. We may in the future include some marine life hearing thresholds obtained from public scientific studies.
Q: How do you obtain the sound level visible in the figure?
A: The figure shows a surface of rms Sound Pressure Level (SPL) of underwater noise generated by the passing ship traffic. To generate this surface, it requires the position of ships, the radiated noise level, and environmental data such as bathymetry, sound velocity and seafloor parameters. These data serve as input for an acoustic propagation model that generates the SPL surface. This process is repeated every 10 minutes with new vessel positions, as to generate a time series of instant noise maps. These SPL surfaces are processed for obtaining statistical indicators that allow to extract meaningful information. The statistical indicators shown here are level exceeded 95% of the time (p05), level exceeded 5% of the time (p95), and average SPL.
Q: How do you obtain ship positions?
A: The ship positions are obtained by means of AIS data. This AIS data is made available through the AIS data sharing site www.aishub.net
Q: What is AIS?
A: AIS stands for Automatic Identification System. Large ships are equipped with an AIS transmitter, to avoid colisions at sea. The transmission consists of a message containing several parameters, such as User ID, position, speed, heading, ship type, and several other relevant parameters. Check the AIS wikipedia entry
for more information.
Q: Which ships are shown? Why do they seem to disappear sometimes?
A: Most ships are container ships, oil tankers, cruise ships that may cruise at positions distant from AIS receivers located on land, and therefore the reception of AIS radio signals from a
given ship is not guaranteed at all time.
Q: Why do you only show areas in Portugal, Spain, and The Channel?
A: Currently there is AIS data with acceptable quality available for these areas. The main constraint is the processing capacity needed to calculate the underwater noise maps. The larger the area the longer it takes to compute. We will update the areas as this project progresses.