Automatic Identification System (AIS)

Automatic Identification System, more popularly known as AIS is a system which helps to pinpoint the location and other navigational statistics of ships. AIS uses VHF radio channels as transmitters and receivers to send and receive messages between ships which endeavors to fulfill a lot of responsibilities.

AIS behaves as a radar and enables ships to correspond with other ships and in the case of coast guards, aids them in tracking any untoward sightings in the ocean. Additionally, it also helps in navigational purposes like transmitting alternative routes in case there are chances of any on-course collision between two ships. AIS also enables in sending distress signals so that rescue operations can be carried out for the affected ship. Also, in cases where accidents have occurred and evidence needs to be found out about the last known position and route of the ship, it is the AIS that assists the authorities to find the required details. Just like the Black Box in an airplane, the AIS has managed to revolutionize and streamline marine travel, navigation and communication aspects.

In today’s times, AIS solves many problems pertaining to the transmission of communication across the naval communication lines. By using normal communication channels VHF radios, AIS solves the problem to integrating contemporary technology with the already existing ones. Also since the transmitting and receiving codes are automatic, it becomes quite evident as to which ship is transmitting or receiving signals thereby making matters of keeping track of the ship simple and uncomplicated.

Since marine rules stipulate that every ship needs to have an AIS fitted in its marine equipment catalogue, it becomes easier and feasible for pinpointing the locations and routes taken by ships in the high seas and oceans. This part becomes more relevant considering the incidents and events that have occurred and are occurring in these past few years, because of the threat of pirates and marine terrorism increasing more and more every day. Therefore with the usage of a device like AIS such complications can be avoided as coast guards can help shipmen navigate away from those water parts where the threat of piracy looms.

Right now, it also has to be understood that AIS is burdened by distance problems, in the sense that AIS is only applicable for area of 74 km. But as more and more ships find the system to be useful and highly facilitative in their navigational routes, the time is not far when AIS will encompass a wider area than what it covers now. Already, it boasts of facilities like providing satellite connectivity and internet plugging to enable a much better scope for the gadget’s assistance.

By making use of a gadget like the AIS, charting the routes and locations of ships has become very simple. Marine travel is one of the oldest forms of transportation and with the inclusion of such a gadget in routine marine travel, the older means of transport has become quite contemporary as it has become possible for ships and coast guards to be aware of the happenings in the waters immediately surrounding them. AIS is the answer to all communication problems that were being caused while a ship was in the water and being an appropriate answer suiting all intents and purposes, the AIS technology is something that will evolve and develop as years progress by, making matters even more convenient for the marine vessels and travelers in the days to come.

Global Positioning System (GPS)

The Global Positioning System (GPS) has changed the way the world operates. This is especially true for marine operations, including search and rescue. GPS provides the fastest and most accurate method for mariners to navigate, measure speed, and determine location. This enables increased levels of safety and efficiency for mariners worldwide.

It is important in marine navigation for the ship's officer to know the vessel's position while in open sea and also in congested harbors and waterways. While at sea, accurate position, speed, and heading are needed to ensure the vessel reaches its destination in the safest, most economical and timely fashion that conditions will permit. The need for accurate position information becomes even more critical as the vessel departs from or arrives in port. Vessel traffic and other waterway hazards make maneuvering more difficult, and the risk of accidents becomes greater.

Mariners and oceanographers are increasingly using GPS data for underwater surveying, buoy placement, and navigational hazard location and mapping. Commercial fishing fleets use GPS to navigate to optimum fishing locations, track fish migrations, and ensure compliance with regulations.

An enhancement to the basic GPS signal known as Differential GPS (DGPS) provides much higher precision and increased safety in its coverage areas for maritime operations. Many nations use DGPS for operations such as buoy positioning, sweeping, and dredging. This enhancement improves harbor navigation.

Governments and industrial organizations around the world are working together to develop performance standards for Electronic Chart Display and Information Systems, which use GPS and/or DGPS for positioning information. These systems are revolutionizing marine navigation and are leading to the replacement of paper nautical charts. With DGPS, position and radar information can be integrated and displayed on an electronic chart, forming the basis of the Integrated Bridge System which is being installed on commercial vessels of all types.

GPS is playing an increasingly important role in the management of maritime port facilities. GPS technology, coupled with geographic information system (GIS) software, is key to the efficient management and operation of automated container placement in the world's largest port facilities. GPS facilitates the automation of the pick-up, transfer, and placement process of containers by tracking them from port entry to exit. With millions of container shipments being placed in port terminals annually, GPS has greatly reduced the number of lost or misdirected containers and lowered associated operation costs.

GPS information is embedded within a system known as the Automatic Identification System (AIS) transmission. The AIS, which is endorsed by the International Maritime Organization, is used for vessel traffic control around busy seaways. This service is not only vital for navigation, but is increasingly used to bolster the security of ports and waterways by providing governments with greater situational awareness of commercial vessels and their cargo.

AIS uses a transponder system that operates in the VHF maritime band and is capable of communicating ship to ship as well as ship to shore, transmitting information relating to ship identification, geographic location, vessel type, and cargo information -- all on a real-time, wholly automated basis. Because the ship's GPS position is embedded in these transmissions, all essential information about vessel movements and contents can be uploaded automatically to electronic charts. The safety and security of vessels using this system is significantly enhanced.

Finally, with the modernization of GPS, mariners can look forward to even better service. In addition to the current GPS civilian service, the United States is committed to implementing two additional civilian signals. Access to the new signals will mean increased accuracy, more availability, and better integrity for all users.

Differential Global Positioning System (DGPS)

                                           What is DGPS?

Differential Global Positioning System (DGPS) is a method of providing differential corrections to a Global Positioning System (GPS) receiver in order to improve the accuracy of the navigation solution. DGPS corrections originate from a reference station at a known location. The receivers in these reference stations can estimate errors in the GPS because, unlike the general population of GPS receivers, they have an accurate knowledge of their position. As a result of applying DGPS corrections, the horizontal accuracy of the system can be improved from 100m (95% of the time) to better than 10m (95% of the time).

More importantly, the reference stations provide integrity monitoring, warning users to disregard a satellite which is operating outside of specification. With DGPS, this warning happens within a few seconds of the satellite becoming 'unhealthy', compared to GPS warnings where some hours can elapse.

The most common form of DGPS used internationally for maritime navigation operates in the MF Radiobeacon band (285-325 kHz) and conforms to the RTCM Recommended Standards for Differential Navstar GPS Service for the transmission of data. This form of DGPS uses pseudorange corrections and range-rate corrections from a single reference station which has sufficient channels (typically 12) to track all satellites in view. Pseudoranges (distance measurements) are simultaneously measured to all satellites in view, and using the known (surveyed) position of the receiver's antenna and the positional (ephemeris) data from each satellite, the errors in the pseudoranges are calculated. These errors are converted to corrections and are broadcast to user receivers.

The users GPS receiver applies the corrections to the pseudoranges measured to each satellite used in its position calculation. The GPS receiver always applies the latest (ie. newest) corrections received.

Using this method, and depending on the user-to-reference station separation and the age of the corrections being applied, accuracies better than 10 metres (95%) are achievable.

As the user-to-reference station separation increases, the signal from the satellite to the user takes a different path through the atmosphere compared to the signal from the satellite to the reference station. Due to variations in the atmosphere, there is a different signal delay at the user receiver compared with the delay at the reference station.

The greater the user-to-reference station separation, the less the satellite ephemeris errors are corrected. This is because different line-of-sight vectors to the satellite from the reference station and from the user produce different perceived ephemeris errors.

As a result of the range decorrelation of the atmospheric and ephemeris errors, the further the user is from the reference station, the less accurate the navigational accuracy can be.

E-Loran

LORAN, short for long range navigation, was a hyperbolic radio navigation system developed in the United States during World War II. It was similar to the UK's Gee system but operated at lower frequencies in order to provide improved range up to 1,500 miles (2,400 km) with accuracy of tens of miles. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft, but found its main use on the ships and aircraft operating in the Pacific theatre. LORAN, in its original form, was an expensive system to implement, requiring a cathode ray tube (CRT) display. This limited use to the military and large commercial users. Use was never widespread, and by the time new receivers were available in the 1950s, the same improved electronics led to new systems with higher accuracy. 

eLoran is a low frequency terrestrial navigation system based on a number of transmission stations, which emit precisely timed and shaped radio pulses centred at 100 kHz radio frequency. Each station emits a sequence of 8 pulses spaced 1000 microseconds apart. The stations are grouped into chains, which each consists of a single master station and two or more secondary stations. The master station transmits first, followed by successive transmissions from each of the secondary stations of the chain. The master/secondary transmission sequence is repeated periodically, with the period between repetitions called the Group Repetition Interval (GRI).

eLoran represents a move away from the hyperbolic Loran-C of old. Today, modern receivers can measure the "time of arrival" of signals from many stations (and from multiple chains) at once. eLoran is derived from the Loran-C system, but uses solid-state transmitters, precise timing (using atomic clocks) and a data channel to provide correction and integrity messages. The use of built-in microprocessors means that the receiver is also able to output latitude and longitude directly. Modern eLoran works in much the same way as GPS but it is an independent and complementary system, offering a navigation system with no failure modes in common with GPS or any other satellite based system.

eLoran, together with a future maritime service of differential-Loran covering approaches to major UK and Irish ports, can offer the increased accuracy, integrity, and continuity of service modern navigators demand.

Handhelds for Marine Technology

Handheld receivers are usually just as accurate as any other type, so accuracy shouldn't be an issue when deciding which type to choose. The low cost of a handheld is the chief advantage, as some are available for less than $100 US. Another plus is the ability to use it hiking or in the car. Keep in mind that you, your boat, and your handheld will all be moving, so the small buttons will be difficult to use at times. Most units accept an optional mounting bracket and this would free up an extra, valuable hand. The location of the GPS needs to be considered, as you need to be able to see the screen easily. Will it be in direct sunlight? If so, choose a model with a screen that can be read in that situation. Screen size can vary a lot from model to model, so consider that you will want to be able to see the screen without discomfort. Location again comes into play regarding the antenna. GPS does not work well when held close to the body or through metal. Test the area you are thinking about placing the receiver by looking at the signal strength of the satellites. If the signal is not good where you need to put it, an external antenna is an option for some models. Since a GPS receiver runs on batteries, an external power source would be a good idea. Just make sure the model you get can run off of external power. Garmin makes a line of handheld models for marine use.

Marine GPS: Take to the Open Waters

Marine GPS navigation requires knowledge above and beyond land navigation. Rocks, shallow water, and wrecks are common obstacles, and since fog often occurs on coastal waters, it's critical to know where you are. Recreational boaters usually stick close to land and this may seem to be a clear advantage, but that is where the majority of hazards are. GPS gives your location, but you need additional information: charts.

Chartplotters are a big improvement over handhelds. They display the GPS information overlaid on the nautical charts. While not a complete replacement for paper charts, the chartplotter will be the primary navigation tool. The screens are larger, there are usually more buttons, and the buttons are larger. They are meant to be mounted to a fixed surface, and they usually have external antennas, so placement is not an issue. Chartplotters start at about $400 US and screen sizes vary from about 5 - 10 inches. You will pay a little more for a color screen, but the extra cost is worth being able to discern important features. Many chartplotters are integrated, which means that the GPS receiver and the chartplotter are one unit. If you have a bigger boat and a bigger budget, chartplotters are available that do not have the GPS integrated within. These usually have larger and better screens. By using the chartplotter to display data from other devices such as radar, depth sounder, etc., the extra cost is justified.

What is Marine Technology ?

Marine technology is defined by WEGEMT (a European association of 40 universities in 17 countries) as "technologies for the safe use, exploitation, protection of, and intervention in, the marine environment." In this regard, according to WEGEMT, the technologies involved in marine technology are the following:naval architecture, marine engineering, ship design, ship building and ship operations; oil and gas exploration, exploitation, and production; hydrodynamics, navigation, sea surface and sub-surface support, underwater technology and engineering; marine resources (including both renewable and non-renewable marine resources); transport logistics and economics; inland, coastal, short sea and deep sea shipping; protection of the marine environment; leisure and safety. Marine Technologies LLC (MT) is a U.S.-based company dedicated to providing superior vessel control solutions to the international offshore and commercial shipping industries. MT products include dynamic positioning systems, integrated bridge systems and VSAT communications. The company is headquartered in Mandeville, Louisiana, with offices in Norway, Singapore and Brazil.