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AIS Satellite Receivers
|Author||Topic: AIS Satellite Receivers|
posted 08-02-2012 12:19 AM ET (US)
exactEarth is a company from Cambridge, Ontario, Canada that is in the business of collecting data from commercial ships by receiving their AIS broadcasts. The significant distinction is that exactEarth is able to receive AIS broadcasts in near-real-time from ships located just about anywhere on the planet. They do this by using AIS receivers in space carried on micro satellites they themselves own. In late July, 2012, they launched their latest AIS receiver in orbit, the COM DEV EV-1 satellite.
The EV-1 satellite was carried into a sun-synchronous polar orbit of 800-km by a Soyuz-FG launch vehicle from the Baikonur Cosmodrome in Kazakhstan. It is the fifth AIS satellite for exactEart. The AIS satellites are placed into a North-South polar orbit. As the satellites orbit, the earth turns underneath them. The result is that a single satellite covers all areas of the earth in about a 12-hour period. Eventually exactEarth plans to have many satellites in orbit, which should allow coverage of all of the earth with only 90-minutes between fly-over of any one point.
A micro satellite is a very small satellite, typically with a weight of 100-kg (220-lbs) at most. The small size and low weight of the micro satellites drastically reduce the cost of building and orbiting them. The time to design and build them is also much shorter than for traditional and larger satellites.
The COM DEV EV-1 AIS micro satellite was built by Surrey Satellite Technology Ltd. of Guildford in the United Kingdom. The AIS micro satellite is based on the Surrey SSTL-100 platform, augmented with additional solar panels to provide added power to operate the AIS receivers. Although the cost of a micro satellite is much less than larger spacecraft, the base price of a SSTL-100 micro satellite is still about ten-million dollars. The SSTL-100 platform weighs about 15-kg (33-lbs).
The AIS micro satellites are designed to receive AIS transmission from ships. Ships transmit their position, speed, and heading data using AIS transponders that cooperate with each other in a self-organized network to avoid data collisions in transmission. The typical range of transponders on the open sea is only about 50-miles. Thus the self-organizing networks can be considered to be somewhat localized to the ships that are in range of each other. On the other hand, the AIS micro satellite orbiting overhead at a range of several hundred miles can receive transmissions from ships that may be out of range of each other. Their broadcasts may not be self-organized to avoid collision of data during transmission. This means the AIS receivers on the satellite need specialized technology that can keep AIS transmission separate, even if they are overlapping or colliding with each other. exactEarth says they have developed such technology.
The AIS micro satellites also must store the data until it can be forwarded by S-band and C-band microwave downlink to Earth stations. exactEarth is operating a network of Earth stations, which then forward the data to central servers for storage and analysis. The data downlink can occur only when the micro satellite is in range of an appropriate Earth station. The down-link access is typically limited to about a ten minute period as the satellite flies overhead. The data collected must be sent in this short period, so a high-speed data link is needed. Currently there are downlink stations in the Northern Hemisphere at Svalbard, Norway and Guilford, UK, and at other unspecified locations. Addition of downlink stations in the Southern Hemisphere is planned. At full deployment, the downlink data should not be older than about 15-minutes.
In this most unusual and high-tech manner exactEarth has been able to collect near-real-time data about ships at sea on a global basis. Their business is then to offer the data for sale to private parties.
This is an interesting business model in that the transmission of the information is required by international agreement. All commercial ships above a minimum size must be equipped with transponders and must transmit the data about their position, course, and speed. The system was initially designed as a collision avoidance system to improve safety at sea. With the development of AIS micro satellites and their operation by a private for-profit company, the ship data being sent is now being gathered, recorded, organized, and offered for sale. One has to wonder if when the system were first envisioned and proposed if anyone foresaw the possibilities of it becoming the basis for a global marine tracking system.
posted 10-21-2012 12:05 PM ET (US)
The exactEarth AIS micro-satellite EV-1 that was successfully launched in July of 2012 has just completed its testing phase. Peter Mabson, President of exactEarth, released the following comments a few days ago:
Most notable is the announcement that EV-1 has made a significant improvement in the detection rate of AIS transmissions compared to previous generation satellite receiving systems. Twice as many ship transmissions are being detected now.
The EV-1 AIS micro satellite is expected to be in full operation in November, pending completion of a few more deployment and commissioning tasks.
posted 12-21-2012 11:08 AM ET (US)
In late November (2012) exactEarth reported that their newest AIS micro-satellite, the exactVeiw-1 or EV-1, had entered into commercial service. The EV-1 has shown improved sensitivity compared to previous AIS satellites, and it is reported to be detecting 45,000 marine mobile service identities (MMSI's) per day. In doing so it has doubled the number of unique MMSI's detected daily to approximately 90,000 vessels.
The improved sensitivity of the EV-1 allows it to detect more AIS Class-B transponders. Class-B transponders are carried on non-mandatory AIS vessels and are lower-power transmitters. Class-B AIS signals are transmitted at 2-Watts compared to 12.5-Watts for Class-A transponders, about an 8-dB reduction in signal. The EV-1 data showed a 30-percent increase in the number of Class-B transponders detected.
exactEarth recently published a chart showing more than 400 vessels with Class-B AIS transponders were making a transit across the Atlantic Ocean. The number of vessels was perhaps augmented by the coincidence with a cruising sailor rally event, the Atlantic Rally for Cruisers, starting in Las Palmas, Canary Islands, and heading for Saint Lucia in the Caribbean.
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