In this post we provide an overview of Automatic Identification System (AIS) Receivers – tracking systems that enable efficient space-based maritime vessel detection across the globe – and share details of various products on the global market – if you’re familiar with this technology and would like to skip straight to the product listings, please click here.
In 2004 the International Maritime Organization (IMO) adopted new requirements designed to make it easier for sea-going vessels to be clearly identified.
The requirements stated that all ships of a certain size and undergoing particular kinds of voyage should carry an Automatic Identification System (AIS) device that provides real-time information to other vessels and coastal authorities. These requirements refer to:
- All ships of 300 gross tonnage and upwards engaged on international voyages,
- All cargo ships of 500 gross tonnage and upwards not engaged on international voyages, and
- All passenger ships, irrespective of size.
In this article we take a look at how satellites are used to receive and transmit this information from/to such vessels, to enable precise maritime tracking in the most remote areas of the planet, and view commercially-available products from around the world.
About maritime AIS use
The IMO regulation specifies that the AIS on board the vessel needs to provide vital information about it’s characteristics and activity, such as:
- navigational status, and
- additional safety-related information.
These data must be provided automatically to appropriately equipped shore stations, as well as other ships and aircraft.
The AIS must also be capable of fast and accurate data exchange. It should be able to pick up the same type of information it transmits from other ships and exchange data with facilities on the shore.
The systems act as collision-avoidance and navigational aids. Messages sent via AIS can also be picked up by a very high frequency (VHF) receiver in-orbit, a system able to observe maritime activity over a wide area.
Space-based vs terrestrial AIS
The primary advantage of space-based AIS receivers over terrestrial AIS devices is the scale of coverage that can be achieved.
Each satellite can monitor a large area on its own and a network that features enough satellites in suitable orbits can effectively cover the entire surface of the planet for AIS signals.
This means that individual vessels, distributed fleets, or even entire sections of Ocean can be consistently monitored from space – removing the requirement for any terrestrial systems.
How space-based AIS functions
There are currently two methodologies in use for detection of AIS signals from space; on-board processing (OBP) and spectrum de-collision processing (SDP).
OBP involves the use of specialized receivers which, while much more sensitive, basically work in the same manner as terrestrial AIS receivers.
It doesn’t require special processing capabilities and is very effective in low density areas, such as the middle of the Pacific Ocean.
However one of OBP’s shortcomings is that the detection probability is significantly lower in areas of the satellite footprint that have high ship density – particularly at a level of 1,000 ships per footprint.
At this density the signals from individual vessels can start to collide with each other. Statistical analysis has shown that the first pass detection performance of OBP in such high dense areas is quite low and this means that a complete picture of the maritime domain often requires multiple passes.
In addition, if the traffic is very dense (over 2,500 vessels) then slot collisions will occur meaning messages cannot be resolved through OBP, and so gaining a complete maritime picture in such circumstances is impossible.
SDP involves the use of receivers capable of detecting and digitizing the RF spectrum for the AIS channels and then processing the raw spectrum files to control the noise floor and then reconstruct collided messages with highly specialized software algorithms.
First pass detection is very high, even in areas with a high ship density, and full maritime domain awareness can typically be achieved in as little as two passes.
Therefore, if the area of interest contains higher ship densities, SDP methodology is usually recommended in order to achieve detection at a level that will enable operational use of Satellite-AIS (S-AIS) (for further reading please see this exactEarth white paper [PDF]).
The challenge of AIS in space
The deployment of space-borne AIS receivers faces a variety of challenges stemming from the fact that the technology is primarily intended for sea-level reception.
One major concern is related to the self-organization principle of terrestrial AIS communication systems.
All exchanged messages transmitted from ships within the VHF range of 30-40 nm are synchronized, meaning that there are no AIS reports sent at the same time, at the same frequency. This guarantees the proper functioning of the system without any message loss.
An AIS receiver mounted on a satellite however sees several of these self organizing cells within its footprint (>3,000 km diameter).
Due to the fact that there is no synchronization between the cells, only within each cell, it’s likely that the satellite receives AIS messages from multiple vessels sent at the same time with the same frequency.
This can cause message collision resulting in message loss.
Another issue is the saturation of the satellite sensor due to the high volume of messages received, particularly in high density traffic areas such as the Mediterranean or the Baltic Sea.
Message collision and receiver saturation are known to be the main factors that affect the performance of an S-AIS device, measured as the Probability of Detection (PoD) of picking up an AIS position report transmitted by a vessel.
To meet these challenges and improve ship tracking capability from space advanced algorithms, antennas and frequency diversification have been used onboard space-based AIS systems.
AIS Receivers on the global marketplace
In this section, you can find a range of satellite AIS receivers available on the international market. These listings will be updated when new S-AIS receivers are added to the global marketplace for space at satsearch.co – so please check back for more or sign up for our mailing list for all the updates.
Click on any of the links or images below to find out more about the systems. You can also submit a request for a quote, documentation or further information on each of the products listed or send us a more general query to discuss your specific needs, and we will use our global networks of suppliers to find a system to meet your specifications.
The QubeAIS Receiver is a fully self-contained SDR-based AIS receiver suitable for LEO satellite missions. It weighs less than 55 g and uses less than 1 W during full load. The product has flight heritage from several missions including AAUSAT3 for which Aalborg University has public data. The system is designed to be easy to calibrate and is in-orbit configurable for 162 MHz or 156.8 MHz long-range AIS channels.
The Polaris 4-channel AIS Receiver is a fully self-contained software-defined radio receiver for the maritime VHF band, with integrated demodulators for reception of standard and long-range AIS messages. The system offers full AIS functionality within the typical size, weight and power constraints of a CubeSat – or can be used as an additional payload on larger LEO satellites. The system covers all AIS channels and supports two antenna inputs. It has a receive bandwidth up to 20 KHz per channel and a maximum input signal up to +10 dBm.
The STS300 CubeSat AIS Receiver – a 6-channel on-board processing (OBP) satellite AIS payload capable of receiving more than 1 million AIS messages per day. It covers all AIS channels in the maritime band (156 to 162 MHz) and has an input power level of 400 mW – 650 mW. The system weighs 180 g and has a data output of 115 kHz Asynchronous Serial, 3.3 Volt TTL.
The STS200 Satellite AIS Receiver – a space-qualified 6-channel S-AIS receiver for the collection and on-board processing of AIS messages.
A reconfigurable SDR-based receiver, designed to support simultaneous on-board AIS decoding and digital sampling. The ASR x50 features enhanced algorithms, multi-antenna support and a wide dynamic range, and is designed for a 7+ year lifetime. The system weighs 1.3 kg, has a frequency range of 156 — 163 MHz and power consumption of 4.5 — 6.5 W.
The AIS-MS03 by Honeywell Aerospace Inc.
A low-power multi-mode AIS receiver product that has been optimized for the highest first pass detection rate of marine traffic from space. The system features a direct sampling receiver and is capable of performing simultaneous On-Board Processing (OBP) and raw spectrum capture for On-Ground Processing (OGP), while the on-board memory allows storage of data from multiple orbits. This functionality is complemented by the ability to reprogram the equipment in-orbit with the aim of updating its algorithms and improving performance characteristics.
Suitable for vessel tracking in dense maritime zones. The system is designed with an algorithm available on low-power FPGA platforms and to reduce latency in data detection and fusion. It eliminates downlink Doppler compensation with reduced downlink power and bandwidth requirements, and supports base-band waveform capture.
Heliox Cosmos manufactures APRS (Automatic Packet Reporting Systems) that enable real-time repeat or forward positioning and data. The systems pick up vessel positions using an AIS A/B channels transponder and are suitable for a variety of applications alongside maritime tracking including ecological monitoring, wide area power grid management and ocean current tracking. The systems have a 5 V power supply, an operating temperature range of -20 °C to + 80 °C. The devices also feature an IPX RF connector and a UART TTL standalone data interface.
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