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Norway currently operates four satellites with Automatic Identification System (AIS) receivers. The first-generation satellites, AISSat-1 and AISSat-2, are equipped with a two-channel, single-antenna AIS receiver, while NorSat-1 and NorSat-2 are equipped with an improved AIS receiver capable of decoding on all four AIS channels and using the two antennas installed on the NorSat satellites. This paper aims to investigate the ship tracking performance enhancement realised by the technology improvements of antenna diversification, frequency diversification, and advanced algorithms. The ship tracking capability of the NorSat satellites is presented and shown to yield a significant improvement, up to a 20% point increase, over the first AISSat generation ship tracking capability. A further 20% point increase is achieved in select areas using frequency diversity introduced in the AIS system since the development of the AISSat satellites. In addition, NorSat-1 detected 34% more vessels than AISSat-2 over the same timeframe. The contribution to the performance improvement from the incremental improvements in decoding algorithms, antenna diversity, and frequency diversity is indicated in the results. The results indicate that, in the short term, upgrading to the latest algorithms, low noise electronics, and taking advantage of antenna diversity is the greatest performance enhancer. In the medium and long term, the frequency diversity likely yields the greatest performance enhancement.

This paper presents a trial carried out in the Malangen area close to Tromsø city in the north of Norway in September 2010. High resolution Synthetic Aperture Radar (SAR) images from RADARSAT-2 were used to analyse how SAR images and cooperative reporting can be combined. Data from the Automatic Identification System, both land-based and space-based, have been used to identify detected vessels in the SAR images. The paper presents results of ship detection in high resolution RADARSAT-2 Standard Quad-Pol images, and how these results together with land-based and space-based AIS can be used.

Two Norwegian AIS-satellites, NorSat-1 and NorSat-2, were launched in July 2017. Both are equipped with the ASR x50, the latest space-AIS receiver developed by Kongsberg Seatex AS, offering advanced signal processing and continuous operation on all four AIS channels. The NorSat-satellites collect ~ 1.5 million messages from ~ 50,000 ships per day (24 h) each, which is a factor ~ 2.8 increase in the number of messages compared to the ASR 100 on-board AISSat-1 and AISSat-2. The improvements of the AIS-satellites can be attributed to three developments: the performance of the receiver, the use of antenna diversity, and the use of frequency channel diversity. Daily statistics for February 2018 over the Mediterranean Sea illustrate the improvements: The median value of the number of messages received with NorSat-1 using only one antenna is 2.3 times higher than for AISSat-1. When both NorSat-1 antennas are used, the improvement factor becomes 4.1, and finally, when two additional receiver channels are used to collect long-range AIS messages, the total improvement becomes 8.2 times. In terms of ships detected, the factors are 1.8, 2.7, and 4.4 for the respective steps. Long-range AIS messages amount to just 5% of the total AIS messages received by NorSat-1 in August 2017, but it allows to detect 20% more ships on a global scale, and as much as 10 times more ships in a the high-traffic area in the North Sea.