Abstract
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.
Highlights
The two Norwegian microsatellites NorSat-1 and NorSat-2 were launched 14 July 2017 [1], doubling the number of own assets for the satellite-based AIS data collection for the services provided by the Norwegian Coastal Administration
The AIS messages are forwarded to the Satellite Control Centre (SCC) at Statsat AS in Oslo, and to the Norwegian Coastal Administration in Haugesund
Looking at the results from the North Atlantic, an improvement in number of messages can clearly be seen, while the improvement in number of ships is marginal over a 24-h period, indicating that the daily ship detection probability by the AISSat-1 generation AIS receiver was good from the start
Summary
The two Norwegian microsatellites NorSat-1 and NorSat-2 were launched 14 July 2017 [1], doubling the number of own assets for the satellite-based AIS data collection for the services provided by the Norwegian Coastal Administration. The NorSats carry the fourth-generation space-AIS receiver from Kongsberg Seatex AS, the ASR x50 developed under the ESA ARTES program using commercial off-theshelf components, efficient evaluation and testing schemes, and advanced technological solutions [2] It is known as the Novel SAT-AIS (NAIS) receiver [3] having high sensitivity, improved decoder performance, multi-antenna, and. This paper investigate the improvements made globally as well as in selected areas in terms of the number of messages received and number of ships detected It quantifies the performance increase through three types of developments: the receiver electronics and the algorithms, the antenna diversity, and the multi-channel architecture giving continuous operation on all four AIS channels
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