As the International Space Station circles the Earth, it is tracking individual ships crossing the seas beneath. An ESA investigation hosted in the European Columbus module has been testing the viability of monitoring global maritime traffic from the Station’s orbit hundreds of kilometres up since June 2010.

The ship-detection system being tested is based on the Automatic Identification System, or AIS, the marine equivalent of the air traffic control system. Astronauts were instrumental in enabling the COLAIS experiment, which is an in-orbit demonstration project from ESA’s General Support Technology Programme.

The two operational phases with NORAIS, which is operated by FFI/Norway, have been extremely successful, with data telemetry received by the N-USOC, in Trondheim, Norway, via ESA’s Columbus Control Centre in Germany. Data has been received by NORAIS in almost continuous operation, and all modes of operation have worked extremely well. On a good day, approximately 400,000 ship position reports are received from more than 22,000 different ship identification numbers (Maritime Mobile Service Identity, or MMSI). See Figure 1.

Figure 1: Ship positions reports received with the NORAID receiver during 24 hours, 29th June 2010 (Credit: FFI)

Figure 1: Ship positions reports received with the NORAIS receiver during 24 hours, 29th June 2010 (Credit: FFI)

The NORAIS receiver has a sample mode that can collect the raw signal, digitize it and send it to the ground for analysis of signal quality; this is proving very helpful in making additional improvements/ refinements to the system. Several hundred data sets have been collected and processed with new candidate algorithms for next generation receivers.

From the assessment of these data sets, an updated version of the decoder algorithm has been developed. The development benefits from the investigations of the sampled data and ongoing work in other ESA projects. The firmware was uploaded to the NORAIS Receiver through the station’s communications network. This upgrade #1 (“NORAIS Receiver FPGA firmware v18”), was activated on 20 January 2012.

The on-orbit data of the NORAIS Receiver v18 have been analysed since and show very good results. The teams are confident in the operation and performance of v18 and have now preliminary results of the comparison of the performance of the upgraded NORAIS Receiver (v18) relative to the version operated prior to the upgrade (v16).

The performance has been studied as the average number of decoded messages per day for the current upgrade v18 of the firmware and the original NORAIS receiver software. The improvement is the ratio of these numbers (so average numbers of messages per day before the upgrade divided by number of messages after the upgrade). The number of messages from ships in various geographic areas shows a variation in the ratio of messages from 1.2 to 2.0, whereas the ratio of MMSI’s ranges from 1.1 to 1.9. The improvement in the Mediterranean is almost a factor of 2.0 in number of messages, and more than 1.6 in number of distinct ships per day. The improvement in other high-traffic zones, at the Gulf of Mexico and East Asia, is even higher. The plot below shows the ratio of the daily average number of messages and unique MMSI’s for some ocean areas. Refer to Figure 2.

Figure 2: Ratio of the average number of messages received per day (after upgrade / before upgrade) in selected ocean areas.

Figure 2: Ratio of the average number of messages received per day (after upgrade / before upgrade) in selected ocean areas.

We use the Mediterranean to illustrate the increased performance. The ship traffic in the Mediterranean is of special interest to Europe, since it is one of the approaches to Europe and partly European waters. The ratios calculated for this region are shown with some plots. See Figures 3 and 4.

Figure 3: Ship positions on 23rd January 2012 (DOY023) shown in the plot below has 1245 messages, which is close to the mean value for v18, and the number of MMSI’s is 744.

Figure 3: Ship positions on 23rd January 2012 (DOY023) shown in the plot below has 1245 messages, which is close to the mean value for v18, and the number of MMSI’s is 744.

Figure 4: Ship positions on 5th December 2011 (DOY339) shown in the plot below has 611 messages, close to the mean for v16, and the number of MMSI’s is 453. The difference in the numbers is visible both in the ship density and also that more ships are detected in the northern part of the Mediterranean.

Figure 4: Ship positions on 5th December 2011 (DOY339) shown in the plot below has 611 messages, close to the mean for v16, and the number of MMSI’s is 453. The difference in the numbers is visible both in the ship density and also that more ships are detected in the northern part of the Mediterranean.

The VESSEL Identification System team is of course delighted with the great results of this upgrade. In fact, they are already working on a next upgrade!