the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Studying anomalous propagation over marine areas using an experimental AIS receiver set-up
Abstract. Automatic Identification System (AIS) is a wireless communication system used by vessels to exchange real-time information with each other and with coastal authorities, enhancing situational awareness and maritime safety. Consequently, safety at sea depends on reliable signal transmission, which can be disrupted by anomalous signal propagation. In particular, tropospheric ducting can extend the AIS antenna horizon, allowing messages to be received over greater distances than under standard conditions. To study the behaviour of the AIS signal under standard and anomalous propagation conditions, 1-year of AIS-observations were collected from two antennae at 7 m and 30 m heights above the mean sea level on the Utö Island in the Baltic Sea. The AIS antennae were co-located with mast-mounted measurements of temperature and humidity. This allows for studying the AIS signal propagation alongside observed refractivity profiles. The AIS over-the-horizon observations occurred 59 % of the time for the 30 m antenna and 34 % of the time for the 7 m antenna, mainly during the spring and summer months. A strong diurnal cycle was observed in the Archipelago Sea, north of Utö, while no diurnal cycle was observed in the open sea region south of Utö. During periods of anomalous signal propagation, the AIS messages were received from farther away, from up to 600 km from Utö and the observed received signal strength decayed slower with distance, indicating reductions in propagation losses due to ducting. The anomalous AIS observations were also found to coincide with the stronger and higher observed ducts.
- Preprint
(5488 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 23 Sep 2025)
-
RC1: 'Comment on egusphere-2025-1790', Alex Chartier, 11 Aug 2025
reply
First review of: Studying anomalous propagation over marine areas using an experimental AIS receiver set-up
Thanks for an interesting manuscript. I have the following comments, but defer to tropospheric experts regarding the significance of the results.
- What is the distribution of propagation distances observed? Can you show a histogram of distances to illustrate the ‘break point’ between normal and anomalous propagation? The selected criterion (95th percentile of maximum distance) seems ad-hoc and vulnerable to variations in the distribution of ships with relation to the receiver station (as noted by the authors between lines 325-30). Why not use a simple distance cutoff (e.g. at least X counts >300 km indicates anomalous propagation)?
- It is not obvious (at least to me) whether the results are in keeping with what is expected from current atmospheric propagation models. Additionally, the ducting analysis is restricted to local conditions at the receiver site (Utö). These two issues could be remedied by comparing the results to duct strengths calculated from meteorological reanalysis data.
- Parts of the introduction seem to make a false dichotomy between VHF and AIS (e.g. 38-40, 52-53). Consider rephrasing.
Line-by-line comments as follows:
14-15: Provide some statistical metric to support the claim that “anomalous AIS observations were also found to coincide with the stronger and higher observed ducts”
41: Specify ‘at distances of less than 1000 km.’
53: Given the separate categorization of (1) AIS and (2) VHF, Chartier et al. (2022) belongs in the first group rather than the second.
223 (and elsewhere): Consider using a different term than ‘horizon’. The manuscript makes sense if ‘horizon’ is interpreted as ‘horizon of observability’, but the most natural interpretation is 'the line at which the earth's surface and the sky appear to meet.’
Citation: https://doi.org/10.5194/egusphere-2025-1790-RC1
Viewed
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
498 | 9 | 5 | 512 | 13 | 15 |
- HTML: 498
- PDF: 9
- XML: 5
- Total: 512
- BibTeX: 13
- EndNote: 15
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1