Laura Rautiainen

To avoid hazardous situations, it is important to be able to forecast the condition leading to anomalous propagation of electromagnetic signal. In this study, the operational weather forecasting model Harmonie-AROME used by the Finnish meteorological institute was utilized to assess the effects of model resolution on predicting atmospheric ducting conditions. Four separate model configurations were tested altering the vertical and horizontal resolution. The testing period (from 19th of June to 12th of July, 2022) included several occasions when anomalous propagation had been detected at Northern Baltic sea by the Utö coastal surveillance radar. The comparison against the observations show potential of predicting ducting conditions with numerical weather prediction model. At the same time the results reveal the limitations of the model in producing realistic vertical profiles of temperature and humidity especially near surface.

To avoid hazardous situations, it is important to be able to forecast the condition leading to anomalous propagation of electromagnetic signal. In this study, the operational weather forecasting model Harmonie-AROME used by the Finnish meteorological institute was utilized to assess the effects of model resolution on predicting atmospheric ducting conditions. Four separate model configurations were tested altering the vertical and horizontal resolution. The testing period (from 19th of June to 12th of July, 2022) included several occasions when anomalous propagation had been detected at Northern Baltic sea by the Utö coastal surveillance radar. The comparison against the observations show potential of predicting ducting conditions with numerical weather prediction model. At the same time the results reveal the limitations of the model in producing realistic vertical profiles of temperature and humidity especially near surface.

To avoid hazardous situations, it is important to be able to forecast the condition leading to anomalous propagation of electromagnetic signal. In this study, the operational weather forecasting model Harmonie-AROME used by the Finnish meteorological institute was utilized to assess the effects of model resolution on predicting atmospheric ducting conditions. Four separate model configurations were tested altering the vertical and horizontal resolution. The testing period (from 19th of June to 12th of July, 2022) included several occasions when anomalous propagation had been detected at Northern Baltic sea by the Utö coastal surveillance radar. The comparison against the observations show potential of predicting ducting conditions with numerical weather prediction model. At the same time the results reveal the limitations of the model in producing realistic vertical profiles of temperature and humidity especially near surface.

To avoid hazardous situations, it is important to be able to forecast the condition leading to anomalous propagation of electromagnetic signal. In this study, the operational weather forecasting model Harmonie-AROME used by the Finnish meteorological institute was utilized to assess the effects of model resolution on predicting atmospheric ducting conditions. Four separate model configurations were tested altering the vertical and horizontal resolution. The testing period (from 19th of June to 12th of July, 2022) included several occasions when anomalous propagation had been detected at Northern Baltic sea by the Utö coastal surveillance radar. The comparison against the observations show potential of predicting ducting conditionswith numerical weather prediction model. At the same time the results reveal the limitations of the model in producing realistic vertical profiles of temperature and humidity especially near surface.

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 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 34 % of the time for the 7 m antenna and 59 % of the time for the 30 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. Anomalous AIS observations were also associated with stronger and higher ducts; when the duct height was 59 m, the occurrence rates were 90 % and 95 % for the 7 and 30 m antenna, respectively.

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.

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.

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.

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.

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.