Coverage Maps FAQ
What information does a coverage map provide?
A coverage map illustrates all the points, where updates for aircraft are likely to be received at certain altitude. The probability of receiving an update for an aircraft is determined by the chance of obtaining at least one position update within a designated time frame. Locations where the probability of receiving an update exceeds a certain threshold are considered to be covered.
To compute the coverage map, three key parameters are utilized:
- Considered Altitude: This is the height above ground level for which the coverage assessment is carried out. A coverage map illustrates whether an aircraft is likely to be detected at a certain location at that altitude.
- Time Interval (TI): This denotes the predetermined time span within which an aircraft update is expected. A standard value for TI is 4 seconds.
- Probability Update (PU): The coverage map is derived by estimating the likelihood of obtaining a position update within the time interval TI for an aircraft at the specified altitude. If this probability surpasses the PU threshold, the location is classified as covered at that altitude. Common PU values are 90% and 97%.
How is a coverage map generated?
1) Initially, the radio reception capabilities of each receiver are assessed using air traffic data. This assessment is conducted by comparing the actual number of detections to the expected messages transmitted by the aircraft's transponder, which helps determine how effectively each receiver captures signals from the transponders.
2) The subsequent step involves creating a line of sight map for each receiver, utilizing the receiver's geographical position along with a digital surface model of the Earth.
3) Finally, the radio performance models, which likely depict the characteristics of signal propagation, are merged with the line of sight maps from all operational receivers. This combination yields a detailed coverage map.
Ultimately, the coverage map synthesizes information on receiver functionality, visibility conditions, and radio propagation models to showcase areas with stable reception.
What does it signify when there is no coverage displayed for a particular cell?
When a location or cell is identified as lacking coverage, it suggests that the likelihood of receiving updates for an aircraft at that altitude is beneath the threshold PU. Still, some aircraft might remain visible in areas considered uncovered due to factors such as signal strength, terrain, or other variables. This happens because coverage maps are determined by probabilities and thresholds, not by definitive measures.