MARITIME – ELECTRICAL & ELECTRONIC CALCULATOR
Ais Target Range
A precise tool.
What is the Ais Target Range & How does it work?
Automatic Identification System (AIS) transponders operate on VHF maritime channels, which are fundamentally limited by the radio‑line‑of‑sight principle. The curvature of the Earth blocks the direct path once the distance exceeds the geometric horizon, so the height of the transmitting and receiving antennas becomes the dominant factor in determining range.
The line‑of‑sight distance can be approximated with a simple empirical formula that incorporates a refraction coefficient k (≈ 1.33 for standard atmospheric conditions). By inserting the antenna height h (in metres) into the square‑root term, the formula yields the maximum distance d in kilometres that a VHF signal, such as an AIS broadcast, can travel before it is lost to the horizon.
When two vessels exchange AIS data, each contributes its own horizon. The total usable range is therefore the sum of the individual horizons from the own ship’s antenna and the target ship’s antenna. This additive model provides a quick, yet reliable, estimate for planning safe navigation corridors.
d = 3.57 sqrt{k cdot h_1} + 3.57 sqrt{k cdot h_2},text{km}
d = maximum line‑of‑sight distance (km)
Parameters
Result
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Frequently Asked Questions
What is the formula used to calculate AIS target range?
The formula approximates line-of-sight distance with a refraction coefficient k (≈1.33).
How does antenna height affect AIS range?
Higher antennas increase the effective range by extending the line of sight over obstacles.
What is the significance of the refraction coefficient in AIS calculations?
The refraction coefficient accounts for atmospheric conditions that bend radio waves, affecting the calculated range.
Can I calculate the maximum distance an AIS signal can travel?
Yes, by inputting the antenna heights and using the formula with k ≈ 1.33, you can estimate the maximum range.
How does curvature of the Earth impact AIS communication?
The Earth’s curvature limits direct line-of-sight, so higher antennas are needed to maintain communication over longer distances.
What factors should I consider when setting up AIS transponders for optimal range?
Consider the height of transmitting and receiving antennas, as well as atmospheric conditions affecting refraction.
Is there a way to increase the range of AIS signals without changing antenna heights?
No, increasing signal power or using directional antennas might help slightly, but antenna height is the primary factor for range.
Results are for informational purposes only and do not constitute professional advice.