Use this tool to estimate radar horizon distance, combined line of sight, curvature drop, safe operating range, and visibility status after margin. It supports metric and imperial inputs, custom Earth radius, and custom atmospheric refraction through the k-factor.
Calculator inputs
Formula used
The calculator uses the geometric horizon expression for both radar and target heights, then adds the two horizon distances.
d = √(2 × k × R × h + h²)
- d = horizon distance for one object.
- k = effective Earth radius factor for refraction.
- R = Earth radius.
- h = object height above the local surface.
Combined line of sight:
Dtotal = dradar + dtarget
Adjusted planning range after margin:
Dsafe = Dtotal × (1 − margin / 100)
Curvature drop at a chosen path length:
drop = range² / (2 × k × R)
How to use this calculator
- Select metric or imperial inputs.
- Enter radar antenna height and target height.
- Keep the default Earth radius unless you need a custom model.
- Use k = 1.333333 for a common standard-atmosphere assumption.
- Add a safety margin to reflect planning uncertainty or terrain allowance.
- Enter a desired operating range to test whether it fits the adjusted LOS.
- Choose the chart resolution, then submit the form.
- Review the result cards, graph, and export buttons.
Example data table
| Radar height (m) | Target height (m) | k-factor | Combined LOS (km) | LOS with 10% margin (km) |
|---|---|---|---|---|
| 15 | 5 | 1.333 | 25.180 | 22.662 |
| 35 | 12 | 1.333 | 38.663 | 34.797 |
| 60 | 20 | 1.250 | 48.762 | 43.885 |
| 120 | 35 | 1.333 | 69.537 | 62.584 |
Frequently asked questions
1) What does radar line of sight mean?
It is the maximum geometric range where a radar and target can still see each other over Earth curvature, before terrain, clutter, ducting, or system losses are considered.
2) Why does height matter so much?
Higher antennas and higher targets both extend the horizon. Even modest mast increases can noticeably improve visible range because the square-root relationship grows steadily with height.
3) What is the k-factor?
The k-factor adjusts Earth curvature to reflect atmospheric refraction. A larger value bends radio paths farther, increasing effective visibility. A common planning value is about 4/3.
4) Is this the same as detection range?
No. Detection range also depends on power, frequency, target size, noise, pulse settings, weather, and processing. This calculator only estimates the geometric visibility limit.
5) Why include a safety margin?
A margin creates a more conservative planning range. It helps account for uncertain refraction, local terrain variation, mast flex, and practical deployment differences.
6) What does curvature drop show?
It estimates how much the Earth surface falls away from a straight tangent-like path over the chosen distance, after the selected refraction adjustment is applied.
7) Can I use custom Earth radius values?
Yes. That option helps with alternate modelling, educational scenarios, or sensitivity checks. Keep units consistent with the selected metric or imperial system.
8) Does terrain blocking appear in the graph?
No. The graph isolates curvature, refraction, target height, and margin effects. Terrain screening, buildings, vegetation, and sea state require a separate path profile model.