# Documentation

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# horizonrange

## Syntax

```Rh = horizonrange(H) Rh = horizonrange(H,Re) ```

## Description

`Rh = horizonrange(H)` returns the horizon range of a radar system `H` meters above the surface. The computation uses an effective earth radius of approximately 4/3 times the actual earth radius.

`Rh = horizonrange(H,Re)` specifies the effective earth radius.

## Input Arguments

 `H` Height of radar system above surface, in meters. This argument can be a scalar or a vector. `Re` Effective earth radius in meters. This argument must be a positive scalar. Default: `effearthradius`, which is approximately 4/3 times the actual earth radius

## Output Arguments

 `Rh` Horizon range in meters of radar system at altitude `H`.

## Examples

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Determine the range to horizon for an antenna that is 30 m high.

`Rh = horizonrange(30)`
```Rh = 2.2553e+04 ```

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### Horizon Range

The horizon range of a radar system is the distance from the radar system to the earth along a tangent. Beyond the horizon range, the radar system detects no return from the surface through a direct path.

The value of the horizon range is:

`$\sqrt{2{R}_{e}H+{H}^{2}}$`

where Re is the effective earth radius and H is the altitude of the radar system.

## References

[1] Long, Maurice W. Radar Reflectivity of Land and Sea, 3rd Ed. Boston: Artech House, 2001.

[2] Skolnik, M. Introduction to Radar Systems, 3rd Ed. New York: McGraw-Hill, 2001.