# grazingang

Grazing angle of surface target

## Syntax

`grazAng = grazingang(H,R)grazAng = grazingang(H,R,MODEL)grazAng = grazingang(H,R,MODEL,Re)`

## Description

`grazAng = grazingang(H,R)` returns the grazing angle for a sensor `H` meters above the surface, to surface targets `R` meters away. The computation assumes a curved earth model with an effective earth radius of approximately 4/3 times the actual earth radius.

`grazAng = grazingang(H,R,MODEL)` specifies the earth model used to compute the grazing angle. `MODEL` is either `'Flat'` or `'Curved'`.

`grazAng = grazingang(H,R,MODEL,Re)` specifies the effective earth radius. Effective earth radius applies to a curved earth model. When `MODEL` is `'Flat'`, the function ignores `Re`.

## Input Arguments

 `H` Height of the sensor above the surface, in meters. This argument can be a scalar or a vector. If both `H` and `R` are nonscalar, they must have the same dimensions. `R` Distance in meters from the sensor to the surface target. This argument can be a scalar or a vector. If both `H` and `R` are nonscalar, they must have the same dimensions. `R` must be between `H` and the horizon range determined by `H`. `MODEL` Earth model, as one of | `'Curved'` | `'Flat'` |. Default: `'Curved'` `Re` Effective earth radius in meters. This argument requires a positive scalar value. Default: `effearthradius`, which is approximately 4/3 times the actual earth radius

## Output Arguments

 `grazAng` Grazing angle, in degrees. The size of `grazAng` is the larger of `size(H)` and `size(R)`.

## Examples

Determine the grazing angle of a ground target located 1000 m away from the sensor. The sensor is mounted on a platform that is 300 m above the ground.

`grazAng = grazingang(300,1000);`

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### Grazing Angle

The grazing angle is the angle between a line from the sensor to a surface target, and a tangent to the earth at the site of that target.

For the curved earth model with an effective earth radius of Re, the grazing angle is:

${\mathrm{sin}}^{-1}\left(\frac{{H}^{2}+2H{R}_{e}-{R}^{2}}{2R{R}_{e}}\right)$

For the flat earth model, the grazing angle is:

${\mathrm{sin}}^{-1}\left(\frac{H}{R}\right)$

## References

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

[2] Ward, J. "Space-Time Adaptive Processing for Airborne Radar Data Systems," Technical Report 1015, MIT Lincoln Laboratory, December, 1994.