Documentation

# depressionang

Depression angle of surface target

## Syntax

depAng = depressionang(H,R)
depAng = depressionang(H,R,MODEL)
depAng = depressionang(H,R,MODEL,Re)

## Description

depAng = depressionang(H,R) returns the depression angle from the horizontal at an altitude of H meters to surface targets. The sensor is H meters above the surface. R is the range from the sensor to the surface targets. The computation assumes a curved earth model with an effective earth radius of approximately 4/3 times the actual earth radius.

depAng = depressionang(H,R,MODEL) specifies the earth model used to compute the depression angle. MODEL is either 'Flat' or 'Curved'.

depAng = depressionang(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

 depAng Depression angle, in degrees, from the horizontal at the sensor altitude toward surface targets R meters from the sensor. The dimensions of depAng are the larger of size(H) and size(R).

## Examples

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Calculate the depression angle for a ground clutter patch that is 1.0 km away from a sensor. The sensor is located on a platform 300 m above the ground.

depang = depressionang(300,1000)
depang = 17.4608

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### Depression Angle

The depression angle is the angle between a horizontal line containing the sensor and the line from the sensor to a surface target.

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

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

For the flat earth model, the depression 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.