depressionang

Depression angle of surface target

Syntax

depAng = depressionang(H,R)
depAng = depressionang(ht,r,MODEL)
depAng = depressionang(H,R,MODEL,Re)
depAng = depressionang(___,'TargetHeight',TGTHT)


Description

depAng = depressionang(H,R) returns the depression angle from the horizontal at an altitude of R 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(ht,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.

depAng = depressionang(___,'TargetHeight',TGTHT) specifies the target height, TGTHT above the surface as either a scalar or a vector. If any combination of H, R, and TGTHT are vectors, then the dimensions must be equal. r must be greater than or equal to the absolute value of the difference of ht and TGTHT.

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 TGTHT.
MODEL	Earth model, as one of | 'Curved' | 'Flat' |. Default: 'Curved'
Re	Effective earth radius in meters. This argument must be a positive scalar value. You can used effearthradius to compute the effective radius. Default: effearthradius, which is approximately 4/3 times the actual earth radius
TGTHT	Target height above surface, specified as a scalar or vector. If any combination of H, R, and TGTHT are vectors, then their sizes must be equal. R must be greater than or equal to the absolute value of the difference of H and TGTHT. A surface target has a TGTHT of zero. Default: 0

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(ht) and size(r).

Examples

Compute Depression Angle

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

More About

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 R_e, the depression angle is:

$${\sin }^{-1}\left(\frac{H^2+2H{R}_e+R^2}{2R(H+R_e)}\right)$$

For the flat earth model, the depression angle is:

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

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.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

Does not support variable-size inputs.

Version History

Introduced in R2021a