grazingang

Grazing angle of surface target

Since R2021a

Syntax

grazAng = grazingang(H,R)

grazAng = grazingang(H,R,MODEL)

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

grazAng = grazAng = grazingang(___,TargetHeight=TGTHT)

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) also specifies the earth model used to compute the grazing angle. MODEL is either "Flat" or "Curved".

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

grazAng = grazAng = grazingang(___,TargetHeight=TGTHT) also specifies the target height, TGTHT above the surface as either a scalar or a vector. If any combination of ht, 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.

Examples

Compute Grazing Angle

Determine the grazing angle (in degrees) of a path to a ground target located 1.0 km from a sensor. The sensor is mounted on a platform that is 300 m above the ground.

grazAng = grazingang(300,1.0e3)

grazAng = 
17.4544

Input Arguments

H — Height of the sensor above the surface

scalar | vector

Height of the sensor above the surface in meters, specified as a scalar or a vector. If both H and R are nonscalar, they must have the same dimensions.

Data Types: double

R — Distance from the sensor to the surface target

scalar | vector

Distance from the sensor to the surface target in meters, specified as 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.

Data Types: double

MODEL — Earth model

"Curved" (default) | "Flat"

Earth model, specified as one of "Curved" or "Flat".

Data Types: char | string

Re — Effective earth radius

effearthradius (default) | positive scalar

Effective earth radius in meters, specified as a positive scalar. You can use effearthradius to compute the effective radius. The function provides a default value approximately 4/3 times the actual earth radius

Example: 6.4e6

Data Types: double

TGTHT — Target height above surface

0 (default) | scalar | vector

Target height above surface in meters, 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.

Data Types: double

Output Arguments

grazAng — Grazing angle

scalar | vector

Grazing angle in degrees returned as a scalar or vector. If grazAng is a vector, it has the same dimensions as the nonscalar inputs to grazingang.

More About

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 R_e, the grazing angle is:

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

For the flat earth model, the grazing 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