towerpy.georad.georef_rdata

Towerpy: an open-source toolbox for processing polarimetric radar data.

Functions

cart2pol(x, y)	Transform Cartesian coordinates to Polar.
pol2cart(rho, theta)	Transform polar coordinates to Cartesian.
height_beamc(elev_angle, rad_range[, e_rad, std_refr])	Calculate the height of the centre of the radar beam above Earth's surface.
cartesian_distance(elev_angle, rad_range, hbeam[, ...])	Compute the distance (arc length) from the radar to the bins.
ppi_georef(rparams[, georef, polarc_exist, elev, ...])	Create georeferenced grid for PPI radar scans.

Module Contents

towerpy.georad.georef_rdata.cart2pol(x, y)

Transform Cartesian coordinates to Polar.

Parameters

x, yarray

Cartesian coordinates

Returns

rhoarray

Radial coordinate, rho is the distance from the origin to a point in the x-y plane.

thetaarray

Angular coordinates is the counterclockwise angle in the x-y plane measured in radians from the positive x-axis. The value of the angle is in the range [-pi, pi].

towerpy.georad.georef_rdata.pol2cart(rho, theta)

Transform polar coordinates to Cartesian.

Parameters

rhoarray

Radial coordinate, rho is the distance from the origin to a point in the x-y plane.

thetaarray

Angular coordinates is the counterclockwise angle in the x-y plane measured in radians from the positive x-axis. The value of the angle is in the range [-pi, pi].

Returns

x, yarray

Cartesian coordinates.

towerpy.georad.georef_rdata.height_beamc(elev_angle, rad_range, e_rad=6378, std_refr=4 / 3)

Calculate the height of the centre of the radar beam above Earth’s surface.

Parameters

elev_anglefloat

Radar elevation angle in degrees.

rad_rangearray

Range from the radar in kilometres.

e_radfloat, optional

Effective Earth’s radius. The default is 6378.

std_refrfloat, optional

Standard refraction coefficient. The default is 4/3.

Returns

harray

Height of the centre of the radar beam in kilometres.

Notes

The beam height above sea level or radar level for a standard atmosphere is calculated by adapting equation (2.28b) in [1]_:

\(h = \sqrt{r^2+(\frac{4}{3} E_r)^2+2r(\frac{4}{3} E_r)\sin\Theta}-\frac{4}{3} E_r\)

Where:

h : height of the centre of the radar beam above Earth’s surface

r : radar range to the targets in kilometres.

\(\Theta\) : elevation angle of beam in degree

\(E_r\) : effective Earth’s radius [approximately 6378 km]

References

[1]

Doviak, R., & Zrnic, D. S. (1993). Electromagnetic Waves and Propagation in Doppler Radar and Weather Observations (pp. 10-29). San Diego: Academic Press, Second Edition. https://doi.org/10.1016/B978-0-12-221422-6.50007-3

towerpy.georad.georef_rdata.cartesian_distance(elev_angle, rad_range, hbeam, e_rad=6378, std_refr=4 / 3)

Compute the distance (arc length) from the radar to the bins.

Parameters

elev_anglefloat

Radar elevation angle in degrees.

rad_rangearray

Range from the radar in kilometres.

hbeamfloat

Height of the centre of the radar beam in kilometres.

e_radfloat, optional

Effective Earth’s radius. The default is 6378.

std_refrfloat, optional

Standard refraction coefficient. The default is 4/3.

Returns

s: array

Distance (arc length) from the radar to the bins in kilometres.

Notes

The distance in Cartesian coordinates is calculated by adapting equations (2.28b and 2.28c) in [1]_:

\(h = \sqrt{r^2+(\frac{4}{3} E_r)^2+2r(\frac{4}{3} E_r)\sin\Theta}-\frac{4}{3} E_r\)

\(s = \frac{4}{3} E_r * arcsin(\frac{r*cos(\Theta)}{\frac{4}{3} E_r+h})\)

References

[1]

Doviak, R., & Zrnic, D. S. (1993). Electromagnetic Waves and Propagation in Doppler Radar and Weather Observations (pp. 10-29). San Diego: Academic Press, Second Edition. https://doi.org/10.1016/B978-0-12-221422-6.50007-3

towerpy.georad.georef_rdata.ppi_georef(rparams, georef=None, polarc_exist=True, elev=0.5, gate0=0, gateres=250)

Create georeferenced grid for PPI radar scans.

Parameters

rparamsdict

Radar parameters dictionary. Must contain:

• ‘nrays’ : int, number of rays

• ‘ngates’ : int, number of range gates

• ‘beamwidth [deg]’ : float, beamwidth in degrees

georefdict, optional

Existing georeference dictionary with keys ‘azim [rad]’, ‘elev [rad]’, ‘range [m]’. Required if polarc_exist=True.

polarc_existbool

If True, polar coordinates (range, azimuth, elevation) are read directly from the georef attribute. If False, synthesise elevation, azimuth, and range. The default is True

elevfloat

Elevation angle in degrees (used if polarc_exist=False). The default is 0.5

gate0float

Starting range gate in metres (used if polarc_exist=False). The default is 0

gateresfloat

Gate resolution in metres (used if polarc_exist=False). The default is 250

Returns

geogriddict

Dictionary containing georeferenced arrays:

• ‘grid_rectx’, ‘grid_recty’ : Cartesian grid coordinates in kilometres

• ‘beam_height [km]’ : beam centre heights in kilometres

• ‘beambottom_height [km]’ : beam bottom heights in kilometres

• ‘beamtop_height [km]’ : beam top heights in kilometres

basedict

Dictionary with base polar coordinates (always in radians/metres):

• ‘azim [rad]’ : azimuth angles in radians

• ‘elev [rad]’ : elevation angles in radians

• ‘range [m]’ : range values in metres

Notes

1. The rectangular grid is returned in kilometres to match convention.