attitude_analysis: Module to obtain instrument pointing direction in various reference frames

attitude_analysis module includes functions for finding the instrument pointing direction in spacecraft orbital frame(ORF), GEI J2000, ECEF, ITRF,

NEC, NED and ENU.

Additional functions are available to calculate the look angles of the spacecraft and the instrument with respect to a ground point, line-of-sight look direction vector from the ground point to the spacecraft and the distance between spacecraft and the ground point. Slew quality can be calculated given the threshold for the angle between the LOS direction and the instrument pointing.

@author: ceren

attitude_analysis.LA_inst(vec, e, n, lon, lat, pLon)

vecArray of float: Boresight pointing vector.
eint: Column of the east vector in vec.
nint: Column of the north vector in vec.
lonnumpy.ndarray[float]: spacecraft longitude (degrees).
latnumpy.ndarray[float]: spacecraft latitude (degrees).
pLonfloat: Longitude of the target on the ground (degrees).

dictdict

Look angles of the instrument: azimuth and depression. vec_azim: Array of float

Look angle of the instrument in horizontal plane (degrees)

vec_dep: Array of float: Depression angle of the instrument (degrees)

inst_look_angles = LA_rri(RRI_enu, 0, 1, Lon, Lat)

attitude_analysis.LA_sat(plon, plat, palt, slon, slat, salt)

Calculates the satellite look angle: elevation and azimuth angle that is needed for the satellite to look towards a point in GEO frame.

Ref: ASD5: Earth Station Look Angles By Prof. Gregory D. Durgin,: Astrodynamics, Georgia Tech, 2009.

plonfloat: Longitude of the target on the ground (degrees).
platfloat: Latitude of the target on the ground (degrees).
paltfloat: altitude of the point in GEO frame (km).
slonnumpy.ndarray[float]: spacecraft longitude (degrees).
slatnumpy.ndarray[float]: spacecraft latitude (degrees).
saltnumpy.ndarray[float]: altitude of satellite in GEO frame (km).

dictdict

Look angles of the spacecraft: azimuth and elevation. azimuth: numpy.ndarray[float]

Satellite location in terms of azimuth (degrees).

elevation: numpy.ndarray[float]: Elevation angle of the spacecraft (degrees).

sat_look_angles = LA_sat(plon, plat, palt, slon, slat, salt)

attitude_analysis.calculate_los_vec(pLon, pLat, pAlt, slon, slat, salt)

calculates line-of-sight vector from a point to the spacecraft location using the geopy.dist.geodesic

plonfloat: Longitude of the target on the ground (degrees).
platfloat: Latitude of the target on the ground (degrees).
paltfloat: altitude of the point in GEO frame (km).
slonnumpy.ndarray[float]: spacecraft longitude (degrees).
slatnumpy.ndarray[float]: spacecraft latitude (degrees).
saltnumpy.ndarray[float]: altitude of satellite in GEO frame (km).

los_enu_arrnumpy.ndarray[float]: line-of-sight vector from the point to the spacecraft in ENU system.
los_ned_arrnumpy.ndarray[float]: line-of-sight vector from the point to the spacecraft in NED system.

attitude_analysis.calculate_reception_angle(inst_ned, pLat, pLon, pAlt, lat, lon, alt, inst='boresight')

function to calculate the reception angle of an instrument. reception angle: angle between the instrument look direction vector and the line-of-sight vector from the target

inst_nednumpy.ndarray[float]: instrument look direction vector in North-East-Down.
pLatfloat: geodetic latitude of the target (degrees).
pLonfloat: geodetic longitude of the target (degrees).
pAltfloat: Altitude of the target (km).
latnumpy.ndarray[float]: spacecraft position in geodetic latitude (degrees).
lonnumpy.ndarray[float]: spacecraft position in geodetic latitude(degrees).
altnumpy.ndarray[float]: spacecraft altitude (km).
inststr, optional: cra is calculated as (90-ra) for dipoles, (180-ra) for boresight. input can be boresight or dipole. The default is ‘boresight’.

ra_losnumpy.ndarray(float): reception angle of the instrument (degrees).
cra_losnumpy.ndarray(float): complementary reception angle of the instrument (degrees).

attitude_analysis.find_instrument_attitude(rotated_body, geiX, geiY, geiZ, geiVx, geiVy, geiVz, geoX, geoY, geoZ, time_array, start_date, end_date, lat, lon, path_to_sofa_files, method1='ephemeris', frame2='itrf', frame3='nec')

Takes in the rotated body vector in orbital frame and outputs instrument look direction in NEC or NED coordinate systems by utilizing the functions in use_rotation_matrices module.

rotated_bodyTYPE: DESCRIPTION.
geiXnumpy.ndarray[float]: X position in GEIJ2K (km).
geiYnumpy.ndarray[float]: Y position in GEIJ2K (km).
geiZnumpy.ndarray[float]: Z position in GEIJ2K (km).
geiVxnumpy.ndarray[float]: X component of velocity in GEIJ2K (km/s).
geiVynumpy.ndarray[float]: Y component of velocity in GEIJ2K (km/s).
geiVznumpy.ndarray[float]: Z component of velocity in GEIJ2K (km/s).
geoXnumpy.ndarray[float]: X position in GEO (km).
geoYnumpy.ndarray[float]: Y position in GEO (km).
geoZnumpy.ndarray[float]: Z position in GEO (km).
time_arraydatetime.datetime: time.
start_datedatetime.datetime: start of the experiment.
latnumpy.ndarray[float]: Geodetic latitude in degrees.
lonnumpy.ndarray[float]: Geodetic longitude in degrees.
path_to_sofa_filesstr: path_to_initialization files (IERS and EOP).
method1str, optional: Transformation method to ICRF/GEI J2K. Can be ‘ephemeris’ or ‘orbital_elements’. The default is ‘ephemeris’.
frame2str, optional: Terrestrial frame: ‘ecef’ or ‘itrf’. The default is ‘itrf’.
frame3str, optional: Final coordinate system: ‘nec’ or ‘ned’. The default is ‘nec’.

inst_geonumpy.ndarray[float]: instrument look direction in the requested coordinate system:NEC or NED

attitude_analysis.find_slew_inst(ra_los, criteria)

function to classify slew according to the given criteria: 1 : Front face slew 0: no dipoles slewed -1: Back face slew

ra_losnumpy.ndarray[float]: Boresight reception angle (degrees).
criteriafloat: criteria/threshold for slew (degrees).

slewint: Classification of slew according to the given criteria

attitude_analysis.find_slew_rri(ra_los, ra_D1, ra_D2, criteria)

function to classify slew according to the given criteria: 2: Front face slew 1: 1 dipole back, 1 dipole front, boresight front slew 0.5 : 1 dipole front slew 0: no dipoles slewed -0.5: 1 dipole back slew -1: 1 dipole back, 1 dipole front, boresight back slew -2: Back face slew

ra_losnumpy.ndarray[float]: Boresight reception angle (degrees).
ra_D1numpy.ndarray[float]: Dipole1 reception angle (degrees).
ra_D2numpy.ndarray[float]: Dipole2 reception angle (degrees).
criterianumpy.ndarray[float]: criteria/threshold for slew (degrees).

slewint: Classification of slew according to the given criteria

attitude_analysis.rotate_inst(body_vec, Roll, Pitch, Yaw)

Rotation of body vectors in orbital frame (ORF) of Swarm-E using roll, pitch, and yaw angles.

The rotation sequence is X->Y->Z; roll->pitch->yaw according to the RRI data description.

Ref: University of Calgary, e-POP Radio Receiver Instrument (RRI) User’s Manual, Doc. no. ePOP-5024, Rev. D (2018)

https://epop.phys.ucalgary.ca/data-handbook/coordinate-systems/

body_vectuple: x, y, z : initial position vectors for antenna in ORF
Rollfloat: roll angle in degrees
Pitchfloat: pitch angle in degrees
Yawfloat: yaw angle in degrees

rotated_bodynumpy.ndarray: rotated body vectors of instruments onboard Swarm-E in ORF

attitude_analysis.spacecraft_distance_from_a_point(pLon, pLat, pAlt, slon, slat, salt)

calculates spacecraft distance from a point using the geopy.dist.geodesic

plonfloat: Longitude of the target on the ground (degrees).
platfloat: Latitude of the target on the ground (degrees).
paltfloat: altitude of the point in GEO frame (km).
slonnumpy.ndarray[float]: spacecraft longitude (degrees).
slatnumpy.ndarray[float]: spacecraft latitude (degrees).
saltnumpy.ndarray[float]: altitude of satellite in GEO frame (km).

distancenp.ndarray[float]: slant range between the ground point and spacecraft (km).