HEADAS help file

NAME

aberattitude - Correct an attitude file for aberration effects

USAGE

aberattitude infile outfile

DESCRIPTION

'aberattitude' is a mission-independent tool, which modifies an attitude file to correct for aberration effects. The task requires an attitude input file (parameter 'infile') and computes the correction for each unique time present in this input file. The output file, specified by the parameter 'outfile' contains the corrected attitude columns along the original ones renamed with the string '_OLD' appended. For example, for an input file with a 'QPARAM' attitude column, the output file has a column named 'QPARAM_OLD' containing the original values and a column named 'QPARAM' containing the corrected values.

The aberration of light (also referred to as stellar aberration) is a phenomenon which produces an apparent motion of celestial objects about their locations dependent on the velocity of the observer.

If the parameter 'debug' is set to 'yes', the following quantities are printed for each row of the input table: 'TIME', mission time; 'VTOT', total spacecraft velocity; 'VSATX', 'VSATY', and 'VSATZ', X, Y and Z components of the total satellite velocity; 'VEARTH', Earth velocity; 'VEARTHX', 'VEARTHY', and 'VEARTHZ', X, Y and Z components of the Earth velocity; 'ERADVEL', projection of Earth velocity onto unit vector toward the observed target. The (X, Y, Z) system is a right-handed Equatorial system where X points toward the Vernal Equinox and Z toward the North Celestial Pole. Velocity unit is km/s.

PARAMETERS

infile [filename]

Name of the input attitude file.

outfile [filename]

Name of the output attitude file.

(orbfile = NONE) [filename]

Name of the orbit file used to retrieve spacecraft velocity in Earth-Centered Inertial (ECI) Cartesian coordinates. This file is required only if 'orbaber=yes'.

(alignfile = NONE) [filename]

Name of the spacecraft alignment calibration file. The alignment file specifies the rotation between the telescope and spacecraft axes.

(annaber = yes) [string]

'annaber' allows to correct for annual aberration. The allowed setting are yes, no or invert. If set to no, the default, no correction is applied. If set to yes, the effects of annual aberration are taken into account when calculating the SKY coordinate values. If set to invert, multiplies the annual aberration correction by -1 before applying it. The 'invert' option is only used for debugging. Annual aberration is the apparent bending of light due to the Earth's orbit around the Sun. This is at most a ~20.49 arcsec effect.

(orbaber = no) [string]

'orbaber' allows to correct for orbital aberration. The allowed setting are yes, no or invert. If set to no, the default, the orbital aberration is not corrected. If set to yes, the effects of orbital aberration are taken into account when calculating the SKY coordinates, provided an input orbit file is specified using the parameter 'orbfile'. If set to 'invert', multiplies the orbital aberration correction by -1 before applying it. The 'invert' option is only used for debugging. Orbital aberration is the apparent bending of light due to the satellite's orbit around the Earth. For a satellite in low-earth orbit this is at most a ~5 arcsec effect.

(attext = ATTITUDE) [string]

Name of the FITS binary table extension of the input attitude file containing the attitude to be corrected.

The attitude in the input file can be in one of three following formats specified by the parameter 'attform' (see below).

1. attform=QUAT: Quaternion [x, y, z, real]
2. attform=EULER: Z-Y-Z Euler angles (phi, theta, psi) in degrees.
3. attform=POINTING: Pointing angles (right ascension, declination, roll) in degrees.

If the attitude file contains separate columns giving the attitude in more than one format, only the column formatted as specified with the 'attform' parameter is corrected.

(attcol = QPARAM) [string]

Name of the column in the input attitude file containing the attitude to be corrected. The data in this column must be in the format given by the 'attform' parameter.

(attform = QUAT) [string]

Format of the attitude table. Three formats are supported. The QUAT format is a quaternion [x, y, z, real]. The EULER format is a Z-Y-Z Euler angle trio [phi, theta, psi] in degrees and the POINTING format.

(orbext = ORBIT) [string]

Name of the FITS binary table extension of the orbit file containing the velocity vectors.

(orbcol = VELOCITY) [string]

Name(s) of the FITS column(s) containing orbit values in the orbext extension of the orbit file. This parameter is linked to the parameter 'orbform'. The only acceptable values for 'orbcol' are: VELOCITY, VECTOR or COMPONENTS. The default is 'VELOCITY'. If 'orbform=VECTOR', then 'orbcol' is the name of the single FITS column containing the orbit values as a vector. If 'orbform=COMPONENTS', then 'orbcol' must be a string containing three comma-separated column names, specifying in order the X, Y and Z components of the orbital velocity. These columns must be scalar. Velocity must be in km/s in an Earth-Centered Inertial system.

(orbform = VECTOR) [string]

Format of the orbital velocity column or columns in the orbit file. Three formats are supported. For the VECTOR format (DEFAULT), the velocity is provided as a vector column with three elements (X, Y and Z in Earth-Centered Inertial (ECI) system). For the COMPONENT format, the velocity is provided in three separate columns.

(buffer = -1) [integer]

Rows to buffer (-1=auto, 0=none, >0=numrows).

(clobber = no) [boolean]

Overwrites the existing output file if set to yes (yes/[no]).

(chatter = 1) [integer]

Chatter level for output. Set to 0 to suppress output, or to 1, 2, or 3 for increasing the chatter of the output.

(logfile = !DEFAULT) [string]

Log filename. If set to DEFAULT uses the name of the task and, if preceded by '!', overwrite the file if it exists. If set to NONE no log file is created.

(debug = no) [boolean]

Diagnostic output is printed out on the screen if set to yes (yes/[no]).

(history = yes) [boolean]

Records tool parameters in HISTORY ([yes]/no).

(mode = ql) [string ql|hl|q]

Mode to query the parameter file. Acceptable values include: "ql (query and learn/remember), "hl" (hidden and learn/remember), "q" (query but don't remember), "h" (hidden).

EXAMPLES

1. Modify an attitude file containing the attitude in the quaternion format, correcting only for the annual aberration.

      aberattitude infile="attitude.att" outfile="attitude-corr.att" 
      alignfile="align.fits" annaber=yes clobber=yes

2. Modify an attitude file containing the attitude in the Euler angle format, correcting for the annual and orbital aberration.

      aberattitude infile="attitude.att" outfile="attitude-corr.att" 
      alignfile="align.fits" annaber=yes orbaber=yes attform=EULER 
      attcol="EULER" 
      orbfile="orbit.fits" orbext="SAT_ORBIT" 
      orbcol="SAT_VELOCITY" orbform=VECTOR clobber=yes

LAST MODIFIED