TEC operation¶
The TEC operation produces TEC corruptions that emulate the first-order phase delays due to time- and direction-dependent ionospheric effects. A number of methods for generating the corruptions are available:
Available methods¶
- Turbulence¶
This method generates TEC values using a model of a turbulent ionosphere. The model adopts a Von Karman - spectrum for the turbulence and is based on the implementation of Buscher (2016) 1. The ionosphere is modeled as a single thin layer at a height given by hIon using the frozen turbulence approximation: the screen structure itself is constant in time, but moves with a velocity given by vIono. The strength of the turbulence is controlled by the Fried parameter r0 and the exponent of the power spectrum can be set using alphaIon. The homogeneous part of the ionosphere can be controlled setting maxvtec . This constant contribution will also cause some dTEC due to airmass effects, furthermore it is important for realistic Faraday rotation simulations. The homogeneuos TEC follows a daily modulation, peaking at 3 p.m. and attaining its minimum of 10% at 3 a.m..
- FITS¶
Currently not maintained! This method reads the TEC values from the FITS cube specified by fitsFilename. The FITS cube must conform to the format accepted by WSClean (see https://sourceforge.net/p/wsclean/wiki/ImageDomainGridder/#tec-correction). The LoSiTo TEC screen script can be used to generate such a FITS cube for a simple TEC screen.
- TID¶
Currently not maintained! This method generates TEC values from a traveling ionospheric disturbance (TID) wave. The wave has an altitude of 200 km, a peak-to-peak length of 200 km and travels at a speed of 500 km/hr. The amplitude of the wave can be specified with maxdtec, the maximum differential TEC parameter.
Parameters¶
The following parameters are available for this operation:
- method¶
This parameter is a string (no default) that sets the method to use to generate the TEC corruptions (see Available methods for details):
'turbulence'- generate TEC values from a turbulent ionosphere.'fits'- read TEC values from the FITS cube specified by fitsFilename .'tid'- generate TEC values from a traveling ionospheric disturbance (TID) wave.
- h5parmFilename¶
This parameter is a string (default is
corruptions.h5) that sets the filename of the input/output h5parm file.- r0¶
This parameter is a float (default is
10) that sets the diffractive scale / Fried parameter at 150MHz in km (only for method ='turbulence'.)- maxdtec¶
This parameter is a float (default is
0.5) that controls the maximum dTEC in one TEC-screen (in TECU). (method ='tid'only).- maxvtec:¶
This parameter is a float (default is
10) that sets the highest absolute TEC value in the daily modulation in TECU.- alphaIon:¶
This parameter is a float (default is
11/3) that sets the ionosphere power spectrum exponent. A slightly greater value of ~3.89 was found in LOFAR observations 2 3 (method ='turbulence'only).- angRes¶
This parameter is a float (default is
60) that sets the angular resolution of the screen in arcsec. (method ='turbulence'only).- hIon¶
This parameter is a float (default is
250e3) that sets the height of thin layer ionoshpere in m (method ='turbulence'only).- vIono¶
This parameter is a float (default is
20) that sets the velocity of the TEC screen in m/s (method ='turbulence'only), which controls the TEC variation frequency.- seed¶
This parameter is an integer (default is
0) that sets the random screen seed. Use for reproducibility (method ='turbulence'only).- stepname¶
This parameter is a string that sets the name of the step to use in the DP3 parset - use if you apply more than one TEC operation operation.
- expfolder¶
This parameter is a string (no default) that sets the filename of the folder in which the tecscreen data will be exported. Depending on system memory, this will not work for very large/highres screens (method =
'turbulence'only).- fitsFilename¶
This parameter is a string (default is
None) that sets the filename of input FITS cube with dTEC solutions (method ='fits'only).