Ionosphere TEC (Total Electron Content) Corrections
Posted by Jose Salcido, Last modified by Jose Salcido on 01 August 2017 10:05 PM
It is now possible to apply TEC (Total Electron Content) corrections within CASA. Note that the following procedure currently only corrects for Faraday rotations, and no corrections will be applied to dispersive delays as is possible with the AIPS TECOR task.
For instructions on applying TEC corrections, please see the CASA P-Band guide found at https://casaguides.nrao.edu/index.php/VLA_Radio_galaxy_3C_129:_P-band_continuum_tutorial-CASA4.7.0#Ionospheric_TEC_Corrections
It is known that certain distributions of the Linux OS (i.e. Scientific Linux) have had issues in generating a TEC map. A few reasons for this are:
1. Linux is not able to uncompress the downloaded file with the provided command within tec_maps.py
2. Linux is missing the curl tool, which is used to download online content.
Manually download the IONEX file from NASA's Crustal Dynamic Data Information System (CDDIS) webpage, which can be found at https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/atmospheric_products.html#iono
You can search for the IONEX file via their ftp server ftp://cddis.gsfc.nasa.gov/gnss/products/ionex/
Search by YYYY/DDD/igsgDDD#.YYi.Z where,
YYYY = Year
DDD= 3-digit day
#= file sequence number for the day. 0: file contains all existing data of the current day
e.g. For an observation conducted on 2014/01/04, the IONEX file is /2014/004/igsg0040.14i.Z
Uncompress the file with the command "gzip -d <filename>", and place the unzipped file in your current working directory. Following the instructions in the CASA P-Band guide should now produce a TEC map successfully.