Satellite Tracking

When the radiometer system is equipped with an azimuth positioner, so that full sky scanning is possible, the instrument can run in satellite tracking mode by setting the scan mode to Satellite Tracking. 
In satellite tracking mode, the radiometer periodically scans a number of visible GPS or Galileo satellites and measures the wet delay component, LWP and attenuation in the line of sight to each of the satellites. The user should activate these products (IWV, LWP, Attenuation) in the MDF product list with identical integration time (typically one second).  The system determines the satellite positions from a RINEX navigation file stored in the TRACKING subdirectory (see section 5.1.2 of operating manual) and its own GPS position if the Navigation Info Source is set to Navigation File. The azimuth positioner’s 0.0° azimuth angle has to point to North direction (90° = East, 180° = South, 270° = West) to guarantee correct scanning positions. In the Satellite Tracking Details menu, the user can specify the tracking details.
The period determines, in which time intervals the scan shall be repeated. In ‘Scan Objects’ one can specify, if all visible satellites shall be scanned or just a single satellite. In the later case, the user must enter the satellites number. The angular scan range should be limited (e.g. in elevation) if not all sky directions are available due to obstacles.
RINEX navigation files can be loaded from the European IGS FTP data server ftp://igs.ensg.ign.fr/pub/igs/data/ and usually have the extension ‘.YYn’ where YY stands for the year, e.g. ‘.08n’ is a navigation file from 2008. E.g. the file ftp://igs.ensg.ign.fr/pub/igs/data/2008/225/dlft2250.08n is from Delft (dlft), day of the year 225  (12. August). The RINEX navigation files are ASCII formatted files and contain the orbit information for all satellites of a certain navigation system like GPS or Galileo. The host software periodically (every hour) checks if there is an updated RINEX file in the TRACKING subdirectory and automatically loads it if available. The software calculates the current positions from the information given in the RINEX files and the actual UTC time and the radiometer position on earth. 
The other Navigation Info Source option is the GPS Clock GSV source. When selected, the vectors to visible satellites are not derived from a RINEX file but from the GPS clock instead. Only GPS satellites can be scanned with this method.
Tracking data files are stored in ASCII format with extension ‘*.TRK’.