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Operation
2.7.3
Bias in TEC Measurements
NovAtel recommends calibrating the TEC to remove biases from TEC measurements. Sources of
TEC measurement bias include the GNSS antenna, antenna cable, amplifiers, splitters, connectors,
working temperature and equipment aging.
TEC measurement bias must be determined during the time of day when the Ionosphere shows the
lowest amount of activity. This varies between regions.
To improve the precision of absolute TEC measurements, follow the procedure outlined in the
sections below.
2.7.4
Determine Time of Day for Calibration
1.
Collect GPS data using the ISMREDOBS and ISMREDTEC logs. It is recommended collecting
data for a period of 3 to 4 days to even out regional effects.
2.
Identify an optimal time window to run a calibration when absolute TEC shows minimum (i.e.,
the time of day when TEC is at its minimum).
Avoid periods of significant ionospheric scintillations (sun spots).
3.
Apply satellite biases for available signal combinations (currently GPS C1P1).
Example:
SETDIFFCODEBIASES gps_c1p1 -0.207 -0.043 -0.623 1.018 ... ... 0.0 (40 values in nanosecond)
Refer to "SETDIFFCODEBIASES Sets satellite differential code biases" on page 56 for details
on this command.
2.7.5
Use GPStation-6 Auto Calibration Feature
1.
Send the following commands and logs to start the automatic calibration
•
ISMCALIBRATE Enable 0 21600 65 (0 sec to delay calibration start, 21600 calibration
duration, 65 elevation angle cutoff)
GPStation-6 User Manual Rev 2
Figure 5: TEC Before and After Example
26
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