============================= ionodef.txt ===================================
This file defines the columns of data in the iono.log files produced by the
GRID software receiver. Each iono.log file contains time-stamped ionospheric
measurements. See channeldef.txt for a definition of ORT. ORT time stamps
indicate approximately the time at which the measurements apply.
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Column        Quantity

1 ----------- ORT week number. 

2 ----------- ORT whole seconds of week.

3 ----------- ORT fractional second. 

4 ----------- Pseudorange-derived slant total electron content (STEC) along
              the path from the receiver to the transmitter, in TEC units
              (TECU).

5 ----------- Change in phase-derived STEC since the previous measurement, in
              TEC units (TECU).              

6 ----------- Transmitter identification number (TXID).

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