I am a new user for gps data and I need help:
I am using the ashtech software (winprism) to transfer data from the receiver to my computer. But I can find anywhere the meaning of some terminology used. The questions are:
- What does `TXMTTIME' mean ?
'CDPHSE'
'SM_CNT'
'NAVX,Y,Z,T'...
- Where can i get some basic docs about using GPS data to study the ionosphere? thanks very much
fethi

With the WinPrism S/w program "Filetool" use the "Print Struture Format" option to print the B-File Header information.
The Terms your asking about are defined.

Basically "TXMTTIME" is time stamp record for the current measurement. Time of issue from Satellite

"CDPHSE" = Code Phase
"SM_CNT" = Smooth Count
"NAVX,Y,Z,T" = navigation velocity info.

Bob LeMoine
Ashtech Precision Products

More detailed information on the Ashtech raw measurement data structures can be obtained from the "Z Family" technical manual, which is available in PDF form on the anonymous ftp server accessed via the Ashtech website. This manual can be found in the firmware\zsurvey folder. The filename is family.pdf, 2.5 Mbytes in size.

To develop Bob's comments a bit further, the TXMTTIME is the time of transmission of the code that was received at the RECEIVE TIME. The receive time is the actual time tag for which the measurement is valid, expressed in GPS seconds-of-the-week. The difference between the transmit time and the receive time multiplied by speed of light is the raw pseudorange measurement in meters, called "CDPHASE" in the Ashtech B-file. SM_CNT (smooth count) is a measure of how long the receiver has maintained lock on a particular satellite. NAVX, NAVY, NAVZ and NAVT are the computed raw ECEF X, Y and Z coordinates and the receiver clock offset, respectively. The velocities in the X, Y and Z directions are labeled NAVXDOT, NAVYDOT and NAVZDOT.