Q.] Can the "ion corr" (field#9) value in the SATXYZ log be used to correct the L1 pseudorange? What about the L2 (semi-codeless) pseudorange?
A.] The ionospheric correction in the SATXYZ log is a record of what the OEMV GPS receiver filter has applied to the L1 pseudorange. To compute an equivalent value for L2, the correction should be multiplied by (1575.42/1227.6)^2.
Q.] Where does this "ion corr" (field#9) value in the SATXYZ log come from?
A.] The correction can have been calculated from the Klobuchar model, L1-L2 measurements or the SBAS grid depending on what's available, the setting of the SETIONOTYPE command (FW 3.210 and later), and the firmware version. In FW 3.210 and later, the Extended Solution Status (field#20) in the BESTPOS log will indicate what kind of ionospheric correction is being used. L1-only models will calculate corrections based on Klobuchar model/WAAS corrections. For dual frequency L1L2 models, if enough L2 measurements are available then ionosphere correction will be calculated as L1L2 model (a real-time measurement of the ionospheric correction using scintillation differences between L1 and L2 RF propagation delay). Otherwise Klobuchar model/WAAS will be used, or the SETIONOTYPE command can be used to manually specify the ionosphere correction source.