Values of hmF2 deduced from automatically scaled ionograms

The values of hmF2 deduced by real-height analysis of automatically scaled vertical incidence Digisonde ionograms have been compared with those obtained using simple methods based on routinely scaled ionospheric characteristics. Comparisons have been made for ionograms recorded at five stations during low solar activity. The real-height analyses used Titheridge's program POLAN, while the simple methods used were those of Dudeney and Bilitza. Systematic discrepancies between the simple-model and POLAN values of hmF2 were found, with 15–20 km overestimates of hmF2 by the simple methods during the night. The majority of discrepancies lie between ±20 km. During the day, 80% of discrepancies lie between ±10 km. Significantly larger discrepancies can usually be attributed to special ionospheric conditions or ionograms, failure of the automatic scaling technique, or failure of one of the basic assumptions of the simple models.