Influence of Non-vertical Echoes to Ionogram Scaling

Digisonde DPS 4, which replaced the older ionosonde IPS 42 KEL Aerospace, started regular ionospheric soundings in the Observatory Pruhonice in January 2004. The Digisonde DPS 4 records not only ionograms, but it measures also other properties of the electromagnetic signals reflected from ionosphere (time of flight, wave polarization, amplitude, phase, angle of arrival etc.), and it provides automatic scaling of ionograms and other characteristics of the ionosphere. Additional information about the wave polarization enables us to determine and to distinguish exactly between ordinary and extraordinary wave traces on the ionogram records. This new ability basically changes scaling of the ionograms comparing to the ionograms obtained by classical ionosondes that do not provide any information about arriving wave polarization. Digisonde measurements show that in some cases the interpretation of ionograms based on classical ionospheric soundings may lead to the systematic errors, which affect classical ionograms interpretation. Here we have collected the representative data set in order to demonstrate possible differences in scaling when some complicated ionospheric situations occur. We demonstrate possible significant misinterpretations of the ionograms obtained using the classical equipment that is not able to distinguish between ordinary and extraordinary modes and records only time of flight of the electromagnetic sounding pulse. The aim of the contribution is to present comparison of the data sets measured by conventional ionosondes and by new digisondes. Errors in scaling parameters could reach several tens of MHz in frequency and several tens of km in height. We show here the necessity to be careful in using an old ionosonde measurements and scaled data for further analysis.