In communications, channel models are useful approximations to the performance of a real channel, which most of the times is not available for repeated tests. In this work we present the problem over the real NVIS ionospheric scenario channel sounding, evaluating the channel propagation characteristics in terms of frequency spread and time spread, with the final goal to design a channel model. A NVIS channel model can be obtained from the evaluated channel parameters, but on one hand, there is the problem of missing data due to bad channel performance in some frequencies, and on the other hand, the measured parameters have strong dependencies between them that cannot be evinced directly. In this work, we conduct a first set of analysis to the soundings to determine the dependencies in terms of quality of the channel propagation but referring mainly to the Doppler spread and the time spread in the sensor. This classification approach will allow us to face the second part of the research, with the focus on the design of the channel model for the ionospheric communication of remote sensors.