Comment on "Measurement of Ionospheric TEC in Spaceborne SAR Data"
Two novel approaches for measuring the ionospheric total electron content (TEC) from single-polarized spaceborne SAR data were proposed in the mentioned paper, i.e., the TEC autofocus method and the systematic alternate up/down pulse methodology. The up/down pulse methodology indicates that ionospheric TEC could be estimated using the difference between range-compressed phase distributions of the up and down chirps. However, it can be shown theoretically that the difference between the up and down chirps after compression is not expected. Thus, the estimation of TEC from alternating up versus down chirp combinations might not be feasible.