|I have now evaluated the revised manuscript ““In-situ estimation of soil hydraulic and hydrodispersive properties by inversion of electromagnetic induction measurements and soil hydrological modelling”. The authors have made extensive revisions based on the reviewer comments, and this has improved the clarity of the manuscript substantially. It is now clear what has been done and why, although I am not a big supporter of some of the (perhaps necessary) decisions that the authors have taken (see general comments below). However, this should not stand in the way of a publication of these results and insights. I have provided specific comments below that I would like to see addressed in a revised version. After these minor to moderate revisions have been adequately addressed, I recommend accepting this manuscript for publication.|
The authors prefer to use uncalibrated EMI measurements to realize an approach that does not rely on additional measurements. I am quite skeptical about this, and I would strongly prefer the use of calibration to improve the ECa measurement before inversion. It is well established that different coil configurations and orientations may require different corrections. In this same context, I see the fit to the measured data shown in Figure 3. I do not agree with the authors that this is a fairly good fit. This would perhaps be clearer if plotted as a 1:1 line. For me, the solution presented in Figure 4 is a strongly smoothed fit to the data, and the derived water content profile can only be a rough approximation of the actual water content profile. However, I agree to disagree on this issue. I do not think that this a nice approach, and I would not like to invert measurements that I know are biased. However, the results presented in this manuscript show what can be achieved when doing this. It can be left to the reader to judge for themselves whether they find this useful.
The proposed approach optimizes the hydraulic parameters layer by layer. I do not think that this is a generally valid strategy, because the water content development in one layer is not independent of the hydraulic properties of the other layers when long-time evolution is considered. However, in the case of a single infiltration event as used here I think it should be possible to do invert the parameters sequentially. I think it would be good to emphasize this in the manuscript.
Line 20. Check that all abbreviations are defined at first use. This also applies to the abstract (PTF, TDR).
Line 29. The order of the presented information is awkward here. Should the statements on the water content profile not come before the statements about the derived hydraulic parameters?
Line 82-84. Improve statement. ERT has not been used to investigate solute transport in models – it has been used in the field.
Line 88. Would be good to introduce limitations of ERT here before switching to EMI.
Line 117. Not so useful to point forward in the text here. Consider deleting.
Line 121. Avoid colloquial writing. Use “does not” instead of “doesn’t”.
Line 161. Check sentence. Two altitudes?
Line 234. Please report which model was used to relate water content and dielectric permittivity.
Line 247. Is this the thickness of the layers, or the position of the layer boundaries. Please check carefully.
Line 256. I think parameter update would be a more appropriate terminology here.
Line 310. Information about the assumed pore water electrical conductivity is missing here.
Line 363. It is well known that all channels are shifted differently. Therefore, this statement is rather optimistic.
Line 373. Be careful how you argue here, because later the hydraulic parameters derived from TDR are used as a reference to evaluate the EMI inversion results. If the TDR measurements reflect local heterogeneity and not the bulk behavior, the estimated hydraulic parameters cannot be trusted either.
Line 394. I would not mix arguments pertaining to apparent and bulk conductivity. I think that apparent bulk conductivity values need to be corrected before inversion, and this is exactly the point of von Hebel et al. (2014).
Line 441. Please carefully check the references. I found several papers that were cited in the main text, but not included in the references.
Line 451. Not sure that I understand the point that you are trying to make here. Can you improve your argumentation?
Line 480. Please also comment on the higher Ks value for the Bw horizon. It is a bit surprising given the lower fitted n-value. Any other supporting information to confirm the plausibility of the estimated parameters obtained with inverse modelling?
Figure 8. I suggest to limit the x-axis to the range of pressure head values measured in the field. This provides a more realistic impression of the fitted results. All information for more negative pressure heads is just related to fixed parameters…
Line 547. I would suggest to use the same procedure for TDR and EMI. Why should an estimate through Z be preferred over the use of the estimated TDR bulk conductivity? This just makes the results less transparent. If you keep this approach, please provide a reference to the used approach to estimate Cl- concentration from impedance directly.
Line 579. It would be nice to produce a plot such as Figure 10 using the simulated water content and solute concentration with the optimized parameters. This could show whether the high inverted concentration near the surface is well reproduced by the model. This would be important given that this region was not captured by the TDR sensors and the EMI layers at 20 and 40 cm depth. For consistency, this should then perhaps also be presented for Figure 4.
Line 628. There is evidence that the required corrections for ECa are relatively stable across different sites and conditions – this would remove the need for additional measurements.