|The revised manuscript has been significantly improved compared to the original manuscript and duplications within the text have been removed. However, there still remain some open points, which I suggest to by clarified before publishing. All my new comments refer to the revised manuscript with changes marked, which I got from the Copernicus editorial office (hess-2017-538-author_response-version1.pdf). After finishing my review I realised that there are differences compared to the uploaded revised version without changes marked. I don’t know if this is a sloppiness of the authors or caused by a mix up of the editorial office. |
The description of amplitude handling has been mostly clarified and an additional flow chart has been provided as suggested. Please also include amplitude handling for the event detection (amplification with arbitrary fct prop t^2, page 11, line 3) in this chart. Please also specify the normalisation in the signal preprocessing box and provide an explanation in the text: does this mean that every radar trace (A-scan) is normalised to its maximum level and these normalised data are used for inversion?
Compared to the original manuscript, spherical divergence is not corrected any more (page 10, L 3-5 has been deleted as it included an incorrect formula). However, regardless the different amplitude handling, the inversion results remain exactly the same compared to the original manuscript. Is this correct?
Effective dielectric properties:
As I understand, you deduce the conductivity from the TDR pulse shape so that it corresponds to the effective conductivity, which includes DC conductivity and dielectric losses. I suggest to make this explicitly clear in the text (e.g. P7 L17). Please also describe how conductivity has been deduced from the TDR data in one sentence (amplitude, shape, which software, references?).
Assuming constant conductivity during the experiment (P8 L23):
This is still my main concern. As the water content changes in the sediment, intrinsic attenuation will also change. Please discuss your assumption of a constant effective conductivity critically and provide an estimate of the effects that you neglect (see my comment in the first review, second main point). For instance calculate and compare attenuation for saturated and unsaturated sand and the effect on reflection amplitudes of signals stemming from deeper interfaces of the experimental setup. I’m wondering that the synthetic data can fit the field data when attenuation effects are assumed to be constant during the experiment.
Further minor comments
(P1 L5) “…signal originating from a fluctuating groundwater table…” is misleading as also reflections at internal interfaces are used.
(P3 L30) “…multi-channel common offset GPR…” you mean multi-offset GPR? The nomenclature “multi-channel” only describes the GPR apparatus but does not provide any information on the measuring layout.
(P11 L3) “preprocessed amplitude”. What does this mean, please also include this in Fig. 3.
(P13 L5) “standard deviation of the measured normalised travel time … and the measured normalized amplitudes”. To me it is not clear how the standard deviations are calculated. Is this the STD of all measured traveltimes/amplitudes for one event during the experiment including changes caused by water table fluctuations or what are the input data for the calculation?
(P16 L25) Infinite dipole: … Gauss dot wavelet leads to a Ricker wavelet. To my knowledge this is only true for 3D simulation but not for 2D simulation especially for the phase spectrum. Please check.
Fig. 9, caption: “radargram is normalized to its maximum absolute amplitude”. The whole radar section is normalised to its maximum or each trace (A-scan) is normalised independently?
(P24 L2) “…calculated the difference to the true water content distribution”. $\Delta$ = true – mean or vice versa?
Figure 13: For every time step, there are much more residuals plotted than localised events.
uncomplete sentences: (P23 L6), (P26 L10), (P26 L27), (P28 L4), (P31 L12), (P31 L26), (P31 L26), (P34 L12), (P34 L21)