Optimizing Semi-Airborne Electromagnetic Survey Design for Mineral Exploration
Round 1
Reviewer 1 Report
The paper describes experimental design for an important and timely mining problem, namely semi-airborne electromagnetic detection of mineralized zones. However, I do not think the work is sufficiently well-developed to warrant its publication at this time. Recognizing the long run times needed to achieve inversion results, what the authors have done is commendable. However, the results do not justify the conclusions in my opinion as the methodology is neither systematic not quantitative enough. The conclusions are essentially heuristic rules of thumb for practitioners to lay out a survey design; and the developed rules of thumb are not really surprising, so its difficult to imagine what the practitioner is supposed to take away from the paper that was not previously suspected or known. More importantly however, the analysis is too qualitative in the sense that the readar is told that a given target can be easily detected, or not detected, based on a visual inspection that is strongly biased by the arbitrary color scale that is used. A more quantitative metric, based e.g. on dB-loss or %-difference, should be developed. Also, the rules of thumb are restricted to one or two specific and highly idealized models of a mining target. While all scenarios cannot possibly be studied, I would like to see the authors make an attempt to generalize the findings. Non-dimensionalizing in terms of skin depth and resistivity contrast would be a great start in this direction. Then, general rules of thumb could be described, even if they cannot be fully implemented due to long run times. My overall recommendation is that the work is a good start but not yet ready for publication.
Author Response
Dear Reviewer
We appreciate your elaborate comments with helped to improve our manuscript. We have considered all your comments and suggestions and adapted our manuscript accordingly. We submit a revised version of the manuscript for further consideration in the journal. Changes in the revised version of the manuscript are highlighted in Blue for reviewer 1, Yellow for reviewer 2 and Green for reviewer 3. we also provide a point-by-point response explaining how we have addressed each of the reviewer comments as separate Word file.
Yours sincerely, the authors
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of “Optimizing semi-airborne electromagnetic survey design for mineral exploration” by Nazari, Rochlitz and Günther.
In this work, the authors outline a study of the optimal way to collect semi-airborne EM survey data to detect mineral deposits. Such deposits are indicated by changes in conductivity. Through a series of simulations using publicly available software (both the forward solver and the inversion code are from public repositories), the authors provide a list of suggested flight line spacing, data collection spacing along that line, as well as suggestions for the length and positioning of the transmitter cable that is placed along the ground. There are also some points about the usefulness of obtaining all 3 cartesian parameters of the H-field with the receiver.
Overall, this paper is well written and clear. The output – a set of suggestions on how to lay out a semi-airborne EM survey – is useful to a group who is going to perform one of these surveys. Given the nature of inverse problems (non-linear, and many different targets that can lead to the same measured fields, and experimental field conditions that are unique to each site), this type of ‘simulate several scenarios and then provide a set of general suggestions’ is really the only way to provide these suggestions on how to best conduct such a semi-airborne survey. Overall, I recommend the paper be published, and my comments are mostly minor:
- The motivation for the paper is not clearly explained in the introduction. The intro is just a literature review. Need to show that your study is missing in the literature.
- I highly suggest you give a description of semi-airborne EM in the introduction (i.e. before the literature review). Many readers won’t be as familiar as the authors are with the basics. To be honest, the whole introduction reads more of a ‘I want to make sure I reference every possible reviewer so I don't anger them’ than an introduction to the problem being solved and a review of the relevant literature. The introduction lanches straight into highly technical discussions. I suggest you change it or you will lose readers (and eventual references).
- The paper would be greatly enhanced if there was any experimental data available (although this reviewer does not know if an available data set exists and understands it may not be possible to get one). If there is such data available, I highly suggest you add it. It’s too easy to play games with synthetic data.
- Acronym CSEM is used without being defined.
- Definition of ‘transmitter moment’ is not given.
- What computer did you use for table 1? This matters for the run times (e.g. if this is a desktop personal computer, perhaps 19 hours could be greatly reduced by using a larger rack-based server, and then a 100x100 grid would be fine).
Author Response
Dear Reviewer
We appreciate your elaborate comments with helped to improve our manuscript. We have considered all your comments and suggestions and adapted our manuscript accordingly. We submit a revised version of the manuscript for further consideration in the journal. Changes in the revised version of the manuscript are highlighted in Blue for reviewer 1, Yellow for reviewer 2 and Green for reviewer 3. we also provide a point-by-point response explaining how we have addressed each of the reviewer comments as separate Word file.
Yours sincerely, the authors
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper investigates the effects of transmitter-receiver geometries for a variety of anomalies and semi-airborne layouts based on forward modeling and inversion. A survey layout scheme is designed based on the research results.
- The multi-component inversion results are compared and analyzed for different models and observation systems. Therefore, a brief description of how multi-inversion is implemented needs to be added.
- For the case where the anomalies under the transmitter, the data around the transmitter up to a distance of 400m from each side are removed. I would like to know the reason for choosing the range of 400m.
- When laid down the grounded-wire perpendicular to the anomalies body, the inversion results of the y-z plane are shown in this paper, but I think the inversion results of the x-z plane can be compared in this case.
- The sketch of the 3D model and the detection form of the SAEM method need further improvement (Fig. 1). There is an altitude difference between the ground-based transmitters and receivers, but in Figure 1 it looks as if they are at the same altitude.
- Some specific comments
Page 4, line 152: Unit mismatch. “The resistivity of the block and background are 1 and 300 m”. The unit of resistivity is ohm-m.
P4, 165: “Figure 1 displays a sketch of this model..”. There’s an extra “.”.
P6, 223: The reference to the Figure is mismarked. “the signal is weaker in…model (Figure A1)”. Should be changed to “Figure 4a”.
P10, 301: The reference to the Figure is mismarked. “it is better…at the same end (Figure A2 in the Appendix)”. Should be changed to “Figure A3”.
P13, 413: “…signal to-noise ratios compared to…”. Should be changed to “signal-to-noise”.
No further comments in this regard.
Author Response
Dear Reviewer
We appreciate your elaborate comments with helped to improve our manuscript. We have considered all your comments and suggestions and adapted our manuscript accordingly. We submit a revised version of the manuscript for further consideration in the journal. Changes in the revised version of the manuscript are highlighted in Blue for reviewer 1, Yellow for reviewer 2 and Green for reviewer 3. we also provide a point-by-point response explaining how we have addressed each of the reviewer comments as separate Word file.
Yours sincerely, the authors
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Paper has been revised to my satisfaction.
Reviewer 3 Report
The authors have addressed my concerns. I have no further comments this time.
