Airborne Electromagnetic, Magnetic, and Radiometric Surveys at the German North Sea Coast Applied to Groundwater and Soil Investigations
Round 1
Reviewer 1 Report
Thank you for considering me as a reviewer of Remote Sensing manuscript remotesensing-804019 by Bernhard Siemon, Malte Ibs-von Seht, Annika Steuer, Nico Deus, and Helga Wiederhold, titled ‘Airborne electromagnetic, magnetic and radiometric surveys at the German North Sea coast applied to groundwater and soil investigations’. My recommendation is that this article should be accepted for publication after minor revisions. It would not have to be sent back to me; and the Associate Editor could judge if the corrections are satisfactory.
The manuscript ‘Airborne electromagnetic, magnetic and radiometric surveys at the German North Sea coast applied to groundwater and soil investigations’ summarises and explores the results from extensive airborne geophysical surveys conducted over the North Sea coast of Northern Germany over more than 15 years. The authors show how the regional geophysical surveys provided new knowledge and confirmed theories about hydrological processes, hydro geophysics, and landscape changes on this important coastline. My immediate question here, which is not entirely relevant to the paper, is an estimate of the total cost for the surveys, research, and subsequent design and analysis of the surveys. I wonder about this for interests’ sake, and quietly question myself on how much would it cost to get the same level of understanding from drilling alone?
I have found this manuscript to be a pleasure to read. It is well-structured, informative, and easy to follow for one who knows very little about the landscape evolution of Northern Germany. I specialise particularly in airborne electromagnetics; but found the sections on magnetics and radiometrics to be also interesting and clear. I have no criticism of the paper, since it is the result of more than a decade of work. It is structurally sound and clear. The expositions on airborne geophysical methods and the different aircraft platforms are complete and extensive without being boring.
I found it particularly interesting how information was gained about soil structure, saltwater intrusion and freshwater discharge by using a fusion of the different geophysical techniques. It is clearly a mostly sedimentary environment, based on the magnetics, but the AEM shows interesting features that, when combined with radiometric analysis and auxiliary borehole information, provide clear examples of the powerful interpretation that can be gained by combining multiple methods. Well done on a clear and enjoyable paper.
I have found a few sentences in the manuscript to be unclear and overly complicated. Some words have been misspelled or mis-used. These are infrequent, and I have marked them in the commented document that I include with this review.
There are only a few criticisms about the quality of the figures. There are no negative indicators on the numbers of the scale for magnetic anomaly in Figure 4a. I would prefer the intensity of colour in Figure 5a to be as great as it is in 5b. The exposure rate appears to be a little under-exposed. The flight line numbers in Figures 6 are not legible at the resolution that I received for review. They may be higher resolution in the final document, but I don’t really believe they contribute much: I would consider removing the line numbers but retaining the flight lines. I found Figure 7 particularly vexing. I can’t see the lines indicated in the text. Even using the legend is rather difficult. I would like to see the lines formatted differently, with colours that contrast better than the red-on-red that are presently there. The lines for Geest and bog in Figure 12 are too similar. My final comment is that there are no graticules or tick marks on any of the figures indicating spatial location. I see the scale bar, but there is no reference to any projections or locations. Finally, there is no regional/local map indicating where Northern Germany is in Europe or its proximity to Scandinavia. I realise that to find space to include an inset on Figure 1 is limited, but I consider contextual location to be of importance.
Again, thank you very much for the opportunity to review this interesting article. I look forward to seeing it published.
Comments for author File: 
Comments.pdf
Author Response
Please find our response in the file attached: author-coverletter-7250621.v1.pdf.
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript “Airborne electromagnetic, magnetic and radiometric surveys at the German North Sea coast applied to groundwater and soil investigations” presents the results of a large, intensive geophysical survey of an area with many groundwater challenges. Multiple surveys from several techniques over a period of several years were stitched together to form a series of maps for the German coastal area. The discussion focuses on interpretation of the results related to groundwater salinity, freshwater lenses, peat thickness, and other aspects of the geology and hydrogeology. The study demonstrates how regional mapping using remotely sensed, airborne geophysical surveys can be combined to increase understanding of hydrogeological processes and geological features.
The paper is well written and the narrative flows nicely from one section to the next. The interpretations are supported by the data, and the authors do a fine job of explaining the advantages and limitations of the methods. Overall the manuscript is in very good shape. This is a high-quality paper worthy of publication. I have a few comments and suggestions for improvement detailed in line-by-line comments below.
The abstract could use improvement. Some mention of the results and overall conclusions should be included in the abstract. As written, the abstract simply indicates that the work was completed and the results were displayed in maps. As a reader, I want to know what was found or how it might apply to my interests. A more informative abstract will draw the reader to go beyond the abstract and it will increase readership.
Line 68: The title “Materials and Methods” is not appropriate here, as the following paragraphs describe the physical setting of the study area. Please insert this heading above line 126 at the start of the methods as a new section (Section 3). Then, promote the heading “Study area…” to a main heading (Section 2). Re-order the subsequent section numbers appropriately.
Line 72: Replace “accrued” with “deposited”.
Line 74: “Intercepted” is not the best verb choice here. A better verb might be “interrupted”.
Lines 79-80: The noun described as “north European area” can be replaced by the simpler form, “northern Europe”.
Line 91: A better verb choice for “almost describes” might be “closely follows”, “closely matches” or “is nearly coincident with”.
Line 104: The part “rises similar to the sea level” is unclear. What do you mean by this? Can you be more specific? Does it mean that the water table rises upward as the sea level increases in elevation?
Line 105: The part “subsequent frequently eroded” is unclear and uses incorrect grammar. Can the word “subsequent” be deleted while still retaining the original meaning of the sentence? If so, this would fix the problem here.
Line 108 – 109: The sentence spanning these two lines uses both past tense and present tense. Please use consistent tense.
Lines 114 – 116: This sentence contains too many ideas. It would be good to set the phrase in the middle of the sentence apart from the rest of the sentence by using em dashes. I suggest revising as follows: The coastal regions in Lower Saxony are characterized by low groundwater recharge rates in the marshland—interpreted on the basis of widespread Holocene brackish and marine cohesive sediments—and higher recharge rates in the moraine areas.
Line 118: Delete “groundwater”.
Lines 306-307: Please revise this sentence. It is a little confusing because it mixes lithological terms. You can delete the word “obviously”. Mineralogical clay is electrically conductive, not sediments in the grain-size range of clay. The segment “sand (silt, till)” should be revised as these are all different lithologies. Does the till contain clay?
Line 359: The verb “swims” is not appropriate here, as it implies animal behavior. I suggest using a different verb.
Line 423: Delete comma in 2nd sentence.
Line 506: The phrase “missing increase in surface elevation” could be better described. I suggest replacing it with “lack of storage due to low elevation and flat topography”.
Line 575: “Both is” should be changed to “both are”.
Line 699: Delete comma.
Figures: Dashed lines indicating fresh/saline interfaces (Figures 3, 7, 10, 11) are difficult to see. Can line thickness be increased in figures 7 & 10? In figure 3, I cannot distinguish between blue and red line colors. Dash pattern is the best way to distinguish the lines. In figure 11, I need to zoom to greater than 150% to see the line colors. Is it possible to make the lines stand out better?
Author Response
Lease find our response in the file attached: author-coverletter-7251118.v1.pdf.
Author Response File: Author Response.pdf
