the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Sep 2025
The Potsdam Soil Moisture Observatory: High-coverage reference observations at kilometer scale
Abstract. Cosmic-ray neutron sensing (CRNS) has gained popularity for estimating soil water content (SWC) due to its innovative capability to measure at an intermediate scale – a notable advantage over point-scale sensors, which are often sparsely installed and due to small-scale heterogeneity result in uncertain absolute values. CRNS serves as a crucial link between small and large scales and has been emerging as a reference measurement for remote sensing algorithm validation for its ability to link the small and large scales. Yet, the sparse availability of long-term datasets limits use of this possibility. Within the framework of project SoMMet (21GRD08), multi-scale soil moisture monitoring was implemented to integrate CRNS with complementary in-situ observations. In this paper, we present harmonized soil moisture data from different sensor types including a CRNS cluster, shallow soil moisture measurements and soil moisture profile data, creating a ready-to-use dataset as reference observation for remote sensing products, covering a highly-instrumented agricultural site in the northeast of Germany. The data include 16 stationary CRNS sensors, with co-located point-scale SWC sensors (mostly permanent), two groundwater observation wells, meteorological records, and data from intensive manual sampling campaigns (covering SWC, bulk density, organic matter, etc.). This dataset distinguishes itself from prior studies by the increased area of approx. 1 km² while still having a high sensor density and overlapping footprints of CRNS. This allows a reasonable degree of geostatistical interpolation to obtain complete coverage. The data are available under the (https://doi.org/10.23728/b2share.db88e149f7924919be376909856739f1) (Grosse et al., 2025), providing a new reference data set for remote sensing products, hydrological or land-surface models and for other products linked to soil water balance.
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Status: final response (author comments only)
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RC1: 'Comment on essd-2025-546', Anonymous Referee #1, 30 Sep 2025
- AC1: 'Reply on RC1', Peter Grosse, 20 Oct 2025
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RC2: 'Comment on essd-2025-546', Anonymous Referee #2, 09 Oct 2025
This paper presents several extensive datasets collected concurrently from an agricultural area in Germany. The availability of such a diverse range of measurements within a geographically restricted area provides unique opportunities for soil moisture data analysis, as well as for testing data correction and modelling approaches. The authors are to be commended for assembling such a high-quality dataset.
As already noted in the previous review, the manuscript contains many errors and at times gives the impression of a draft. The overall structure requires substantial revision (see specific comments below). While the tables and figures are mostly informative and provide a good overview of the data, the data archive structure and description should be improved (see specific comments below).
Specific comments
The Introduction should conclude with a concise summary of the paper’s structure and the data presented in this data paper.
L59: There are more paper on signal correction that could be mentioned here, e.g. Baatz et al., (2015) introduced a biomass correction for CRNS, Davies et al. (2022) tested optimal temporal filtering methods for CRNS.
62: Brogi et al. (2022) is not about biomass estimation using CRNS. I believe you meant Brogi et al. (2025).
L63: Here you could also cite Bogena et al. (2020).
L65-67: This sentence is unnecessary and could be removed.
L75: “three such data sets“
L123: A separate “Highlights” chapter does not appear necessary. Consider integrating its content into the Introduction as part of the motivation.
L125: This statement is difficult to understand without referring to Figure 2.
L137: Refer to Fig. 2.
L157: Methods and results are mixed in this chapter, which is inappropriate for a scientific publication. Please restructure the manuscript to clearly separate them. You may refer to Heistermann et al. (2022) as a good example, where the methods are presented first, followed by two separate chapters describing the data provided with the paper and exemplary results from the data analysis.
L182-185: Since all CRNS stations are located in close proximity, it would be more appropriate to use meteorological data from the reference station for corrections of all CRNS stations. This approach ensures that corrections are applied consistently, increasing data consistency. Moreover, reference data are generally more accurate than the lower-quality sensor data used at the CRNS stations.
L184-188: In agricultural fields, such as those in this study, biomass changes constantly over the years, which can significantly influence CRNS signals depending on the type of vegetation (e.g., Jakobi et al., 2022). Therefore, the calibration will not implicitly account for this effect. Please discuss this aspect.
L208: The chapter on Bonner sphere measurements feels somewhat isolated. It is also rather long and distracts from the main focus of the paper, i.e., soil moisture data. Therefore, this chapter should be shortened and better integrated into the manuscript.
L399: The section on stable water isotopes in soil and groundwater appears off-topic for a paper focused on soil moisture. Given that only three campaigns may not provide sufficient accuracy to infer groundwater recharge, and the paper already covers a wide range of topics, consider removing this part.
L514-521: Unfortunately, this example demonstrates that the dataset’s value for remote sensing validation is quite limited, as only a few grids of the RS product are actually covered by the CRNS data, with most sensors clustered within a single grid. Therefore, I suggest removing this part.
Data archive
I downloaded some of the data (e.g., CRNS, profile, muon) to check whether the files are well documented and complete. The README file provides a good overview of the data and the units of the values. However, there is no description of the file formats. In addition, the CRNS data are split across two separate files, which is confusing. The same issue applies to the SWC profile data.
Figures
Figure 1 only shows locations of CRNS stations (not shallow SWC and SWC profile stations)
Figure 5: The graph on the right is not easily readable and should be enlarged. The image on the left does not add much value.
References
Baatz, R., Bogena, H. R., Hendricks Franssen, H. J., Huisman, J. A., Montzka, C., & Vereecken, H. (2015). An empirical vegetation correction for soil water content quantification using cosmic ray probes. Water Resources Research, 51(4), 2030-2046.
Bogena, H. R., Herrmann, F., Jakobi, J., Brogi, C., Ilias, A., Huisman, J. A., ... & Pisinaras, V. (2020). Monitoring of snowpack dynamics with cosmic-ray neutron probes: A comparison of four conversion methods. Frontiers in water, 2, 19.
Brogi, C., Jakobi, J., Huisman, J. A., Schmidt, M., Montzka, C., Bates, J. S., ... & Bogena, H. R. (2025). Cosmic-ray neutron sensors provide scale-appropriate soil water content and vegetation observations for eddy covariance stations in agricultural ecosystems. Agricultural and Forest Meteorology, 373, 110731.
Davies, P., Baatz, R., Bogena, H. R., Quansah, E., & Amekudzi, L. K. (2022). Optimal temporal filtering of the cosmic-ray neutron signal to reduce soil moisture uncertainty. Sensors, 22(23), 9143.
Jakobi, J., Huisman, J. A., Fuchs, H., Vereecken, H., & Bogena, H. R. (2022). Potential of thermal neutrons to correct cosmic‐ray neutron soil moisture content measurements for dynamic biomass effects. Water resources research, 58(8), e2022WR031972.
Citation: https://doi.org/10.5194/essd-2025-546-RC2 -
AC3: 'Reply on RC2', Peter Grosse, 05 Nov 2025
The comment was uploaded in the form of a supplement: https://essd.copernicus.org/preprints/essd-2025-546/essd-2025-546-AC3-supplement.pdf
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AC3: 'Reply on RC2', Peter Grosse, 05 Nov 2025
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RC3: 'Comment on essd-2025-546', Anonymous Referee #3, 14 Oct 2025
This is a very comprehensive dataset and worth publication. I only have a few suggestions:
(1) The color scheme of Fig. 2 could be updated to improve the contrast among vegetation types. It is very difficult to tell them apart in the map.
(2) Fig. 4 - please note the interpolation method.
(3) A key limitation of cosmic ray neutron sensors is that their penetration depth is approximate, but this site has the advantage of multi-depth conventional soil moisture sensors. Could a comparison graph between CRNS and conventional sensor be made - perhaps similar to Fig. 3, but showing the difference between the CRNS measurements, and the conventionally measured values interpolated to the same nominal depths? This will be very useful in giving the readers an understanding of the measurement uncertainty.
Citation: https://doi.org/10.5194/essd-2025-546-RC3 -
AC4: 'Reply on RC3', Peter Grosse, 05 Nov 2025
The comment was uploaded in the form of a supplement: https://essd.copernicus.org/preprints/essd-2025-546/essd-2025-546-AC4-supplement.pdf
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AC4: 'Reply on RC3', Peter Grosse, 05 Nov 2025
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RC4: 'Comment on essd-2025-546', Wolfgang Wagner, 20 Oct 2025
This paper presents a highly valuable dataset for soil moisture research and is worth publishing after revisions to enhance its presentation. My general comments are as follows:
- The paper primarily is a comprehensive description of all data collected at the Potsdam Soil Moisture Observatory, and while reading it I felt a certain fatigue towards the end of the paper. To improve engagement of the readers, I recommend incorporating more visualizations to highlight the properties and quality of the different datasets. Additionally, including some exploratory results could make the paper more compelling.
- Section 6 discusses the validation of the Copernicus SWI product as a use case. However, while the fused ASCAT-Sentinel-1 1 km SWI product is sampled at 1 km (hence its acronym 1km SWI), its effective spatial resolution is much coarser (~5–15 km; see, e.g., [DOI: 10.1016/j.jhydrol.2022.128462]). Instead, it would be more appropriate to reference e.g. the 1 km Copernicus Sentinel-1 surface soil moisture (1km SSM) product, which not only has fine sampling but also a high resolution of 1km.
- As noted by other reviewers, the English language needs improvement, particularly in the introductory sections.
- In line with RC2’s feedback, the section on the Bonner sphere appears out of place and should be rewritten to fit better with the rest of the text.
Minor comments:
Figure 3: Why is the intense precipitation event in summer 2024 (> 30 mm/d) not visible in the CRNS time series?
Figure 3: It would be nice to see also normalized soil moisture values to better compare the time series.
Line 227: What is an “unfolding procedure”?
Line 233: Weird to read here: “The objective of this study is twofold …”
Citation: https://doi.org/10.5194/essd-2025-546-RC4 -
AC2: 'Reply on RC4', Peter Grosse, 05 Nov 2025
The comment was uploaded in the form of a supplement: https://essd.copernicus.org/preprints/essd-2025-546/essd-2025-546-AC2-supplement.pdf
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EC1: 'Comment on essd-2025-546', Jiafu Mao, 13 Nov 2025
The following are additional comments from one of the reviewers for the authors’ consideration:
General commentsThe authors present cosmic ray probe data from the "Potsdam Soil Moisture Observatory in Germany together with some results to increase interest in the data.First, the data set is very valuable and should definitely be published. Note however that I did not check the data set itself. Time and demand will show if the data can be extracted at reasonable costs.Second, it is still too obvious that the paper was written by different authors and then compiled. What is missing here is a cleansing force that defines standards and then enforces them. Regrettably, time and effort spent on the paper are not commensurate with the effort involved in collecting the data. No question that homogeneizing the paper is work, but it would pay off handsomely. I therefore appeal to the authors to make a further effort to improve the paper.Third, the entire observatory has obviously developed over the years into what it is today. The historical heterogeneity is evident. It is also addressed, but often in euphemistic language. I don't think that this is good. Scientists are not politicians, but peers to whom one can be honest. For example, it is obvious that the distribution of sensors is somehow historically conditioned, but overall it does not seem to follow a super master plan. No one would cluster the sensors in the eastern area and then place one sensor (no 39) so isolated in the landscape, as is the case here. As a scientist, I fully understand such constraints, but I don't want to be taken for a fool.Specifically, I would suggest dealing with the history in a separate section and then describing the structure as objectively as possible in the style of a Materials and Methods chapter, as is done quite convincingly later in the paper.Further sugarcoating concerns the CRNS measurement method itself. Sure, the sensors cover a larger area, but firstly, as far as I know, the depth is unclear and also depends on the measured variable itself, and secondly, the signal is further distorted by vegetation, as is very shortly described in the paper further on. I would like to see a few more candid words about the possibilities and limitations of the measurement method. This would also broaden the audience, as not every possible user is familiar with the CRNS methodology.Specific commentsline 11define (spell out) SWC19why "but"?22better"but also to applications such as"35observe data? Sounds wrong to me. Variables are observed, the data are next step, they are gathered, collected…area-representative37better "soil tillage"39I would rather call it "assessment", although the difference to measurement is gradual.This becomes obvious later in line 48 (depends heavily)75This is not well elaborated and therefore confusing: On the one hand, the authors stress that it is great that CRNS is an integrating measurement method, on the other hand they advertise the possibility to measure heterogeneity. It is clear that this is scale-dependent but this could be presented more clearly. And the authors should also not withhold that the support volume of CRNS is state-dependent, that it integrates not only the SWC, but also the water content of canopies (see General comments). It is better to address these issues frankly than to keep them to yourself.81Past and perfect tense ("was" and "has aimed") do not go together well82better "particularly high density"Around 85Better describe what it is and why it was established, not how it developed. Short and concise, and important things first would be best. The history of PoSMO follows in section 2 anyway and that's where it belongs.108Better "Crops grown include"109no hyphen necessary111Top soil? which soil depth?add "sand content" and "by mass" (If correct) between the brackets112by mass?113"average temperature" is enough, or what is the added meaning of "annual" here?114"ground surface"two … were installed in 2019" is enough. "continue to provide data" goes without saying.116better "provide"120environment121this is a meaningless sentence (Its setting enhances…), I would delete it. If not, it should be moved to the Conclusions.123It would be better to replace the section 2.2 by a discussion of the strengths and weaknesses and to move it to the end of the text, after the data and related measurement methods have been presented. Rather like a Conclusion section, e.g. under the title "Conclusion and Highlights".Figure 1 captionI do not agree at all. It is an unfounded claim that the measured SWC represent the field plots as indicated. In particular, if different crops are grown on the plots. And is there any explanation why the footprints of the CRNS are so different? And why they coincide with the agricultural plots?It is also not clear what the numbers mean. And it is unclear what the meaning of shallow SWC and SWC profile is.126The CRNS sensors were placed, not the locations128The land use is all but similar as you state yourself above. And in the following line you even mention grassland, which is a very different land use.This is the first time that "soil type" is mentioned, but no soil type is specified - your statement lacks trustworthyness. Better be more specific. You could build up trust by providing a soil map in Supporting Materials.136this is redundant150on 17 FebruarySection 2.2 as a wholeThe authors should remove the promotional tone, including the promotional headline, and instead describe precisely what was measured, when, at what frequency, at what resolution, and using what methods.The whole section is not well written. I think you should either stress the highlights or give details in Material and Methods style. The mixture is really unsatisfying. See recommendation in the General comment.Figure 2The graph is too small and the quality insufficient. The color coding is unreasonable.What do the numbers stand for?Circles should be explained.Unnoticed by the authors, the caption contradicts the statement of representativeness made in Figure 1.167first time that a hillslope is mentioned169cropped areas.The table could be much more useful if extended by quantitative information about spatial coverage and the frequency of the observations. In its present form, the information is fragmented. E.g. it is not clear what SWC shallow means or what the depth and resolution of SWC profile is. On the other hand, the manual soil sampling comes with a sampling depth. The presentation is quite heterogeneous.As the table currently stands, it looks rather like a fairground-like compilation of measurements. I understand that this is indeed the case to some extent, and this is how science develops, but I would recommend improving the look and feel.199How can the Inverse Distance Weighting procedure be justified if CRNS provides, as you claim yourself, an integrated signal? Or were the CRNS measurements not treated as point measurements?Figure 4What is the definition (and depth with variable land-use) of root-zone?217-247Odd citing of referencesWhat are all the details good for? Differences in detail as here give a very inhomogeneous impression.235what study?278"such as labor" - what is this supposed to mean?281different from that before"as tested by a Tukey test at alpha=0.05" is enough. But did you pair the locations as you should? With the proper pairing (~nesting) you might see a significant difference.284at tenThis is a method given at an inappropriate location. It is not clear how the other samples (results given before) were processed. It comes much too late. Impression evooqued: messy.303give a reference for FRM, please320explain CZglobe364It is not clear what you mean by crop type. Do you mean a crop functional type? An arable crop or species (it looks like this in line 366)? Or even a cultivar? lease specify.381240 measurements in one specific year? If you decided to be so specific you should also provide the year.427It rather impacts (or influences) water flow, otherwise we would not have to measure the unsaturated hydraulic conductivity in soil. And the boundary fluxes play also an important role (as you know, of course).429Durner (1994) referred to unsaturated hydraulic conditions, I suppose. Or do you mean "tedious" or "time-consuming"? The conductivity function is difficult to measure, not Ksat. In line with this statement, you indeed measured Ksat.456That sounds like glossing over the fact that no one bothered to compile and standardize a common data set.. I am not convinced that this is convenient for users.462refer469rather the "weather conditions" are at stake here472doubled sentence489() reference missing493Shouldn't you give also the size of the window? If it is the window from line 500, it comes to late there.499"3.6.", left over?505Explain N_0517reference desirableFigure 8The point 39 can hardly be seen, change colouring.517Explain what SWI means in relation to SWC, because this will play a role in the following.519, figure 83.4 km2 must be explained, also in the caption of figure 8. From figure 1 I understood that this is the total area (black line), but this does not really make sense here. Please resolve.In geography, it is good practice not to publish a map without a scale. I propose to add scales to the figures.519, 520I really appreciate your extensive measuring efforts to measure, but readers will rather find that in view of their clustering the sensor positions are not really well suited for aggregation. At least not in this case.******* End Review *******Citation: https://doi.org/10.5194/essd-2025-546-EC1
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The Potsdam Soil Moisture Observatory: High-coverage reference observations at kilometer scale Peter M. Grosse et al. https://doi.org/10.23728/b2share.db88e149f7924919be376909856739f1
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The Potsdam Soil Moisture Observatory: High-coverage reference observations at kilometer scale
Marret et al 2025
General comments
This is a great dataset and is worthy of publication so that it can be used to the benefit of many studies, particularly those looking to calibrate/validate satellite soil moisture products. The data is of a high quality and is generally well documented and easy to access.
The grammar needed a lot more work than was warranted and is disappointing as a reviewer given the large list of authors. I started making suggestions but gave up after L60 as it was far too distracting and time consuming. I note the quality improved dramatically beyond section 1 but still needs work. Please check everything carefully before resubmission. There are many tools to help with this.
This is worthy of publication after the grammar is fixed
Specific comments
L5- suggest “…for remote sensing algorithm validation due to its ability…”
L15 – suggest “The data are available from: https://doi.org/...”
L19 – rewrite the first sentence it is very hard to get past without rereading many times. Do you mean “Soil water storage varies spatially and temporally and is critical for understanding the water cycle, fluxes between the land surface and atmosphere…”?
L21 – what is an essential climate variable as defined by Bojinski? Sesntence needs explanation.
L25 –Fix grammar “The main challenges in soil moisture observation are…???”
L34 - suggest deleting “at very specific locations”
L52 – suggest changing to “…technology has proven to be a valuable method for intermediate…”
L58 – suggest "Neutron counts are typically accumulated over several hours, corrected for factors such as air pressure, and then converted to volumetric water content using a custom calibration function."
NOTE: after getting so frustrated with grammar and sentence structure I have not made any further grammar suggestions beyond this point as I think this is now beyond the role of a reviewer.
Fig 1 – can you make the site numbers a different colour like white so they can be read
L138 – are the TDT/FDR measurements field calibrated or are factory default calibration used? This is important as factory default values can be very poor
L173 –the instruments sold by Quaesta are made under licence from Hydroinnova – i.e. they are the same thing. It might be a different model but it’s the same technology
L185 – what correction approaches (pressure, vapour, intensity) and calibration equation have been applied to get soil moisture? NOTE – I now see this section 4 (maybe add a note that it is coming later)
L200 - A figure comparing the relative intensity of a couple of adjacent neutron sensors would be nice to see if they respond similarly
L227 – fix reference
L453 – were not removed?
L499 what does 3.6 mean?