the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Sep 2026
Discretized thermodynamic imaging for the measurement of precipitation and winds
Abstract. Precipitation and winds impart spatially and temporally variable thermodynamic signatures on surfaces. Here, we describe two new hotplate sensors, the DTI-pm and DTI-de, that sample energy flows using a discretized thermodynamic imaging (DTI) principle. Unlike prior single-element hotplate devices, DTI measurements are obtained at sufficiently high spatial resolution to separate component thermodynamic signatures. The DTI-pm is a sensor array of individually controlled micro-hotplates, each using pulse-width modulation to maintain a constant elevated temperature of each sensor element, measuring the power required to do so. The DTI-de uses an infrared camera that passively monitors radiative temperatures on a heated metal plate by exploiting the differential emissivity between metal and water; heat transfer physics is used to infer the power of thermodynamic cooling. Both techniques are shown here to be capable of measuring with exceptionally high accuracy and precision a wide range of precipitation characteristics, including mass, size, and the density of individual multi-phase hydrometeors, as well as continuous bulk precipitation rates and snow density. The DTI-de achieves a spatial resolution of 0.2 mm with a mass sensitivity of 1 µg, while the DTI-pm provides a spatial resolution of 1 mm and a mass sensitivity of 0.5 µg. Preliminary results suggest the potential for the DTI-pm and DTI-de to concurrently measure wind speed and direction.
Competing interests: The DTI-de and DTI-de technologies are protected through US patents 11674878 and 11640013 including authors D.K.S., E.R.P., and T.J.G.. They are commercially available through Particle Flux Analytics, Inc. (PFA) of which A.T.R and T.J.G. are co-founders. PFA has a license from the University of Utah to commercialize DTI devices.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-3996', Anonymous Referee #1, 02 Oct 2026
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RC2: 'Comment on egusphere-2026-3996', Anonymous Referee #2, 25 Oct 2026
General comments
The manuscript describes an innovative instrument for measuring atmospheric precipitation and wind based on thermodynamics. This refined version of the existing hotplate sensor can measure individual heat transfer signals over an array of small sensors, rather than providing a single integral response over a continuous surface. This enables individual hydrometeors to be sensed, providing both microphysical and bulk precipitation properties. The authors have patented the implemented solution and have a declared commercial interest in demonstrating its performance against other commercially available measurement instruments.The instrument, as described, is still in the early stages of development and its performance in terms of accuracy, sensitivity and robustness for field applications has yet to be fully quantified. Nevertheless, it appears to have considerable potential and will certainly be of interest to the scientific community. The topic also aligns well with the scope of the journal.
The manuscript does not address relevant aspects of instrument performance and the impact of potential sources of measurement bias from environmental and instrumental factors, even though these may be significant and should at least be mentioned (also because the authors mention them as limitations in reference to existing sensors). For example, the impact of raindrops splashing on the surface probably skews the measured drop size distribution towards smaller diameters, and this should be discussed in the manuscript. This effect may be partially counterbalanced by the lower limit of detection for the smallest hydrometeors.
Regarding wind measurements, the aerodynamic behaviour of the sensor may limit how representative its measurements are of undisturbed wind speed and direction. The instrument body is quite bulky, so an aerodynamic design may be necessary. This may also affect precipitation measurements by deflecting hydrometeors away from the sensing plate, and this should be discussed in the manuscript. In particular, the measurement of turbulence, which is mentioned as a possible future development, would be affected by the aerodynamics of the instrument (wouldn’t the sensor measure turbulence caused by the wind interacting with the body of the instrument rather than the turbulence inherent in the undisturbed wind field?). Finally, is wind direction a factor in determining the sensor’s accuracy? While the body of the instrument is indeed radially symmetric (except for the supporting arm), the sensing area is not.
The overall dimensions of the sensor array (26.4 x 26.4 mm) are given without any explanation of the reasons behind this choice. I would guess that it is a compromise between cost and performance, but readers should be explicitly informed of any considerations that led to the chosen size, and of any sensitivity analyses performed. Was the size of the array also chosen based on considerations regarding the representativeness of the drop size distribution, and is there a minimum size required?
The Conclusions section should be totally revised to include concluding remarks rather than listing a summary of the work done, which is the role of the Abstract, and avoiding unsubstantiated statements.
In my opinion, the manuscript would benefit from moderate review, and the authors should address the important points mentioned above and in the following detailed comments.
Detailed comments
Abstract – lines 1 to 3: acronyms are used before they are defined. The sentence “Here, we describe two new hotplate sensors, the DTI-pm and DTI-de, that sample energy flows using a discretised thermodynamic imaging (DTI) principle” should be modified to read, for example, “Here, we describe two new hotplate sensors that sample energy flows using a discretised thermodynamic imaging (DTI) principle: the power modulated (DTI-pm) and differential emissivity (DTI-de) sensors”.Abstract – line 8: “exceptionally high” is too strong a statement regarding the performance of the new instrument as described in the manuscript. I suggest replacing “exceptionally high” with “good” or “promising”.
Abstract – lines 8-9: The term “accuracy and precision” is not entirely clear, since “accuracy” is a qualitative concept that is generally considered to be the result of trueness and precision. I suggest using just “accuracy” instead of “accuracy and precision”.
Introduction – The discussion about the limitations of existing precipitation measurement instruments is very brief, whereas the proposal of new sensors requires more detailed justification. There is no report on the current quantitative performance of tipping-bucket and weighing gauges (for example according to the European Standard EN 17277:2019), and the reasons why they should be replaced by new sensors are too generic. The introduction should be substantially expanded to include more quantitative details about the performance of precipitation and wind sensors based on existing technologies. In particular, the performance of the existing hotplate sensor should be addressed more specifically, since the proposed sensors use the same physical principle. Wind sensors are not mentioned at all in the introduction, even though the proposed new sensors aim at measuring wind speed and direction as well.
Introduction – line 19: same as above. I suggest using “accuracy” instead of “accuracy and precision”.
Introduction – lines 28-29: the accuracy of the Parsivel2 optical disdrometer is exaggerated by claiming that the instrument can measure rainfall with “high accuracy”, whereas Chinchella et al. (2026) – see DOI: 10.1016/j.atmosres.2026.108865 – demonstrated that the relative percentage bias can exceed 10% when measuring rainfall intensity from 10 to 100 mm/h.
Introduction – line 39: the existing hotplate sensor is sensitive not only to high winds during low precipitation rates, but also to low winds (below 5 m/s) and significant snowfall rates (above 10 mm/h). In these conditions, wind-induced undercatch can be in the order of 10–15% (see, for example, DOI: 10.1175/JHM-D-20-0149.1).
Introduction – line 45: same as above. I suggest using “accuracy” instead of “accuracy and precision”.
3 Laboratory evaluation: No reference is made to standardized laboratory tests for determining the accuracy of disdrometers, such as the European Standard EN 18097:2025.
3.1 Particle mass – line 120: “droplets of 6mm diameter that are unlikely to be encountered in the field”. Field experiments using disdrometers generally report of a significant number of raindrops of diameter equal or greater than 6mm, up to 8mm (see e.g., DOI: 10.5194/adgeo-16-11-2008; 10.1007/s13351-026-5128-3). Please reconsider this statement in view of the available observations of the drop size distribution in natural rain.
3.1 Particle mass – line 125: the acronym SLR (Single Lens Reflex) should be defined.
Figure 3 – caption: the sentence “The coefficients of determination are 0.999 for DTI-pm and 0.998 for DTI-de” should be deleted from the caption since this numerical information is already given in the graph.
3.2 Wind speed – line 139-147: The text reads “The relationship between the dimensionless Nusselt number (Nu) for heat loss and the dimensionless Reynolds number (Re)” (…) “is:”, but the following equations (2) and (3) are just the definitions of the Nusselt and Reynolds numbers, respectively. The obtained relationship between the two is given later in Equation (4). Please modify the text in this paragraph to be consistent with the equations listed and replace ‘this’ with ‘the’ in line 147.
3.2 Wind speed – line 150: “transducer” should be “transducers”.
4 Field tests – line 209: I suggest replacing “somewhat surprising” with “significant”.
4 Field tests – line 216: There is a missing space between “disdrometer” and “(Löffler-Mang and Joss, 2000)”.
Figure 12: please include a legend to indicate the meaning of the continuous blue line and the red dots.
5 Conclusions – lines 237-241: This paragraph is not a conclusion but rather a repetition of concepts already expressed in the Introduction. Please remove this paragraph from the Conclusions section.
5 Conclusions – lines 244-249: This paragraph is not a conclusion but rather a summary of the content of the manuscript, which is usually done in the Abstract. Please remove this paragraph from the Conclusions section.
5 Conclusions – lines 251-252: The agreement found in one specific experiment between the snow depth derived from the measurements taken by the sensor and other measurements of the snow depth on the ground is not indicative of a generalised capability of the sensor to infer (rather than measure) snow depth. Please use more cautious statements on this aspect.
5 Conclusions – lines 252: The authors claim that “both devices demonstrate higher sensitivity and accuracy than existing standard precipitation and snowpack measurement technologies”. This statement is totally unsubstantiated. No part of the work presented in the manuscript addresses the accuracy of the proposed measurement instrument, let alone compares it with the accuracy of other technologies. The case studies presented compare some measurements obtained from the proposed sensors with those from other arbitrarily chosen instruments, with no systematic or rigorous approach to their measurement accuracy. Please remove this sentence, as the manuscript provides no results that would support the statement.
5 Conclusions – lines 256: “It may be possible...” is a hypothetical formulation that is not supported by the manuscript and should not be used. I suggest replacing it with something like “Further work is underway to explore the suitability of the proposed technology for...”.
Acknowledgements – line 270: One of the manuscript's authors is acknowledged for contributing to the development of the sensors and for leading the sensor development project. This is already mentioned in the “Author Contributions” section, so there is no need to repeat it in the acknowledgements.
References: The style is not uniform, and the DOI is sometimes missing. Please revise the reference style according to the journal's guidelines and include the DOI wherever possible.
Citation: https://doi.org/10.5194/egusphere-2026-3996-RC2
Data sets
Laboratory and Field Validation Data for Discretized Thermodynamic Imaging Measurements of Precipitation and Winds T. J. Garrett, E. R. Pardyjak, and D. S. Singh https://hive.utah.edu/records/nxsf5-z6814
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- 1
This study presents two new devices for measuring the microphysical properties of solid precipitation. The manuscript describes a novel approach that uses technology similar to that employed in hotplate precipitation gauges, but on the scale of single particles. This approach has the potential to improve the characterisation of precipitation particle properties. Field measurements obtained using these new devices can also be used to improve models. The manuscript is well written, and I have only minor comments.
Abstract, line 12: I am wondering why “preliminary results”, I believe that a manuscript should present results, even if only partial data is available.
Line 39, It is mentioned that the 'hotplate precipitation gauge' requires maintenance, but that it is lower maintenance compared to other weighting gauges as it does not need to be emptied regularly, for example. The authors should modify the sentence to clarify the nature of the maintenance issues.
Section 2, 1st paragraph: The author may wish to note that this technology is similar to the hotplate precipitation gauge developed by Rasmussen et al. in 2011. The difference is that the hotplate precipitation gauge measures the total amount of precipitation, whereas the DTI measures it on a particle-by-particle basis. This should be clarified here.
Line 57: “… T0 = 0C is the freezing temperature…” This is confusing because water drops usually start to freeze at lower temperatures than 0C. In contrast, ice particles would melt at a wet bulb temperature of 0°C. Could you please clarify what T0 is?
Line 79: there is a typo at the end of the line: “ An added ability is o automatically…” “o should be deleted”
Line 92: “… temperature of evaporating droplets on a heated metal…” should it be “hydrometeors” to include ice particles as well? Or does this only apply to liquid particles?
Line 115: “…with masses ranging from 2 mg to nearly 200 mg were…” It would be helpful to add the size of the particles as well.
Line 119: “The largest tested drops of 120 mg covered the entire array, …” that value is different than the one line 115.
Figure 4 is missing...
Line 136: “At a basic physical level, …” that is needed?
Line 174-175: “While not described here, the rapid… turbulence.” Given that it is not elaborated on in the manuscript, I am wondering if that sentence is needed. Should it be deleted?
Figure 6: The definition of the masses indicated on panel a is not provided in the figure caption. Could it be added?
Line 192: The tipping bucket rain gauge tends to underestimate solid precipitation. A sentence and reference (e.g. Rasmussen et al., 2011) should be added to discuss that uncertainty in the measurements?
Rasmussen, R., B. Baker, J. Kochendorfer, T. Meyers, S. Landolt, A. P. Fischer, J. Black, J. M. Thériault, P. Kucera, D. Gochis, C. Smith, R. Nitu, M. Hall, K. Ikeda, et E. Gutmann (2012), How well are we measuring snow: The NOAA/FAA/NCAR winter precipitation testbed. BAMS, 93, 811-829. http://dx.doi.org/10.1175/BAMS-D-11-00052.1
Line 208: I suggest reformulating the following sentence, as the meaning of 'surprising' is unclear. 'The degree to which continuous DTI-de... snowpack.' It could be, 'The DTI-de agrees relatively well with manual measurements, despite the fact that...'
Line 240: The authors mentioned that 'Previous hotplate designs have suffered from unresolved environmental influences on the signal and only provide single-point measurements.' While the first part of the sentence is probably correct, I believe that the DTI also only provides one-point measurements unless multiple sensors are deployed at different locations. The authors should add a few sentences to clarify this. They should also specify whether the DTI can be powered by batteries or solar panels. They explained the power requirement, but I don’t think that it has been specify explicitly.
Acknowledgements: One of the co-authors, Allan T. Reaburn, is acknowledged in the section. I suggest that the authors modify the acknowledgements section so that the same person does not appear in both that section and as a co-author.