| 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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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.