the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Jan 2026
An Adjustable-Rate User-Printable Rain Gauge Calibrator
Abstract. Accurate precipitation measurement is essential. However, calibration of field-deployed rain gauges remains a challenge. Many methods require laboratory conditions, costly commercial equipment, or instruments designed for specific rain gauges, which cannot accommodate smaller-diameter gauges.
We introduce the Adjustable-Rate 3D Printed Rain Gauge Calibrator (AR3D), a low-cost, open-source device designed for in situ calibration of rain gauges.
The AR3D introduces three innovations: (1) an adjustable screw valve, enabling flow rate tuning from 0.15–16 mL min⁻¹, accommodating the lower flow rates needed for smaller rain gauges; (2) a compact and durable design developed with low-volume reservoirs and elimination of degradable parts; and (3) an integrated pyranometer cover to generate automatic calibration event signals.
We evaluated the AR3D using gravimetric tests, constant-rate stability tests, device-to-device equivalence tests, and field comparisons. Laboratory gravimetric tests of the AR3D demonstrate its ability to deliver volumes of water accurately with an average error of 0.11 % (comparable to ISO Class B tolerances for plastic volumetric flasks) at flow rates within ±5 % equivalence across independent devices, with a coefficient of variation (CV) below 5 %. The AR3D has been successfully deployed to weather stations in both Kenya and the United States. Field validation of the AR3D with a single setting resulted in a flow rate CV of 8.7 %. The AR3D enabled identification of properly functioning rain gauges, as well as an under-reporting station. The total cost of material and labor to build an AR3D is approximately USD 12.
- Preprint
(865 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 24 Jun 2026)
-
RC1: 'Comment on egusphere-2025-5744', Anonymous Referee #1, 10 Apr 2026
reply
-
AC1: 'Reply on RC1', Matthew Tippett-Vannini, 12 May 2026
reply
Dear Reviewer,
Thank you for your thorough and constructive review. We appreciate the time and care taken in evaluating this manuscript. Although the revised manuscript cannot be uploaded until a second reviewer is chosen, we responded to the first reviewer's comments and modified the original manuscript. Below we address each of the comments (reviewer’s comments are the section headers and authors’ responses are the main body):
Section 4.7: Temporal resolution and bucket tip counts
The METER group’s ATMOS 41 is a drip counter gauge, not a tipping bucket gauge. Nonetheless, we have added the 5-minute logging interval to the methods (Section 3.2) and calibration run times to the results (Section 4.2) in the revised manuscript.
Section 4.7: Details on how the gauge is calibrated
Because the ATMOS 41 is a drip counter gauge, it cannot be adjusted or recalibrated in situ. Adjustments can only be made by cleaning the measurement probes and funnel, factory recalibration, or data post-processing. We have added a brief description of the drip counter mechanism and clarified that the AR3D, for this type of gauge, serves as a diagnostic tool rather than a recalibration tool.
Section 4.7: Robust field validation and testing under multiple predefined flow rates
We believe that performance testing under controlled conditions using predefined flow rates was addressed in the laboratory results (Sections 4.1 in the revised manuscript), which characterize volumetric precision, flow rate range, rate constancy, single-device repeatability, and device-to-device equivalence. The field deployment (Section 4.2) demonstrates the AR3D intended diagnostic ability. The AR3D was tested on four independent gauges, under field conditions and successfully identified three functioning stations and one station requiring factory recalibration. We have revised the manuscript language to clarify this distinction between laboratory performance validation and field diagnostic demonstration.
Section 4.7: Extending tests to other low-cost gauges
We agree that extending tests to other gauge types would yield valuable insights. The AR3D's open-source design files are provided to facilitate adaptation to other gauges, though its adjustable rate makes it print-ready for many smaller gauges, without modifications. We have noted more explicitly, in the revised manuscript, that future work could include systematic evaluation across gauge types in a dedicated study.
Sections 2 and 3: Combine short subsections
Short subsections in Sections 2, 3, and 4 have been merged into cohesive sections in the revised manuscript.
Section 4.6: Pyranometer cover does not require a separate subsection
The pyranometer cover results have been integrated into the main results sections rather than presented as a standalone subsection.
Tables 1 and 2: Move to Appendix
Tables 1 and 2 have been moved to the Appendix in the revised manuscript.
Bibliographic entries
References have been checked and corrected for completeness and consistent formatting.
1, line 13: Convert flow rates to equivalent rainfall rates
Equivalent rainfall rates have been added. Flow rates in mL min⁻¹ were retained as well, since flow rate is independent of gauge funnel diameter.
3, line 1: Replace "document" with "article" or "manuscript"
Corrected.
6, line 141: Use SI units consistently
Corrected.
We thank the reviewer again for their comments, which improved the clarity of the manuscript. We look forward to continued discussions.
Best regards, Matthew Tippett-Vannini, on behalf of all co-authors
Citation: https://doi.org/10.5194/egusphere-2025-5744-AC1
-
AC1: 'Reply on RC1', Matthew Tippett-Vannini, 12 May 2026
reply
Data sets
AR3D Cleaned Calibration Dataset (Version 1.0) Matthew Tippett-Vannini https://doi.org/10.5281/zenodo.17642189
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 768 | 347 | 111 | 1,226 | 85 | 109 |
- HTML: 768
- PDF: 347
- XML: 111
- Total: 1,226
- BibTeX: 85
- EndNote: 109
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
In this manuscript, the authors present an adjustable‑rate, printable calibrator for field calibration of low‑cost rain gauges - a concept I find both elegant and meaningful. They describe modifications to a previous calibration device and report various test results for the modified calibrator with adjustable flow rates. Overall, the manuscript reads more like a technical note to me than a full research article; whether this fits the journal’s scope is, in my view, a decision for the editor(s). With this being said, I find the methods and results interesting and the manuscript in general suitable for publication. However, I have a few points for (minor to major) revision that should be addressed before final publication.
My main concern relates to the field evaluation in Section 4.7. Fist of all, it would be informative to specify the temporal resolution used for field calibration and whether the ATMOS 41 provides bucket‑tip counts per time interval or exact tip timestamps: Details on how this gauge is calibrated (presumably via a screw that adjusts the tipping point) could also be provided. Furthermore, demonstrating that the gauges in Kenya performed well while the one in the USA did not mainly shows that the latter was poorly maintained or malfunctioning, rather than providing a robust field validation of the AR3D. A more informative approach would be to test a set of well‑maintained, calibrated gauges under multiple predefined flow rates, thereby establishing the performance range under ideal conditions. This would be useful for identifying gauges in the field that require maintenance and/or recalibration. Extending such tests to other types of low‑cost gauges could also yield useful insights into the applicability and robustness of the AR3D.
Minor comments
- Sections 2 and 3 contain very short subsections and/or paragraphs, often limited to a single sentence or a table; these should be merged into longer, cohesive sections. Tables currently placed in Sections 2.3 and 2.4 could be moved in the Appendix.
- The “pyranometer cover” findings (4.6) do not require a separate subsection, this can be integrated into the results.
- Please check bibliographic entries for complete details and consistent citation formatting (including years).
Specific edits
- p. 1, line 13 - Convert the flow rates (ml min⁻¹) to equivalent rainfall rates.
- p. 3, line 1 - Replace “document” with “article” or “manuscript”.
- p. 6, line 141 - Use SI units consistently.