the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Fog Monitoring through Machine Learning of Signal Attenuation Data from Microwave Links from Cellular Communication Networks
Abstract. Fog poses significant challenges in various sectors, from transportation safety to water resource management. Traditional fog detection methods rely on limited monitoring capabilities, hampering forecasting and nowcasting. This study investigates the potential of machine learning in fog classification based on microwave link signal attenuation data, utilizing existing commercial cellular communication networks. Using data from The Netherlands, the study explores machine learning models using the McFly model architecture. By incorporating multiple predictors including Received Signal Level (RSL) data, trends, and time variables, the models aim to distinguish fog from other weather phenomena. The research extends to a broader dataset from a commercial cellular network by using a reduced model and evaluates the feasibility of applying the reduced model on a larger scale. Results indicate promising prospects for machine learning in fog detection, with the Inception Time architecture showing notable accuracy in fog classification. However, challenges remain in balancing long and short-term data to align with fog evolution and reliably to distinguish fog from precipitation. Furthermore, the study suggests exploring higher-frequency telecommunication links for enhanced fog detection systems, emphasizing the need for continuous advancements in this domain.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-2634', Anonymous Referee #1, 09 Dec 2025
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RC2: 'Comment on egusphere-2025-2634', Anonymous Referee #2, 09 Jan 2026
General assessment
This manuscript presents an exploratory machine-learning analysis of fog-related attenuation patterns in commercial microwave links, using a previously published high-resolution dataset from Wageningen and a national dataset. The study is thoughtful, transparent about limitations, and relevant to the scope of AMT. However, several physical interpretation and methodological clarity issues must be addressed before the results can be interpreted by the authors. These issues are substantial but fixable, and I therefore recommend major revisions.
Major comments
1. Physical detectability of fog at 38 GHz
The manuscript does not quantify the expected magnitude of fog-induced microwave attenuation at 38 GHz. According to ITU-R P.840, typical fog liquid water contents (≈ 0.02–0.5 g m⁻³) correspond to specific attenuations of roughly 0.02–0.5 dB km⁻¹ at this frequency. For the 2.2 km Wageningen link, this implies total path attenuations for standard fog liquid water contents of 0.1 g.m-3 to be equal to 0.22 dB, which is comparable to instrumental effects and far smaller than wet-antenna attenuation. It has to be noted that some attenuation patterns during fog events are of magnitude of 4–5 dB (e.g. Figure 7, Figure 10)
This physical context is essential for interpreting the ML results, particularly the inconsistent detectability of fog events. I recommend explicitly adding ITU-R P.840–based attenuation estimates and clarifying that the ML models operate close to the physical sensitivity limit of the measurement system.
2. Wet-antenna attenuation (WAA) as a confounding mechanism
Wet-antenna attenuation is not explicitly discussed (it is not even mentioned in the manuscript) in the manuscript, despite being a known dominant attenuation mechanism at frequencies around 38 GHz. WAA can produce smooth, sustained attenuation during nighttime, drizzle, or post-rain conditions and cannot be distinguished from fog-induced path attenuation using RSL data alone.
Although precipitation is excluded using disdrometers, this does not eliminate WAA caused by antenna wetting, dew, or light drizzle. The ML models are not provided with inputs that allow physical separation of these effects. I recommend explicitly acknowledging WAA as a confounding factor and reframing general interpretations from “fog attenuation” or “fog detection” to “attenuation patterns associated with fog conditions” or similar
3. Scientific goal of the manuscript
If fog attenuation at 38 GHz is near the noise floor (comment #1) or hidden by WAA (comment #2), then almost any strong proxy for low visibility (traffic speed, incident reports, camera visibility, etc.) could beat it for “fog/not fog” prediction. The key question becomes: what is the scientific goal of the manuscript—detecting fog from CMLs (opportunistic sensing), or forecasting/detecting fog by any means? The manuscript tends to answer first question, but this is difficult without reflecting comment #1 and #2.
4. National-scale application (Section 3.4)
Section 3.4 applies the model to a nationwide microwave link dataset, but no spatial fog reference data exist for validation. Comparisons with nearby weather stations and radar provide plausibility but do not constitute quantitative validation.
I recommend relocating this section to the Discussion as an "exploratory national-scale application". This would prevent over-interpretation while preserving the illustrative value of the analysis.
In addition, I suggest explicitly stating at the beginning of the subsection that no quantitative validation is performed due to the absence of link-scale fog reference data, and that the purpose of the analysis is to demonstrate spatial coherence and feasibility rather than detection accuracy.
Methodological comments
5. Train/validation/test splitting and temporal leakage
The Wageningen dataset is randomly split into training, validation, and test subsets at 30 s resolution. Given the strong temporal persistence of fog, this allows adjacent timesteps from the same fog event to appear in all subsets, leading to temporal leakage. The reported metrics therefore reflect within-event interpolation rather than generalization to unseen events.
At minimum, this limitation should be explicitly discussed. If feasible, a time-blocked or event-based sensitivity analysis would strengthen the conclusions.
6. Dataset statistics and class balance
The manuscript does not report:
- the total number of 30 s timesteps,
- the number and fraction of fog-labelled timesteps,
- or the number of independent fog events.
Given the strong class imbalance and use of F1-score, these statistics are essential for reproducibility and interpretation.
Minor / clarity comments
7. Minor comments on abstract
- The mention of the McFly framework in the abstract could be replaced by a more general description of the applied machine-learning approach (e.g. “automated deep-learning time-series classification” or “AutoML-based deep learning”), with details on the specific software implementation provided later in the manuscript.
-The abstract concludes by suggesting the exploration of higher-frequency telecommunication links for enhanced fog detection. While this is a reasonable and widely discussed perspective, the present manuscript does not directly evaluate frequency dependence or provide quantitative evidence that higher frequencies would improve fog detectability. The argument appears primarily inferential, based on the observed limitations at 38 GHz and on prior literature. I therefore suggest relocating it entirely to ensure that the abstract strictly reflects results demonstrated within this study.
8. Definition of “channels”
The term “channel” in Section 2.4 refers to parallel CNN input feature streams of length 600 samples, with scalar predictors padded for compatibility. This should be stated explicitly to avoid confusion among readers unfamiliar with CNN terminology.
9. Minor comment on length and structure
The manuscript is relatively long compared to the strength of the quantitative validation. The clarity of the paper could be improved by condensing some of the case descriptions and/or relocating illustrative material to the Supplement or Discussion. This would help align the manuscript length more closely with the scope of the demonstrated results.
Citation: https://doi.org/10.5194/egusphere-2025-2634-RC2
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