Commercial microwave links as a tool for operational rainfall monitoring in Northern Italy

Abstract

Abstract. There is a growing interest in emerging opportunistic sensors for precipitation, motivated by the need to improve its quantitative estimates at the ground. The scope of this work is to present a preliminary assessment of the accuracy of commercial microwave link (CML) retrieved rainfall rates in Northern Italy. The CML product, obtained by the open-source RAINLINK software package, is evaluated on different scales (single link, 5 km×5 km grid, river basin) against the precipitation products operationally used at Arpae-SIMC, the regional weather service of Emilia-Romagna, in Northern Italy. The results of the 15 min single-link validation with nearby rain gauges show high variability, which can be caused by the complex physiography and precipitation patterns. Known sources of errors (e.g. the attenuation caused by the wetting of the antennas or random fluctuations in the baseline) are particularly hard to mitigate in these conditions without a specific calibration, which has not been implemented. However, hourly cumulated spatially interpolated CML rainfall maps, validated with respect to the established regional gauge-based reference, show similar performance (R2 of 0.46 and coefficient of variation, CV, of 0.78) to adjusted radar-based precipitation gridded products and better performance than satellite-based ones. Performance improves when basin-scale total precipitation amounts are considered (R2 of 0.83 and CV of 0.48). Avoiding regional-specific calibration therefore does not preclude the algorithm from working but has some limitations in probability of detection (POD) and accuracy. A widespread underestimation is evident at both the grid box scale (mean error of −0.26) and the basin scale (multiplicative bias of 0.7), while the number of false alarms is generally low and becomes even lower as link coverage increases. Also taking into account delays in the availability of the data (latency of 0.33 h for CML against 1 h for the adjusted radar and 24 h for the quality-controlled rain gauges), CML appears as a valuable data source in particular from a local operational framework perspective. Finally, results show complementary strengths for CMLs and radars, encouraging joint exploitation.

Wildfire Smoke Particulate Matter Concentration Measurements Using Radio Links From Cellular Communication Networks

“…One barrier to a more generalized used of CML data is the potentially wider availability of such privately owned data sets: there remains a large variability in the conditions of access to such data. In the present case data was accessible to the authors but protected by a Non-Disclosure agreement, as seen also in Graf et al (2020), while in others the data is freely available (de Vos et al, 2018a) or available upon purchase (Roversi et al, 2020). The uniqueness of CML data is their worldwide distribution, and the presence of infrastructure collecting data in remote and unmonitored regions where other techniques are unavailable.…”

Precipitation Estimates from Commercial Microwave Links: Practical Approaches to Wet-antenna Correction

“…As it was noted by [11], maintenance of dedicated equipment for retrieval of the needed reference rainfall observations is impractical for such networks. Thus, application-focused studies with city or regional-scale CML networks have often not applied any WAA correction at all [12], [13] or have used only a simple constant offset model [3], [14], [15], [16]. Although the latter approach may be a reasonable choice when only 15-min TRSL maxima and minima are available [2], it can introduce a considerable bias in the resulting CML QPEs [3], [17].…”

“…In this study, we analyze for the first time six empirical WAA models, including a newly proposed one, based on considerably different assumptions and test in detail their performance. In contrast to previous studies, often limited by a low number of CMLs investigated [4], [7], [10], short time series of a few months [7], [14], [15] or 15-min CML data sampling intervals [14], [19], we use a rich dataset of more than two years of data retrieved from 16 CMLs with a sub-minute sampling rate. Motivated by the vision of reducing the costs of future studies with high numbers of CMLs, we also address the previously recognized need [11], [18] to minimize the amount of auxiliary data necessary for WAA estimation without compromising the quality of retrieved QPEs, and thus, we introduce three conceptual innovations not previously presented in relevant literature: Firstly, we show how the investigated empirical WAA models can be calibrated while notably minimizing the requirements on the reference rainfall data necessary, i.e.…”

Hydrological response of a peri-urban catchment exploiting conventional and unconventional rainfall observations: the case study of Lambro catchment

“…Authors found out that the bias propagated thoughout simulations is inversely proportional to CML length. In Italy, Roversi et al (2020) conducted a meteorological analysis in the Po valley in Emilia Romagna (northern Italy) to assess the accuracy of CML retrieved rainfall rates using data purchased from Vodafone.…”