Christian Chwala

Karlsruhe Institute of Technology | KIT · Institute of Meteorology and Climate Research

Environmental sensor networks play a crucial role in monitoring key parameters essential for understanding Earth’s systems. To ensure the reliability and accuracy of collected data, effective quality control (QC) measures are essential. Conventional QC methods struggle to handle the complexity of environmental data. Conversely, advanced techniques...

Two simple feedforward neural networks (multilayer perceptrons – MLPs) are trained to detect rainfall events using signal attenuation from commercial microwave links (CMLs) as predictors and high-temporal-resolution reference data as the target. MLPGA is trained against nearby rain gauges, and MLPRA is trained against gauge-adjusted weather radar....

The spatial and temporal distribution of precipitation has a significant impact on human lives by determining freshwater resources and agricultural yield, but also rainfall-driven hazards like flooding or landslides. While the ERA5 reanalysis dataset provides consistent long-term global precipitation information that allows investigations of these...

Differentiating between snow and rainfall is crucial for hydrological modeling and understanding. Commercial Microwave Links (CMLs) can provide accurate rainfall estimates for liquid precipitation, but show minimal signal attenuation during dry snow events, causing the CML time series during these periods to resemble non-precipitation periods. Weat...

The need to develop and provide integrated observation systems to better understand and manage global and regional environmental change is one of the major challenges facing Earth system science today. In 2008, the German Helmholtz Association took up this challenge and launched the German research infrastructure TERrestrial ENvironmental Observato...

Environmental sensor networks play a crucial role in monitoring key parameters essential for understanding Earth's systems. To ensure the reliability and accuracy of collected data, effective quality control (QC) measures are essential. Conventional QC methods struggle to handle the complexity of environmental data. Conversely, advanced techniques...

The most reliable areal precipitation estimation is usually generated via combinations of different measurements. Path-averaged rainfall rates can be derived from commercial microwave links (CMLs), where attenuation of the emitted radiation is strongly related to rainfall rate. CMLs can be combined with data from other rainfall measurements or can...

Two simple feedforward neural networks (MLPs) are trained to classify wet and dry periods using signal attenuation from commercial microwave links (CMLs) as predictors and high temporal resolution reference data as target. MLPGA is trained against nearby rain gauges and MLPRA is trained against gauge-adjusted weather radar. Both MLPs perform better...

Weather radars are highly sophisticated tools for quantitative precipitation estimation and provide observations with unmatched spatial representativeness. However, their indirect measurement of precipitation high above ground leads to strong systematic errors compared to direct rain gauge measurements. Additionally, the temporal undersampling from...

The need to develop and provide integrated observation systems to better understand and manage global and regional environmental change is one of the major challenges facing Earth system science today. In 2008, the German Helmholtz Association took up this challenge and launched the German research infrastructure TERrestrial ENvironmental Observato...

Opportunistic sensors are increasingly used for rainfall measurement. However, their raw data are collected by a variety of systems that are often not primarily intended for rainfall monitoring, resulting in a plethora of different data formats and a lack of common standards. This hinders the sharing of opportunistic sensing (OS) data, their automa...

Climate models face limitations in their ability to accurately represent highly variable atmospheric phenomena. To resolve fine-scale physical processes, allowing for local impact assessments, downscaling techniques are essential. We propose spateGAN, a novel approach for spatio-temporal downscaling of precipitation data using conditional generativ...

Opportunistic sensors are increasingly used for rainfall measurement. However, their raw data are collected by a variety of systems that are often not primarily intended for rainfall monitoring, resulting in a plethora of different data formats and a lack of common standards. This hinders the sharing of opportunistic sensing (OS) data, their automa...

The most reliable areal precipitation estimation is usually generated via combinations of different measurements and devices by merging their individual advantages. Path-averaged rain rate can be derived from Commercial Microwave Links (CML), where attenuation of the emitted radiation is strongly related with rainfall rate. CMLs can be combined wit...

Plain Language Summary Rainfall maps are usually based on gauge observations on the ground or radar. They are crucial for predicting or reconstructing flooding events. Commercial microwave links are special kinds of rainfall sensors. Their actual purpose is the signal propagation within a cellular network. However, since the signal is attenuated wh...

We present high-resolution rainfall maps from commercial microwave link (CML) data in the city of Ouagadougou, Burkina Faso. Rainfall was quantified based on data from 100 CMLs along unique paths and interpolated to achieve rainfall maps with a 5-min temporal and 0.55-km spatial resolution for the monsoon season of 2020. Established processing meth...

Climate models face limitations in their ability to accurately represent highly variable atmospheric phenomena. To resolve fine-scale physical processes, allowing for local impact assessments, downscaling techniques are essential. We propose spateGAN, a novel approach for spatio-temporal downscaling of precipitation data using conditional generativ...

Unlike actual rainfall, the spatial extent of rainfall maps is often determined by administrative and political boundaries. Similarly, data from commercial microwave links (CMLs) is usually acquired on national basis and exchange among countries is limited. Up to now, this has prohibited the generation of transboundary CML-based rainfall maps despi...

Plain Language Summary Commercial microwave links (CMLs) are used to transmit information between towers of cellphone networks. If there is rainfall along the transmission path, the signal level is attenuated. By comparing the transmitted and received signal levels, the average rainfall intensity along the path can be estimated. If the attenuation...

Wet antenna attenuation (WAA) can cause significant overestimation of rainfall estimates from commercial microwave link (CML) data. Typically, WAA estimation is done by comparing CML rainfall estimates to reference data and attributing the residual to WAA. Due to different spatio-temporal integration characteristics of CML and reference observation...

Since the 1990s, mobile telecommunication networks have gradually become denser around the world. Nowadays, large parts of their backhaul network consist of commercial microwave links (CMLs). Since CML signals are attenuated by rainfall, the exploitation of records of this attenuation is an innovative and an inexpensive solution for precipitation m...

Climate change is one of the greatest challenges in Sub-Saharan Africa. Projections suggest that an increasingly variable occurrence of precipitation and rising temperatures will lead to considerable harvest losses. With traditional rain-fed agriculture, extreme variability in precipitation and frequent droughts and floods, food production in Sub-S...

Plain Language Summary Rainfall is commonly measured by dedicated sensors such as rain gauges or weather radars. Commercial microwave links (CMLs), which have the primary purpose of signal forwarding within cellular networks, can be used for rainfall measurements too. The signal, which is transmitted from one antenna to another, is being attenuated...

Since the 1990s, mobile telecommunication networks have gradually become denser around the world. Nowadays, large parts of their backhaul network consist of commercial microwave links (CMLs). Since CML signals are attenuated by rainfall the exploitation of records of this attenua-tion for precipitation monitoring purposes is an innovative and inexp...

A new hydro-meteorological precipitation and flood forecasting system for small catchments

Near-surface humidity is a crucial variable in many atmospheric processes, mostly related to the development of clouds and rain. The humidity at the height of a few tens of meters above ground level is highly influenced by surface characteristics. Measuring the near-surface humidity at high resolution, where most of the humidity’s sinks and sources...

An important aspect of rainfall estimation is to accurately capture extreme events. Commercial microwave links (CMLs) can complement weather radar and rain gauge data by estimating path-averaged rainfall intensities near ground. Our aim with this paper was to investigate attenuation induced total loss of signal (blackout) in the CML data. This effe...

The availability of rainfall data is essential for the prediction of extreme rainfall events, hydrological modeling, and the design of water resources systems. In Palestine, the limited available rain gauges and the available rainfall data are insufficient to precisely characterize the areal rainfall distribution over the entire area. Hence, it is...

Climate change is one of the greatest challenges in Sub-Saharan Africa. Projections suggest that an increasingly variable occurrence of precipitation and rising temperatures will lead to considerable harvest losses of up to 50%. This is affecting the African agricultural sector, including Burkina Faso, a country where the agricultural sector plays...

Study region: The study region is Germany and two sub-regions in Germany, i.e. the state of Rhineland-Palatinate and the city of Reutlingen. Study focus: Opportunistic rainfall sensors, namely personal weather stations and commercial microwave links, together with rain gauge data from the German Weather Service, were used in different combinations...

We can observe a global decrease of well maintained weather stations by meteorological services and governmental institutes. At the same time, environmental sensor data is increasing through the use of opportunistic or remote sensing approaches. Overall, the trend for environmental sensor networks is strongly going towards automated routines, espec...

During the last years we made great progress with the country-wide rainfall estimation from commerical microwave link (CML) data in Germany (Graf et al. 2020, Polz et al. 2020). Using the derived results in different applications has, however, revealed that undetected erratic behaviour of CML raw data is still limiting data quality and that data ga...

Zusammenfassung Das möglichst exakte Erfassen des Niederschlags ist ein grundlegender Bestandteil der Klima‐ und Umweltforschung sowie für verschiedene Anwendungen, beispielsweise in der Landwirtschaft. Eine neue Art der Niederschlagsmessung ermöglicht das Mobilfunknetz in Deutschland mittels Richtfunkstrecken (Commercial Microwave Link, CML). Der...

Using signal level measurements from commercial microwave links (CMLs) has proven to be a valuable tool for near-ground 2-D rain mapping. Such mapping is commonly based on spatial interpolation methods, where each CML is considered as a point measurement instrument located at its center. The validity of the resulted maps is tested against radar obs...

Commercial microwave links (CMLs) can be used for quantitative precipitation estimation (QPE) by exploiting the close to linear relationship between path-integrated attenuation and path-averaged rain rate. Currently, attenuation data from 3904 CMLs in Germany is obtained in real-time, with 3 years of collected data. We have carried out a first larg...

Quantitative precipitation estimation with commercial microwave links (CMLs) is a technique developed to supplement weather radar and rain gauge observations. It is exploiting the relation between the attenuation of CML signal levels and the integrated rain rate along a CML path. The opportunistic nature of this method requires a sophisticated data...

Rainfall is one of the most important environmental variables. However, it is a challenge to measure it accurately over space and time. During the last decade, commercial microwave links (CMLs), operated by mobile network providers, have proven to be an additional source of rainfall information to complement traditional rainfall measurements. In th...

Commercial microwave links (CMLs) can be used for quantitative precipitation estimation. The measurement technique is based on the exploitation of the close to linear relationship between the attenuation of the signal level by rainfall and the path averaged rain rate. At a temporal resolution of one minute, the signal level of almost 4000 CMLs dist...

In recent years, so-called opportunistic sensors for measuring rainfall, are attracting more notice due to their broad availability and low financial effort for the scientific community. These sensors are existing devices or infrastructure, which were not intentionally built to measure rainfall, but can deliver rainfall information. One example of...

Attenuation data from microwave links can be used to derive important near-ground precipitation estimates which complements observations from rain gauges and weather radars. Wetness on the cover of the microwave link antennas can, however, lead to additional attenuation, resulting in an overestimation of rainfall rates. To investigate the impact of...

Quantitative precipitation estimation with commercial microwave links (CMLs) is a technique developed to supplement weather radar and rain gauge observations. It is exploiting the relation between the attenuation of CML signal levels and the integrated rain rate along a CML path. The opportunistic nature of this method requires a sophisticated data...

Rainfall is one of the most important environmental variables. However, it is a challenge to measure it accurately over space and time. During the last decade commercial microwave links (CMLs) operated by mobile network providers have proven to be an additional source of rainfall information to complement traditional rainfall measurements. In this...

This letter presents an analysis of wet antenna attenuation (WAA) from an electrodynamic perspective. The WAA is a relevant part of the path attenuation determined from the received signal level (RSL). In the case of extracting rain rates from path attenuation, as it is done with data from country-wide commercial microwave link (CML) networks, the...

Precipitation estimation remains a scientific challenge, because of the high variability of precipitation in space and time. Traditional precipitation measurements have well known drawbacks: Gauge measurements are prone to wind induced errors and lack spatial representativeness. Weather radars overcome this spatial constraint, but depend on the non...

Accurate observation of the high spatio‐temporal variability of rainfall is crucial for hydrometeorological applications. However, the existing observations from rain gauges and weather radars have individual shortcomings that can introduce considerable errors and uncertainties. A fairly new technique to get additional rainfall information is the u...

The cover image is based on the Advanced Review Commercial microwave link networks for rainfall observation: Assessment of the current status and future challenges, by Christian Chwala and Harald Kunstmann, https://doi.org/10.1002/wat2.1337 The cover image is based on the Advanced Review Commercial microwave link networks for rainfall observation:...

Core Ideas Pre‐alpine areas face more intense warming and extreme hydrological events than the global average. Climate and land management change have far‐reaching impacts on ecosystem functions and services. We have improved knowledge of water, energy, and matter exchange by long‐term observations and modeling. Global change has triggered several...

For the reconstruction and interpolation of precipitation fields we present the application of a stochastic approach called Random Mixing. Generated fields are based on a dataset consisting of rain gauge observations and path averaged rain rates estimated using Commercial Microwave Link (CML) derived information. Precipitation fields are received a...

Augmenting long-term ecosystem-atmosphere observations with multidisciplinary intensive campaigns aims at closing gaps in spatial and temporal scales of observation for energy- and biogeochemical cycling, and at stimulating collaborative research. ScaleX is a collaborative measurement campaign, co-located with a long-term environmental observatory...

The number of rain gauges is declining worldwide. A recent promising method for alternative precipitation measurements is to derive rain rates from the attenuation of the microwave signal between remote antennas of mobile phone base stations, so called commercial microwave links (CMLs). In European countries, such as Germany, the CML technique can...

Commercial microwave link networks allow for the quantification of path integrated precipitation because the attenuation by hydrometeors correlates with rainfall between transmitter and receiver stations. The networks, operated and maintained by cellphone companies, thereby provide completely new and country wide precipitation measurements. As the...

FIRST INTERNATIONAL WORKSHOP ON RAINFALL MEASUREMENT FROM CELLULAR PHONE NETWORKS IN AFRICA (RAIN CELL AFRICA) What: Eighty-seven participants from 18 countries met to discuss the prospect for rainfall measurement and high-resolution mapping based on commercial microwave links in Africa. Experts from Europe and Israel provided training to African s...

This thesis first summarizes the theory of the interaction of microwave radiation with precipitation and humidity. It further describes the development and operation of a microwave transmission experiment and analyzes its data to derive information about humidity and rainfall. In addition, a new method to process attenuation data from commercial mi...

The improved understanding of the interlinked atmospheric and terrestrial hydrological processes requires concerted and compartment-crossing observation and -modeling efforts. Through the TERENO preAlpine Observatory, located in the southern Bavarian region of Germany, comprehensive technical infrastructure is being established to allow joint analy...

The usage of data from commercial microwave link (CML) networks for scientific purposes is becoming increasingly popular, in particular for rain rate estimation. However, data acquisition and availability is still a crucial problem and limits research possibilities. To overcome this issue, we have developed an open source data acquisition system ba...

The variability in raindrop size distributions and attenuation effects are the two major sources of uncertainty in radar-based quantitative precipitation estimation (QPE) even when dual-polarization radars are used. New methods are introduced to exploit the measurements by commercial microwave radio links to reduce the uncertainties in both attenua...

Near-surface water vapor and precipitation are central hydrometeorological observables which are still difficult to quantify accurately above the point scale. Both play an important role in modeling and remote sensing of the hydrologic cycle. We present details on the development of a new microwave transmission experiment that is capable of providi...

Detection of precipitation based on the received signal level of commercial microwave links has been increasingly used in the mountain areas where meteorological radars have limited ranges, and placing rain gauges is impossible due to terrain morphology. In this paper, focused time-delay neural networks were trained to detect the appearance of prec...

Detection of precipitation based on the received signal level of commercial microwave links has been increasingly used in the mountain areas where meteorological radars have limited ranges, and placing rain gauges is impossible due to terrain morphology. In this paper, focused time-delay neural networks were trained and tested, to detect the appear...

Measuring rain rates over complex terrain is afflicted with large uncertainties, because rain gauges are influenced by orography and weather radars are mostly not able to look into mountain valleys. We apply a new method to estimate near surface rain rates exploiting attenuation data from commercial microwave links in the alpine region of Southern...

This article presents extensions of a numerical technique to model electromagnetic propagation through rain. Embedded in the Helmholtz Virtual Institute “Regional Precipitation Observation by Cellular Network Microwave Attenuation and Application to Water Resources Management” (PROCEMA) the method serves as theoretical basis for a novel method to m...

Rain rate observation over complex terrain is still afflicted with large uncertainties introduced by system inherent drawbacks of radar and gauge measurements. We use a new method for near surface rain rate estimation exploiting attenuation data from commercial microwave backhaul links. Our test region is the pre-alpine and alpine region of Souther...

Measuring rain rates over complex terrain is afflicted with large uncertainties. Rain gauges are increasingly affected by wind and exposure induced errors and weather radar measurements in mountainous regions are hampered by beam blockage and enhanced bright band interception. We present results from a new method to estimate near surface rain rates...

This work presents strategies to significantly improve the numerical efficiency and the accuracy of a simulator for electromagnetic scattering by rain which considers every single rain drop within a given volume. By also considering power extinction the rain-rate dependent signal attenuation is modeled in addition to the rain-rate dependent noise....

During the TERENO campaign in May/June 2011 fully polarimetric L-band airborne SAR data was acquired by DLR’s novel F-SAR sensor. The measurements were performed for the TERENO test sites “Ammer Catchment - Fendt” (part of the Bavarian Alps/pre-Alps observatory), “Bode Catchment - Schäfertal” (part of the Harz/Central Lowland Observatory) and the “...

Measuring rain rates over complex terrain is afflicted with large uncertainties because rain gauges are influenced by orography and weather radars are mostly not able to look into mountain valleys. We apply a new method to estimate near surface rain rates exploiting attenuation data from commercial microwave links in the alpine region of Southern G...