Comment on amt-2022-193

Wind is a core state variable of the atmosphere. Extending the capabilities of ground-based measurement systems, airborne Doppler lidar (ADL) onboard research aircraft allows for targeted and spatially resolved wind measurements, which are crucial for localized severe weather events or in inaccessible regions such as over water and complex terrain.A novel ADL system – AIRflows (‘AIRborne fixed-beam lidar for wind measurements‘)  – has been developed by the Karlsruhe Institute of Technology (KIT) in collaboration with scientific and industrial partners during the last two years.Up to now, ADL systems use a single Doppler lidar attached to a scanner to provide radial velocity measurements under multiple viewing angles. Multiple viewing angles are needed to reconstruct the 3D wind from the unidirectional radial velocity measurements. Due to cost and size reductions of Doppler lidar units over the recent years, it has now become possible to construct an ADL system that uses multiple lidars with fixed-direction beams, instead of a single lidar with a scanning beam. The simultaneous availability of multiple viewing angles brings advantages: Simulation results have demonstrated that a multi-lidar system can achieve approximately one order of magnitude improved spatial wind measurement resolution as well as higher accuracy, compared to existing scanning systems.This contribution presents the novel AIRflows system developed by KIT. AIRflows implements the novel fixed-beam, multi-lidar concept onboard the TU Braunschweig Cessna F406 research aircraft. The system uses five modified Doppler lidar modules manufactured by Abacus Laser, one pointing nadir and the other four pointing forward, aft, left and right at an elevation of 30° from nadir.The first flights deploying AIRflows have been successfully completed during summer 2024. Initial analysis demonstrates wind profiles at 100 m spatial resolution, allowing to resolve fine-scale 3D winds inside the PBL for the first time. As part of the tests, flights to the Alps were conducted in preparation for the upcoming international TEAMx campaign. AIRflows measurements across Alpine valleys and crests provide previously unattainable insight into vertical wind and valley circulations in complex terrain. Similarly, AIRflows measurements across a wind farm in the North Sea provide novel vertically resolved insight into wind farm wake behavior.Overall, AIRflows revolutionizes the field of airborne wind measurements by providing an order of magnitude improved spatial resolution as well as higher measurement accuracy, compared to previously existing ADL.

The advantages of X-band polarimetric weather radar focus on its high spatio-temporal resolution and capability of multi-radar networking. However, the previously designed hydrometeor classification algorithm (HCA) for S-band weather radar is unsuitable for X-band weather radar due to the difference of backscattering characteristics and heavy precipitation attenuation. Therefore, the key technologies of hydrometeor classification algorithm and multi-radar mosaic algorithm for X-band polarimetric weather radar are proposed. First, it is found that the melting layer detection algorithm designed for S-band polarimetric weather radar is not suitable for X-band weather radar through analysis on the data collected by Beijing X-band radar network. A melting layer detection method based on quasi-vertical profile is proposed, which greatly improves the accuracy of obtaining the melting information. Second, a confidence threshold adjustment method is proposed to accurately estimate the data quality in the case of precipitation and clutter superposition. Third, an optimization method of membership functions based on data statistics is proposed to reconstruct the classification parameters suitable for Beijing X-band radar network. Finally, a multi-radar mosaic method based on rainfall attenuation is proposed, in which the reflectivity factors of networking radars are weighted and averaged by the data quality factor. Compared with the traditional method, it is found that the structural inhomogeneity of X-band radar mosaic result is effectively reduced. Those modifications effectively enhance the reliability of classification mosaic results of X-band weather radar network and provide technical support for the rapid deployment of X-band radar in China. Three typical precipitation cases in Beijing during the flood season in 2016 are used to compare the observational efficiency between X-band weather radar network and S-band operational radar. For the cases of convective rainfall, fine echo structures and reasonable hydrometeor distributions are found in X-band radar mosaic results. Especially for convective rainfall with short duration and small spatial scale, the advantage of X-band radar is more obvious, which alleviates the limited detection ability of S-band operational radar in urban areas. In addition, the hail falling area identified by X-band radar can be verified by manual observation in national weather stations. The performance of X-band weather radar network in large-scale stratiform precipitation, however, is not as good as S-band weather radar.

In order to improve the capacity of airports in view of the expected increasing amount of traffic the knowledge about the safety issues caused by wake vortices has to be improved. The final goal is to build up a wake vortex alert system to ensure the application of appropriate but not oversized safety distances in all weather conditions. Lidar systems are able to deliver very accurate data, but are also sensitive to the weather conditions like rain and fog. We did trials with the X-band radar BOR-A 550 on Orly Airport in November, 2006 at initial take-off and in October 2007 at ILS interception area. Continuous detection, characterization (strength : circulation), and profiling (age : young/mature/old/decaying) capabilities of wake vortices up to a range of 700 m have been proved in clear air and rainy weather. Opportunity detection of wake vortex was also obtained at long range until 7 Km in clear air. The Doppler resolution of around 0.2 m/s used with regularized high Doppler resolution techniques is able to characterize the wake vortex speed distribution in detail. X-band radar is a full-fledged alternative, which can make a significant contribution to a wake vortex alert system.

<p>Autonomous driving can be challenging especially in winter conditions when road surface is covered by icy and snow or visibility is low due to precipitation, fog or blowing snow. These harsh weather and road conditions set up very important requirements for the guidance systems of autonomous cars. In the normal conditions autonomous cars can drive without limitations but otherwise the speed must be reduced, and the safety distances increased to ensure safety on the roads. </p><p>Autonomous driving needs very precise and real-time weather and road condition information. Data can be collected from different sources, like (road) weather models, fixed road weather station network, weather radars and vehicle sensors (for example Lidars, radars and dashboard cameras). By combining the all relevant weather and road condition information a weather-based autonomous driving mode system is developed to help and guide autonomous driving. The driving mode system is dividing the driving conditions from perfect conditions to very poor conditions. In between there are several steps with slightly alternate driving modes depending for example snow intensity and friction. In the most challenging weather conditions, automatic driving must be stopped because the sensors guiding the driving are disturbed by for example heavy snowfall or icy road.</p><p>Finnish Meteorological Institute is testing autonomous driving in the Arctic vehicular test track in Sodankylä, Northern Finland. The test track is equipped with road weather observation system network including road weather stations, IoT sensors measuring air temperature and humidity along with various communication systems. Also, tailored road weather services are produced to the test track, like precise road weather model calculations and very accurate radar precipitation observations and nowcasting. The developed weather-based autonomous driving system is tested on Sodankylä test track among other arctic autonomous driving testing.</p><p>This study presents the Sodankylä Arctic vehicular test track environment and weather-based autonomous driving mode system that is developed at the Finnish Meteorological Institute.</p>

Nowadays, transmitting and receiving data with high speed and a high level of security are the main demands. So, a new model of spectral amplitude coding optical code division multiple access (SAC-OCDMA) is suggested in this paper, based on a free space optical (FSO) communication system using coherent sources. Three different codes: enhanced double weight (EDW), modified double weight (MDW) and multi-diagonal (MD) codes are assigned to our proposed model with the direct detection (DD) technique. Furthermore, the model is simulated under different weather conditions including clear air (CA), light mist (LM), very light fog, and light fog (LF). The system performance is evaluated through its bit error rate (BER), Q-factor, received power, and signal to noise ratio (SNR). Moreover, classification of the information received by the three different SAC-OCDMA using three different codes (EDW, MDW, and MD) is still challenging. So, two different machine learning (ML) algorithms are used, in this study, to classify the data received using the different codes. Detecting which code is received at the receiver end is important in order to reduce code error detection. Two algorithms: K-Nearest Neighbor (KNN) and Support Vector Machine (SVM) are adopted to classify different codes used for data transmission under four different weather conditions. The ML input dataset consists of the obtained simulation results, including Q-factor, BER, and SNR. Each feature is to be normalized before using ML. The obtained results show that the performance of the proposed FSO model achieved the longest propagation range under CA weather conditions, 7 km, while the shortest is under LF, which is 0.98 km. This is due to the attenuation of fog that causes signal degradation. The FSO system that uses EDW gives the best result under different weather conditions, while the system that uses MD code gives the worst performance. Also, the highest power is achieved when the EDW code is used at 5.5 km. The EDW has a received power of − 21.58 dBm, while the received power is − 22.04 dBm and − 23.8 dBm for MDW and MD codes, respectively. As for classification between the received information coming from three different codes under different weather conditions, both algorithms, KNN and SVM, achieve promising results in most cases. They showed more than 97% of classification accuracy under CA, LM, and LF weather conditions.

Abstract. In this study, we compare the wind measurements of a virtual tower triple Doppler lidar setup to those of a sonic anemometer located at a height of 90 m above ground on an instrumented tower and with those of two single Doppler lidars to evaluate the effect of the horizontal homogeneity assumption used for single Doppler lidar applications on the measurement accuracy. The triple lidar setup was operated in a 90 m stare and a step–stare mode at six heights between 90 and 500 m above ground, while the single lidars were operated in a continuous scan velocity–azimuth display (VAD) mode where one of them had a zenith angle of 54.7° and the other one of 28.0°. The instruments were set up at the boundary-layer field site of the German Meteorological Service (DWD) in July and August of 2020 during the FESST@MOL (Field Experiment on sub-mesoscale spatiotemporal variability at the Meteorological Observatory Lindenberg) 2020 campaign. Overall, we found good agreement of the lidar methods for the whole study period for different averaging times and scan modes compared to the sonic anemometer. For the step–stare mode wind speed measurements, the comparability between the triple lidar and the sonic anemometer was 0.47 m s−1 at an averaging time of 30 min with a bias value of −0.34 m s−1. For wind speed measured by one single lidar setup for the same period with an averaging time of 30 min, we found a comparability of 0.32 m s−1 at an averaging time of 30 min and a bias value of −0.07 m s−1 as well as values of 0.47 and −0.34 m s−1 for the other one, respectively. We also compared the wind velocity measurements of the single and triple lidars at different heights and found decreasing agreement between them with increasing measurement height up to 495 m above ground for the single lidar systems. We found that the single Doppler lidar with the increased zenith angle produced poorer agreement with the triple Doppler lidar setup than the one with the lower zenith angle, especially at higher altitudes. At a height of 495 m above ground and with an averaging time of 30 min the comparability and bias for the larger zenith angle were 0.71 and −0.50 m s−1, respectively, compared to values of 0.57 and −0.28 m s−1 for the smaller zenith angle. Our results confirm that a single Doppler lidar provides reliable wind speed and direction data over heterogeneous but basically flat terrain in different scan configurations. For the virtual tower scanning strategies, we developed a new filtering approach based on a median absolute deviation (MAD) filter combined with a relatively relaxed filtering criterion for the signal-to-noise ratio output by the instrument.

<p>Using data from cloud radar, ground observations and ERA5 reanalysis data, factors influencing nighttime precipitation during summer in the Yushu area of the Tibetan Plateau (TP) are investigated. The cloud top height (CTH), cloud base height (CBH) and liquid water content (LWC) are compared between the non-precipitating days and precipitating days. The results show that the average CTH during precipitating days over Yushu is below 10 km above ground level (hereafter AGL) in the daytime, while it is more than 10 km AGL at night with the maximum at 23 Beijing Standard Time (BST, = Coordinated Universal Time + 8 hour). The CBH is in phase with the dew-point spread. The precipitation intensity and CTH is in phase with the LWC. The hourly averaged precipitation intensity and convective available potential energy (CAPE) in ERA5 reach the maximum at 21 BST, which is 3 hours ahead of the observations. There is downward motion flow at noon during non-precipitating days, while there is upward motion flow at night during the precipitating days. In addition, the horizontal wind direction in the lower level (below 5000 m) shows clockwise rotation from morning to night. Wind shear occurs in the middle level of the atmosphere, is accompanied by subtropical westerly jet in the upper level. The difference of horizontal wind speed between the level of 200 hPa and 500 hPa is positively related to the LWC, making contribution to the formation of upper-level clouds</p>

Korea Institute of Civil Engineering and Building Technology (KICT) introduced X-band dual-polarization radar (KICT hydrological radar) in September 2013 to observe the heavy rainfall in urban area. It has been known that X-band dual-polarization radar is good for the observation of the heavy rainfall because the radar can provide data with high spatial-temporal resolution. This study estimated the radar rainfall by using the specific differential phase (KDP) from KICT hydrological radar and quantitatively assessed the radar rainfall. Forty two rain events were applied and eighty AWSs within the radar observational range were used for the assessment. As a result, there was no bias in the radar rainfall estimated by KDP. The accuracy of the radar rainfall was more than 50 % and the accuracy on the close range from 5 to 20 km was more than 60 %. Also, it has found that X-band dual-polarization radar was useful for the observation of the heavy rainfall than the small rainfall because the accuracy increased as the radar rainfall increase. Keywords: KICT Hydrolgocal Radar, X-band Dual-polarization Radar, Radar Rainfall, Heavy Rainfall

The FY-3G satellite, launched on 16 April 2023, represents a significant milestone in China, as it is the first satellite-based radar for precipitation monitoring in China and the third of its kind globally, following the TRMM and GPMCO satellites. The FY-3G is equipped with a precipitation measurement radar (PMR), capable of measuring precipitation at two different frequencies: 13.35 GHz (Ku-band) and 35.55 GHz (Ka-band). However, the capacity of satellites' precipitation radars is limited by the transmission power and frequency band, rendering precise rainfall measurement a persistent challenge for the international community. In this study, FY-3G's instantaneous rainfall products at Ku-band are quantitatively compared with the China New Generation Weather Radar (CINRAD) network. The weather radars used for this study are distributed across diverse terrains and regions, characterized by varied weather and climate conditions. To enhance the precision of the instantaneous rainfall product of the weather radar, real-time correction with a one-hour sliding time window is implemented between the weather radar and the ground-based automatic station one hour precipitation. Radar observations are matched by averaging data in common areas and re-sampling data to the satellite grid system for comparison on a point-to-point comparison. The analysis demonstrates that the FY-3G instantaneous rainfall products exhibit a strong correlation with weather radar, with a correlation coefficient of 0.73, and that the differences are consistent with a left skewed distribution with a 0 mm/h peak and a mean of -0.77 mm/h. The analysis also shows that the rain rate products have some false and missed data, with a probability of detection (POD) of 0.74 and a missing alarm rate (MAR) of 0.26 mainly concentrated in the weak precipitation. Although the observational capability of the FY-3G-PMR for light precipitation is slightly insufficient in the analysis cases, its overall performance is found to be satisfactory.

Investigations of high-density urban boundary layer under summer prevailing wind conditions with Doppler LiDAR: A case study in Hong Kong

Although hydrometeors attenuation is the most influential factor related to the total propagation losses on an Earth-space link at frequencies above 10 GHz, increasing rapidly at higher frequencies, several additional effects should not be ignored in the design of satellite communication systems. This paper analyzes the variability of fades time series in clear-air conditions both over the short-and the long-term. The study is based on experimental measurements from a Ka band beacon receiver. Simultaneous time series of various atmospheric parameters from measurement ancillary equipment like weather radar, ceilometer, ground meteorological stations, Meteosat products or radiosondes (RAOBS) are used for the performance of the study. The performance of the scintillation time series method currently recommended by ITU-R for the synthesis of the time series of propagation channel for Earth-space paths is checked against satellite beacon measurements.

Wind speed and direction, together with pressure, temperature, and relative humidity, are the most fundamental atmospheric state parameters. Accurate measurement of these parameters is crucial for numerical weather prediction. Vertically resolved wind measurements in the atmospheric boundary layer are particularly important for modeling pollutant and aerosol transport. The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility currently operates several scanning coherent Doppler lidar (DL) systems that provide accurate height-resolved measurements of wind speed and direction. These instruments operate in the near infrared (IR;1.5 microns) and provide range-resolved measurements of radial velocity, attenuated aerosol backscatter, and signal-to-noise ratio (SNR). The systems are operated using a fixed scan schedule consisting of plan position indicator (PPI) or Doppler Beam-Swing (DBS) scans. PPI scans are performed by scanning the beam in azimuth while maintaining a fixed elevation angle, and DBS scans are similar but typically also include a vertical beam. Radial velocity data from these scans are processed to yield profiles of wind speed direction. For stationary ground-based deployments, the Doppler Lidar Horizontal Wind Profiles (DLPROF-WIND) Value-Added-Product (VAP) provides height- and time-resolved measurements of the winds (Newsom and Krishnamurthy 2022). For operation on a moving platform, modifications to the existing DLPROF-WIND VAP are required to compensate for the effects of the platform motion. This report describes a parallel VAP, DLMCPROF-WIND, that was developed for computing motion-compensated wind profiles from ARM Doppler lidar data acquired during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign, when the lidar was deployed on the German icebreaker Polarstern.

A Doppler lidar by means of which remote measurements of the speed (in the range 0–55 m/sec) and direction of wind at specified heights (3–300 m) along with processing, representation, and transmission of the obtained data to an operator’s computer may be performed is created. The lidar is intended for off-line continuous operation in different weather conditions. Results of studies of its technical and metrological characteristics are presented.

Climate change and associated changes in weather patterns have globally widespread effects on natural systems. Shifts in phenology can affect the reproductive success of birds by causing a mismatch between the onset of breeding and favourable conditions for reproduction, such as a peak in food availability. Weather conditions and their changes have also long been discussed as affecting the reproductive success of grouse (Tetraoninae) and contributing to rapid declines in many central European populations. We monitored the reproductive success of Western Capercaillie Tetrao urogallus in the Black Forest, Germany, over a 14‐year period to study how weather conditions correlated to reproductive success and to assess whether changing environmental conditions were related to a seasonal shift in reproduction. We observed a temporal shift in peak lekking activity from late to mid‐April, which corresponds to an advance of 0.65 days/year. Furthermore, we show that warm conditions during the reproductive season were positively associated with reproductive success (i.e. larger brood size, more hens with chicks and more chicks per hen) and that precipitation volume during the early weeks after hatching was negatively correlated with brood size. Precipitation before copulation (i.e. peak of lekking) affected the proportion of hens with chicks and the number of chicks per hen. Sex ratio in broods was also affected by weather conditions, with more female than male chicks in years with low temperatures and high precipitation. By analysing spring weather predictions for the period 2020–2039, we found that weather conditions during the reproductive period remained constant when assuming a continued advancement of reproduction onset, although annual variation was high. We show the importance of weather conditions in influencing Western Capercaillie reproductive success. Western Capercaillie in the Black Forest seem to adjust the timing of reproduction according to changes in weather conditions, but this advancement is unlikely to be limitless, making the future impact of climate change on the species uncertain.

We present results from our recent development of a multi-beam Doppler lidar system for accurate 3-dimensional wind measurements. The eye-safe all-fibre system consists of a single seed laser that is amplified in multiple stages and shared between the three emitters. Steps towards wind turbine blade integration will be outlined.