Doppler Radar Fault Judgment System and Remote Monitoring Platform

The Doppler weather radar fault judging system and remote monitoring platform were introduced.Through the real-time scanning of radar alarm information coding,the platform can realize dynamic monitoring and real-time alarm of Doppler radar equipment components,so as to improve the reliability of equipment operation,and truly realize"unattended"remote monitoring.

Doppler Radar Data Analysis of A Low-shear Vortex System in Northern Guizhou

With Zunyi CINRAD/CD Doppler radar data and other data,a hail wind and heavy rainfall in short time occurred on July 10,2008 in northern Guizhou Province was analyzed in this study.The results showed that the system was affected by the southward of cold air pressure in a low-shear vortex zone.Echo monomer initially developed and arranged along the shear line,and there was hail weather in echo location with intense development.Before the hail shooting,the strongest echo value was 60-65 dBz.When the hail shooting,the low-elevation echo intensity sharply increased to 55-60 dBz with echo height of 11-15 km and VIL values>35 kg/m2,and its echo distribution showed band characteristics of vortex.When the vortex center moved to the original echo,echo intensity increased,resulting in a profound and lasting convergence of cyclones,and hail or strong wind occurred on the ground.Hail and strong short-term precipitation in towns of northern Renhuai might be related to the left inverted U-terrain.Echoes from Yongxing and Yuquan in Meitan,Xuekong and Xitou in Renhuai were the supercell echoes,and other regional hail shooting echoes were strong multi-monomer echoes.

Study on the method of polarization suppression of cheating jamming in pulse Doppler radar

A jamming suppression method based on polarization signal detection is proposed under common range and velocity cheating jammingfor pulse Doppler radar. On the basis of the separation of the target and the jamming, the range and velocity track on the true target are realized. Firstly the signal processing model of the full polarization pulse Doppler radar is introduced. Secondly the method of correct target separation is discussed, which is the twice detections of energy and polarization state on the two dimension resolution cells of range and velocity of the radar echo. Finally the simulations are performed and the results prove the validity. What's more, multiple range and velocity cheating jamming can be suppressed at the same time if the target and the jamming are different in the polarization domain.

Adaptive target and jamming recognition for the pulse doppler radar fuze based on a time-frequency joint feature and an online-updated naive bayesian classifier with minimal risk

This paper considers the problem of target and jamming recognition for the pulse Doppler radar fuze(PDRF).To solve the problem,the matched filter outputs of the PDRF under the action of target and jamming are analyzed.Then,the frequency entropy and peak-to-peak ratio are extracted from the matched filter output of the PDRF,and the time-frequency joint feature is constructed.Based on the time-frequency joint feature,the naive Bayesian classifier(NBC)with minimal risk is established for target and jamming recognition.To improve the adaptability of the proposed method in complex environments,an online update process that adaptively modifies the classifier in the duration of the work of the PDRF is proposed.The experiments show that the PDRF can maintain high recognition accuracy when the signal-to-noise ratio(SNR)decreases and the jamming-to-signal ratio(JSR)increases.Moreover,the applicable analysis shows that he ONBCMR method has low computational complexity and can fully meet the real-time requirements of PDRF.

The Characteristics Analysis of Typhoon "Meranti"(1010) and Discussion of Doppler Radar Location

Typhoon ' Meranti'(1010) is one of the rare offshore strengthened mini-typhoons,featured by heavy impacts,meandering moving route,small coverage,strong intensity and large difficulty in prediction and prevention.Therefore,the partial characteristics of such typhoon are analyzed in this paper and the discussions of location of the typhoon in offshore area by Doppler radar are the focus of this paper.

Doppler radar by using single multicarrier pulse based on optical fibre delay lines

The proposed Doppler measurement technique shows that the Doppler measurements can be accomplished by a single pulse with multiple frequency components through optical fibre delay lines.Range and velocity ambiguity can be removed,and the velocity resolution can be improved dramatically by using long optical fibre delay lines.Furthermore,the velocity resolution can be modified by adjusting the length of optical fibre delay lines.In addition,the proposed radar can achieve high range resolution by using a single wideband pulse.As a result,the new approach can improve radar performance significantly.

Convective Scale Structure and Evolution of a Squall Line Observed by C-Band Dual Doppler Radar in an Arid Region of Northwestern China

A long-lived and loosely organized squall line moved rapidly across U¨ru¨mqi, the capital city of Xinjiang Uygur Autonomous Region of China on 26 June 2005, generating hail and strong winds. The squall line was observed by a dual Doppler radar system in a field experiment conducted in 2004 and 2005 by the Chinese Academy of Meteorological Sciences and the local meteorological bureau in northwestern China. The 3D wind fields within the squall line were retrieved through dual Doppler analyses and a variational Doppler radar analysis system （VDRAS）. The formation and structure of the squall line as well as the genesis and evolution of embedded convective cells were investigated. During its life period, the squall line consisted of six storm cells extending about 100 km in length, and produced hail of about 25 mm in diameter and strong surface winds up to 11 m s^-1. Radar observations revealed a broad region of stratiform rain in a meso-β cyclone, with the squall line located to the west of this. Two meso-γ scale vortices were found within the squall line. Compared to typical squall lines in moist regions, such as Guangdong Province and Shanghai, which tend to be around 300–400 km in length, have echo tops of 17–19 km, and produce maximum surface winds of about 25 m s^-1 and temperature variations of about 8-C this squall line system had weaker maximum reflectivity （55 dBZ）, a lower echo top （13 km） and smaller extension （about 100 km）, relatively little stratiform rainfall preceding the convective line, and a similar moving speed and temperature variation at the surface.

Reliability of X-band Dual-polarization Phased Array Radars Through Comparison with an S-band Dual-polarization Doppler Radar

Based on the observations of a squall line on 11 May 2020 and stratiform precipitation on 6 June 2020 from two X-band dual-polarization phased array weather radars(DP-PAWRs)and an S-band dual-polarization Doppler weather radar(CINRAD/SA-D),the data reliability of DP-PAWR and its ability to detect the fine structures of mesoscale weather systems were assessed.After location matching,the observations of DP-PAWR and CINRAD/SA-D were compared in terms of reflectivity(Z_(H)),radial velocity(V),differential reflectivity(Z_(DR)),and specific differential phase(K_(DP)).The results showed that:(1)DP-PAWR has better ability to detect mesoscale weather systems than CINRAD/SAD;the multi-elevation-angles scanning of the RHI mode enables DP-PAWR to obtain a wider detection range in the vertical direction.(2)DP-PAWR’s Z_(H)and V structures are acceptable,while its sensitivity is worse than that of CINRAD/SA-D.The Z H suffers from attenuation and the Z_(H)area distribution is distorted around strong rainfall regions.(3)DP-PAWR’s Z_(DR)is close to a normal distribution but slightly smaller than that of CINRAD/SA-D.The K_(DP)products of DP-PAWR have much higher sensitivity,showing a better indication of precipitation.(4)DP-PAWR is capable of revealing a detailed and complete structure of the evolution of the whole storm and the characteristics of particle phase variations during the process of triggering and enhancement of a small cell in the front of a squall line,as well as the merging of the cell with the squall line,which cannot be observed by CINRAD/SA-D.With its fast volume scan feature and dual-polarization detection capability,DP-PAWR shows great potential in further understanding the development and evolution mechanisms of meso-γ-scale and microscale weather systems.

QUALITY CONTROL OF SINGLE DOPPLER RADAR DATA AND RETRIEVAL OF HORIZONTAL WIND FOR A LANDING TYPHOON

The removal of noise and velocity ambiguity and retrieval and verification of horizontal wind field is a prerequisite to make the best and fullest use of Doppler radar measurements. This approach was applied to the Doppler radar data collected during August 2005 for a landing typhoon Matsa (0509) in Yantai, Shangdong Province, and the verified result shows that the quality control for this dataset was successful. The horizontal wind field was retrieved and then verified by studying the characteristics of the radar radial velocity and large-scale wind field and the vertical cross section of the radial velocity determined with the typhoon center as the circle center and comparing it with satellite imagery. The results show that the meso- and small-scale systems in Matsa and its horizontal and vertical structure could be clearly retrieved using the dataset collected by single Doppler radar, and a shear or a convergence was corresponding with a band of severe storm around Matsa. At the same time, the retrieved wind field from single Doppler radar is proved to be a reliable and high-resolution dataset in analyzing the inner meso-scale structure of Matsa. It is also proved that the method for removing the velocity ambiguity could be an effective approach for preliminary quality control of the Doppler radar data, and the VAP method could also be a reasonable solution for the analysis of mesoscale wind field.

Kinematic Features of a Bow Echo in Southern China Observed with Doppler Radar

A bow echo is a type of mesoscale convective phenomenon that often induces extreme weather and appears with strong reflectivity on radar images. A strong bow echo that developed from a supercell was observed over Foshan City in southern China on 17 April 2011. The intense gusty winds and showers caused huge losses of property and severely affected human lives. This paper presents an analysis of this strong meso- n-scale convective system based on Doppler radar observations. The isolated bow echo exhibited a horizontal scale of about 80 km in terms of reflectivity above 40 dBZ, and a life span of 8 hours. The system originated from the merging of a couple of weakly organized cells in a shear line, and developed into an arch shape as it moved through the shear zone. Sufficient surface moisture supply ensured the convective instability and development of the bow echo. The low-altitude winds retrieved from single Doppler radar observations showed an obvious rear-inflow jet along the notch area. Different from the conventional definition, no book- end anticyclone was observed throughout the life cycle. Very strong slantwise updrafts and downdrafts were recognizable from the retrieved winds, even though the spatial scale of the bow echo was small. Strong winds and induced damage on the surface are considered to have been caused by the mid-level rear-inflow jet and intense convective downdrafts.

The Use of Dual-Doppler Radar Data in the Study of 1998 Meiyu Frontal Precipitationin Huaihe River Basin

During the Meiyu period in June and July of 1998, intensified field observations have been carried out for the project “Huaihe River Basin Energy and Water Cycle Experiment (HUBEX)”. For studying Meiyu front and its precipitation in Huaihe River basin, the present paper has performed analysis on the middle and lower level wind fields in the troposphere by using the radar data obtained from the two Doppler radars located at Fengtai district and Shouxian County. From June 29 to July 3 in 1998, the continuous heavy precipitation occurred in Huaihe River basin around Meiyu front. The precipitation process on July 2 occurred within the observation range of the two Doppler radar in Fengtai district and Shouxian County. The maximum rainfall of the Meiyu front was over 100 mm in 24 h, so it can be regarded as a typical mesoscale heavy precipitation process related to Meiyu front. Based on the wind field retrieved from the dual Doppler radar, we find that there are meso-γ scale vertical circulations in the vertical cross-section perpendicular to Meiyu front, the strong upward motion of which corresponds to the position of the heavy rainfall area. Furthermore, other results obtained by this study are identical with the results by analyzing the conventional synoptic data years ago. For example: in the vicinity of 3 km level height ahead of Meiyu front there exists a southwest low-level jet; the rainstorm caused by Meiyu front mainly occurs at the left side of the southwest low-level jet; and the Meiyu front causes the intensification of the low-level convergence in front of it. Key words Dual Doppler radar - Meiyu front - Meso—γ scale vertical circulation This research was supported by Project HUBEX (Project Number: 49794030) which is funded by the National Natural Science Foundation of China (NSFC).

Analysis of Doppler Radar Data of the Largest Snow Process since Winter

[Objective] Characteristics of Doppler radar data of the largest snow process since winter in Chengde City on February 26,2011 were discussed.[Method] By dint of reflection rate factors,radial velocity,and VWP product of Doppler radar in C wave in Chengde of Hebei Province,and coupled with large scale of circulation situation,the largest snow process since the winter in Chengde City on February 26,2011 was discussed.[Result] The echo intensity of snow was weak.If there was certain range of 30 dBz echo and was stable,there might be strong snow.The warm advection,convection and warm and wet air climbing over the thin cold cushion in the lower layer was the main reason of the precipitation.The structure of 'cattle eye' and the torrent in the lower air provided incessant water vapor for the generation of strong precipitation.When the wind in the vertical direction changed,there was wind speed divergence,which indicated that the precipitation weakened and stopped.The existence of warm advection and shear layer was the essential reason for the maintenance of precipitation.The 'ND' area in the middle layer and the northwest wind at any height indicated the end of precipitation.[Conclusion] The study provided theoretical basis for the forecast of strong snow.

Analysis of Doppler Radar Data about a Super Monomer Hailstorms in the Northeastern Qinghai-Tibet Plateau

[Objective] The Doppler radar data about a super monomer hailstorms in the northeastern Qinghai-Tibet Plateau in the Zhongchuan Airport in the Lanzhou City on September 6,2010 was studied.[Method] By dint of routine data and radar data,the low vortex shear line type and the super monomer hailstorm around the Zhongchuan Airport in the Lanzhou City on September 6,2010 were expounded.Basic product and secondary product of Doppler radar were used in this process to reflect the characteristics of strong convection weather.Some characteristics of this process shall be explored.[Result] A small gush of cold air from the cold vortex of 500 hPa in the middle and high layer provided impacts.The warm shear line provided water vapor and energy in the 700 hPa.There was strong convective weather in the upper air.Such 10 minutes of hailstorm was rarely seen in the drought land in the northwest.The characteristics of the strong convection were distinct and typical.The front showed no echo form.However,it can not be reflected in 'strong wedge' in another form.In this process,characteristics of BWER and middle scale cyclone were distinct.And this was a typical hailstorm process caused by super monomer.[Conclusion] The study provided some helpful references for the forecast of strong convection weather in the Zhongchuan Airport in Lanzhou City.

DOPPLER RADAR ECHO CHARACTERISTICS FOR COLD AIR INTRUDING INTO TYPHOON CHANCHU

With Doppler radar data from Shantou and Xiamen and the National Centers for Environmental Prediction and the National Center for Atmospheric Research （NCEP/NCAR） reanalysis data, the characteristics of a short-term heavy rainstorm on 17 May 2006 caused by Typhoon Chanchu are studied. Doppler radar data indicates that during the period from 1800 to 1900 May 17, the azimuthal phases of the positive and negative radial wind maximums are asymmetric around the core radius of the typhoon, i.e., the radial wind on the left side of the track is anomalously larger than that on the right side. Studies show that this is induced by the intrusion of cold air （northeasterly wind）, which is primarily located at the mid-lower layers, lower than 4 kin; this is due to the intruding cold air that forces the atmosphere to uplift, enhancing the release of instability energy, which triggers the heavy precipitation. During the late stage of the cold air activity, the typhoon is rapidly weakened. Consistent with the radar-observed intrusion of cold air, the NCEP/NCAR reanalysis of wind data also shows that there are obvious large scalar wind values at the mid-lower layers （approximately 1-3 km） to the left of the typhoon center （1800 May 17）, and in all regions--except those affected by the intruding cold air--the wind speeds on the right side of the track remain larger than those on the left side. Furthermore, the Rankine model results confirm that northeasterly cold air is introduced to the typhoon at the mid-lower layers to the left of the track. Calculations also point out that there exists a frontal zone with high θse that tilts from southeast to northwest with height and the super heavy rainstorm occurring in the south of Fujian province lies just near the fxontal zone.

The Characteristics of the Cold Front Cloud in Doppler Radar Reflectivity Factor

[Objective] The aim was to summarize the characteristics of refelectivity factors of Doppler radar of the cold front cloud system. [Method] Judging from the characteristics of reflectivity factors, by dint of the new generation weather radar in Harbin from 2002 to 2007, the features of the reflectivity factors of the cold front cloud system were summarized. [Result] The cloud formed by the cold front was in banded form in general. However, there was void in the cloud and its intensity was uneven. Most fast moving cold front was long and narrow banded echo and basically the radial velocity turned from northwest wind to southwest. With the changes of month, the feature of the reflective rate also changed. In winter, the cold front cloud was in layer form. The feature of the reflectivity factors was weak and in large area. However, the structure was loose and there was space in the echo. Among them, there were several strong echoes. Strong convection cell echo formed in the two sides of the cold front, and it moved with the entire cloud belt. When the dry cold front moved, regional strong convective current formed, mainly by convective cloud and small echo area. Generally, the changes of the wind direction can not be expounded from the radial velocity. However, the intensity of the convection cell was distinct, 'three-body scattering', 'side lobe echo', and 'weak echo', as well as features of super convection cell. [Conclusion] The study provided positive role for the application of Doppler radar in the surveillance of weather in Heilongjiang Province.

Doppler Radar Analysis on A Local Heavy Precipitation in Jieyang Area of Guangdong

By using Doppler weather radar data,the meso-scale characteristics of extremely heavy rainstorm process which happened suddenly in Jieyang urban area on July 31,2008 were analyzed.The results showed that the radar echo only needed 20 minutes from the generation to the strong echo which quickly strengthened above 50 dBz.The storm center went down south and went up north near Jieyang City all the time.The component which moved eastward was very tiny,and the heavy precipitation echo stagnated.In this heavy precipitation process,the characteristics types of radial velocity which were favorable to the generation and development of heavy precipitation echo appeared alternately each other.The radial velocity's characteristics types were the first type headwind zone,the second type headwind zone,meso-scale convergence type and cyclonic convergence and so on.Thus,this heavy precipitation process which broke the record happened.The analyses showed that the headwind zone which developed vigorously and the convergence which had influx and outflux airflow in the vertical direction of headwind zone made obvious contributions to the precipitation.

Research and Implementation of a Graphic System for Doppler Radar

Doppler radar have become one of the most important instruments for weather now casting,and for meso-scale weather research because of its higher spatial and temporal resolutions. A dealing system for Doppler radar graphic was researched and implemented so as to providing a convenient tool for users. We research and realized CINRAD/XD Doppler radar's graphic system. It contains three important parts:reading,standardization and pretreatment. It can be used very easily and conveniently. Besides,the system can be expanded and transplanted simply.

The WRF 3DVar System Combined with Physical Initialization for Assimilation of Doppler Radar Data

The three-dimensional variational data assimilation （3DVar） system of the Weather Research and Forecasting （WRF） model （WRF-Var） is further developed with a physical initialization （PI） procedure to assimilate Doppler radar radial velocity and reflectivity observations. In this updated 3DVar system, specific humidity, cloud water content, and vertical velocity are first derived from reflectivity with PI, then the model fields of specific humidity and cloud water content are replaced with the modified ones, and finally, the estimated vertical velocity is added to the cost-function of the existing WRF-Var （version 2.0） as a new observation type, and radial velocity observations are assimilated directly by the method afforded by WRF-Var. The new assimilation scheme is tested with a heavy convective precipitation event in the middle reaches of Yangtze River on 19 June 2002 and a Meiyu front torrential rain event in the Huaihe River Basin on 5 July 2003. Assimilation results show that the increments of analyzed variables correspond well with the horizontal distribution of the observed reflectivity. There are positive increments of cloud water content, specific humidity, and vertical velocity in echo region and negative increments of vertical velocity in echo-free region where the increments of horizontal winds present a clockwise transition. Results of forecast experiments show that the effects of adjusting cloud water content or vertical velocity directly with PI on forecast are not obvious. Adjusting specific humidity shows better performance in forecasting the precipitation than directly adjusting cloud water content or vertical velocity. Significant improvement in predicting precipitation as well as in reducing the model＇s spin-up time are achieved when radial velocity and reflectivity observations are assimilated with the new scheme.

ERROR COMPARISON OF WIND FIELD RETRIEVAL FROM SINGLE AND DUAL-DOPPLER RADAR OBSERVATIONS

The error distributions of the wind fields retrieved from single and dual-Doppler radar observations are given in this paper.The results indicate that the error of dual-Doppler retrieval depends on the position in the scan region of the dual-Doppler radar.The error of single-Doppler retrieval by using velocity azimuth processing(VAP)technique de- pends on the angle between the directions of wind and the radar beam.Generally,the winds retrieved from single Doppl- er radar are close to those retrieved from dual-Doppler radar.But,the error distribution of the single-Doppler retrieval is different from the dual-Doppler retrieval.We simulate the retrievals of single Doppler observation by the use of the output wind data from a 3-D numerical model of severe convection.The comparison of the simulated single-and dual-Doppler retrievals shows that the VAP may be a suitable technique for the operational analysis of mesoscale wind fields.It can also be used as a supplement to wind field retrieval in the field experiment.

Dynamical and Microphysical Retrieval from Simulated Doppler Radar Observations Using the 4DVAR Assimilation Technique

Based on a cloud model and the four-dimensional variational (4DVAR) dataassimilation method developed by Sun and Crook (1997), simulated experiments of dynamical andmicrophysical retrieval from Doppler radar data were performed. The 4DVAR data assimilationtechnique was applied to a cloud scale model with a warm rain parameterization scheme. The 3D wind,thermodynamical, and microphysieal fields were determined by minimizing a cost function, defined bythe difference between both radar observed radial velocities and reflectivities and their modelpredictions. The adjoint of the numerical model was used to provide the gradient of the costfunction with respect to the control variables. Experiments have demonstrated that the 4DVARassimilation method is able to retrieve the detailed structure of wind, thermodynamics, andmicrophysics by using either dual-Doppler or single-Doppler information. The quality of retrievaldepends strongly on the magnitude of constraint with respect to the variables. Retrieving thetemperature field, cloud water and water vapor is more difficult than the recovery of the wind fieldand rainwater. Accurate thermodynamic retrieval requires a longer assimilation period. Theinclusion of a background term, even mean fields from a single sounding, helped reduce the retrievalerrors. Less accurate velocity fields were obtained when single-Doppler data were used. It wasfound that the retrieved velocity is sensitive to the location of the retrieval domain relative tothe radars while the other fields have very little changes. Two radar volumetric scans are generallyadequate for providing the evolution, although the use of additional volumes improves theretrieval. As the amount of the observations decreases, the performance of the retrieval isdegraded. However, the missing observations can be compensated by adding a background term to thecost function. The technique is robust to random errors in radial velocity and calibration errors inreflectivity. The boundary conditions from the dual-Doppler synthesized winds are sufficient forthe retrieval. When the retrieval is mainly controlled by the observations in the regions away fromthe boundaries, the simple boundary conditions from velocity azimuth display (VAD) analysis are alsoavailable. The microphysical retrieval is sensitive to model errors.