scholarly journals Operational Monitoring of Radar Differential Reflectivity Using the Sun

2010 ◽  
Vol 27 (5) ◽  
pp. 881-887 ◽  
Author(s):  
Iwan Holleman ◽  
Asko Huuskonen ◽  
Rashpal Gill ◽  
Pierre Tabary
Keyword(s):  
The Sun ◽  
Volume Data ◽  
High Quality ◽  
Vertical Polarization ◽  
Monitoring Method ◽  
Daily Monitoring ◽  
Weather Radars ◽  
Radar Antenna ◽  
Differential Reflectivity ◽  
Receiver Bias

Abstract A method for the daily monitoring of the differential reflectivity bias for polarimetric weather radars is presented. Sun signals detected in polar volume data produced during operational scanning of the radar are used. This method is an extension of that for monitoring the weather radar antenna pointing at low elevations and the radar receiving chain using the sun. This “online” method is ideally suited for routine application in networks of operational radars. The online sun monitoring can be used to check the agreement between horizontal and vertical polarization lobes of the radar antenna, which is a prerequisite for high-quality polarimetric measurements. By performing both online sun monitoring and rain calibration at vertical incidence, the differential receiver bias and differential transmitter bias can be disentangled. Results from the polarimetric radars in Trappes (France) and Bornholm (Denmark), demonstrating the importance of regular monitoring of the differential reflectivity bias, are discussed. It is recommended that the online sun-monitoring method, preferably in combination with rain calibration, is routinely performed on all polarimetric weather radars because accurate calibration is a prerequisite for most polarimetric algorithms.

scholarly journals Improved analysis of solar signals for differential reflectivity monitoring

2016 ◽  
Author(s):  
Asko Huuskonen ◽  
Mikko Kurri ◽  
Iwan Holleman
Keyword(s):  
Vertical Polarization ◽  
Daily Monitoring ◽  
Weather Radars ◽  
Radar Network ◽  
Angle Data ◽  
Data Points ◽  
Reflectivity Data ◽  
Differential Reflectivity ◽  
Better Than ◽  
Receiver Bias

Abstract. The method for the daily monitoring of the differential reflectivity bias for polarimetric weather radars is developed. Improved quality control is applied to the solar signals detected during the operational scanning of the radar which removes efficiently rain and clutter contamination occurring in the solar hits. The simultaneous reflectivity data are used as a proxy to determine which data points are to be removed. A number of analysis methods are compared, and methods based on surface fitting are found superior to simple averaging. A separate fit to the reflectivity of the horizontal and vertical polarization channels is recommended, because it provides in addition to the differential reflectivity the pointing difference of the polarization channels, the squint angle. Data from the Finnish weather radar network shows that the squint angles are less than 0.02° and that the differential reflectivity bias is stable and determined to better than 0.04 dB. The results are compared to those from measurements at vertical incidence, which allows to determine the differential receiver bias and the transmitter bias.

scholarly journals Improved analysis of solar signals for differential reflectivity monitoring

2016 ◽  
Vol 9 (7) ◽  
pp. 3183-3192 ◽  
Author(s):  
Asko Huuskonen ◽  
Mikko Kurri ◽  
Iwan Holleman
Keyword(s):  
Vertical Polarization ◽  
Daily Monitoring ◽  
Weather Radars ◽  
Radar Network ◽  
Total Differential ◽  
Data Points ◽  
Reflectivity Data ◽  
Differential Reflectivity ◽  
Better Than ◽  
Receiver Bias

Abstract. The method for the daily monitoring of the differential reflectivity bias for polarimetric weather radars is developed further. Improved quality control is applied to the solar signals detected during the operational scanning of the radar, which efficiently removes rain and clutter-contaminated gates occurring in the solar hits. The simultaneous reflectivity data are used as a proxy to determine which data points are to be removed. A number of analysis methods to determine the differential reflectivity bias are compared, and methods based on surface fitting are found superior to simple averaging. A separate fit to the reflectivity of the horizontal and vertical polarization channels is recommended because of stability. Separate fitting also provides, in addition to the differential reflectivity bias, the pointing difference of the polarization channels. Data from the Finnish weather radar network show that the pointing difference is less than 0.02° and that the differential reflectivity bias is stable and determined to better than 0.04 dB. The results are compared to those from measurements at vertical incidence, which allows us to determine the total differential reflectivity bias including the differential receiver bias and the transmitter bias.

Operational Monitoring of Weather Radar Receiving Chain Using the Sun

2010 ◽  
Vol 27 (1) ◽  
pp. 159-166 ◽  
Author(s):  
Iwan Holleman ◽  
Asko Huuskonen ◽  
Mikko Kurri ◽  
Hans Beekhuis
Keyword(s):  
Weather Radar ◽  
Radar Data ◽  
The Sun ◽  
Volume Data ◽  
Operational Monitoring ◽  
Flux Data ◽  
Weather Radars ◽  
Receiver System ◽  
The Stability ◽  
Radar Antenna

Abstract A method for operational monitoring of a weather radar receiving chain, including the antenna gain and the receiver, is presented. The “online” method is entirely based on the analysis of sun signals in the polar volume data produced during operational scanning of weather radars. The method is an extension of that for determining the weather radar antenna pointing at low elevations using sun signals, and it is suited for routine application. The solar flux from the online method agrees very well with that obtained from “offline” sun tracking experiments at two weather radar sites. Furthermore, the retrieved sun flux is compared with data from the Dominion Radio Astrophysical Observatory (DRAO) in Canada. Small biases in the sun flux data from the Dutch and Finnish radars (between −0.93 and +0.47 dB) are found. The low standard deviations of these sun flux data against those from DRAO (0.14–0.20 dB) demonstrate the stability of the weather radar receiving chains and of the sun-based online monitoring. Results from a daily analysis of the sun signals in online radar data can be used for monitoring the alignment of the radar antenna and the stability of the radar receiver system. By comparison with the observations from a sun flux monitoring station, even the calibration of the receiving chain can be checked. The method presented in this paper has great potential for routine monitoring of weather radars in national and international networks.

scholarly journals A sun-tracking method to improve the pointing accuracy of weather radar

2011 ◽  
Vol 4 (4) ◽  
pp. 5569-5595
Author(s):  
X. Muth ◽  
M. Schneebeli ◽  
A. Berne
Keyword(s):  
Weather Radar ◽  
Radar Data ◽  
Swiss Alps ◽  
The Sun ◽  
Sources Of Information ◽  
Weather Radars ◽  
Pointing Accuracy ◽  
Instrumental Bias ◽  
Radar Antenna ◽  
Land Cover Maps

Abstract. Accurate positioning of data collected by a weather radar is of primary importance for their appropriate georeferencing, which in turn makes it possible to combine those with additional sources of information (topography, land cover maps, meteorological simulations from numerical weather models to list a few). This issue is especially acute for mobile radar systems, for which accurate and stable levelling might be difficult to ensure. The sun is a source of microwave radiation, which can be detected by weather radars and used for the accurate positioning of the radar data. This paper presents a technique based on the sun echoes to quantify and hence correct for the instrumental errors which can affect the pointing accuracy of radar antenna. The proposed method is applied to data collected in the Swiss Alps using a mobile X-band radar system. The obtained instrumental bias values are evaluated by comparing the locations of the ground echoes predicted using these bias estimates with the observed ground echo locations. The very good agreement between the two confirms the good accuracy of the proposed method.

scholarly journals Solar Monitoring of the NEXRAD WSR-88D Network using Operational Scan Data

2021 ◽  
Keyword(s):  
Observation Time ◽  
Noise Power ◽  
Monitoring Method ◽  
Continental Scale ◽  
Weather Radars ◽  
Routine Monitoring ◽  
Geographical Maps ◽  
Scan Data ◽  
One Year ◽  
Differential Reflectivity

Abstract Solar monitoring is a method in which solar interferences, recorded during operational scanning of a radar, are used to monitor antenna pointing, identify signal processor issues, track receiver chain stability, and check the balance between horizontal and vertical polarization receive channels. The method is used by Eumetnet to monitor more than 100 radars in twenty European countries and it has been adopted by many national weather services across the world. NEXRAD is a network of 160 similar S-band weather radars (WSR-88Ds), which makes it most suitable for assessing the capability of the solar monitoring method on a continental scale. The NEXRAD Level-II data contain radial-by-radial noise power estimates. An increase in this estimate is observed when the antenna points close to the sun. Our decoding software extracts these noise power estimates for the horizontal and vertical receive channels (converted to solar flux units) and other relevant metadata, including azimuth, elevation, observation time and radar location. Here we present results of analyzing one year of solar-monitoring data generated by 142 radars from the contiguous United States. We show monitoring results, geographical maps, and statistical outcomes on antenna pointing, solar fluxes, and differential reflectivity biases. We also assess the quality of the radars by defining a Figure of Merit, which is calculated from the solar monitoring results. The results demonstrate that the solar method provides great benefit for routine monitoring and harmonization of national and transnational operational radar networks.

scholarly journals Rapid High Quality Compression of Volume Data for Visualization

2001 ◽  
Vol 20 (3) ◽  
pp. 49-57 ◽  
Author(s):  
Ky Giang Nguyen ◽  
Dietmar Saupe
Keyword(s):  
Volume Data ◽  
High Quality

scholarly journals Oscillations in the Sun with SONG: Setting the scale for asteroseismic investigations

2019 ◽  
Vol 623 ◽  
pp. L9 ◽  
Author(s):  
M. Fredslund Andersen ◽  
P. Pallé ◽  
J. Jessen-Hansen ◽  
K. Wang ◽  
F. Grundahl ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Quality Data ◽  
Scaling Relations ◽  
The Sun ◽  
Average Amplitude ◽  
Echelle Spectrograph ◽  
High Quality ◽  
Data Set ◽  
High Quality Data ◽  
High Cadence

Context. We present the first high-cadence multiwavelength radial-velocity observations of the Sun-as-a-star, carried out during 57 consecutive days using the stellar échelle spectrograph at the Hertzsprung SONG Telescope operating at the Teide Observatory. Aims. Our aim was to produce a high-quality data set and reference values for the global helioseismic parameters νmax, ⊙ and Δν⊙ of the solar p-modes using the SONG instrument. The obtained data set or the inferred values should then be used when the scaling relations are applied to other stars showing solar-like oscillations observed with SONG or similar instruments. Methods. We used different approaches to analyse the power spectrum of the time series to determine νmax, ⊙: simple Gaussian fitting and heavy smoothing of the power spectrum. We determined Δν⊙ using the method of autocorrelation of the power spectrum. The amplitude per radial mode was determined using the method described in Kjeldsen et al. (2008, ApJ, 682, 1370). Results. We found the following values for the solar oscillations using the SONG spectrograph: νmax, ⊙ = 3141 ± 12 μHz, Δν⊙ = 134.98 ± 0.04 μHz, and an average amplitude of the strongest radial modes of 16.6 ± 0.4 cm s−1. These values are consistent with previous measurements with other techniques.

scholarly journals Observational and Modeling Study of Ice Hydrometeor Radar Dual-Wavelength Ratios

2019 ◽  
Vol 58 (9) ◽  
pp. 2005-2017 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Maximilian Maahn ◽  
Gijs de Boer
Keyword(s):  
Rayleigh Scattering ◽  
Elevation Angle ◽  
Characteristic Size ◽  
Dual Wavelength ◽  
Spherical Particles ◽  
Nonspherical Particles ◽  
Dual Frequency ◽  
Weather Radars ◽  
W Band ◽  
Differential Reflectivity

AbstractThe influence of ice hydrometeor shape on the dual-wavelength ratio (DWR) of radar reflectivities at millimeter-wavelength frequencies is studied theoretically and on the basis of observations. Data from dual-frequency (Ka–W bands) radar show that, for vertically pointing measurements, DWR increasing trends with reflectivity Ze are very pronounced when Ka-band Ze is greater than about 0 dBZ and that DWR and Ze values are usually well correlated. This correlation is explained by strong relations between hydrometeor characteristic size and both of these radar variables. The observed DWR variability for a given level of reflectivity is as large as 8 dB, which is in part due to changes in mean hydrometeor shape as expressed in terms of the particle aspect ratio. Hydrometeors with a higher degree of nonsphericity exhibit lower DWR values when compared with quasi-spherical particles because of near-zenith reflectivity enhancements for particles outside the Rayleigh-scattering regime. When particle mass–size relations do not change significantly (e.g., for low-rime conditions), DWR can be used to differentiate between quasi-spherical and highly nonspherical hydrometeors because (for a given reflectivity value) DWR tends to increase as particles become more spherical. Another approach for differentiating among different degrees of nonsphericity for larger scatterers is based on analyzing DWR changes as a function of radar elevation angle. These changes are more pronounced for highly nonspherical particles and can exceed 10 dB. Measurements of snowfall spatiotemporally collocated with spaceborne CloudSat W-band radar and ground-based S-band operational weather radars also indicate that DWR values are generally smaller for ice hydrometeors with higher degrees of nonsphericity, which, for the same level of S-band reflectivity, exhibit greater differential reflectivity values.

scholarly journals Characteristics of the Bright Band Based on Quasi-Vertical Profiles of Polarimetric Observations from an S-Band Weather Radar Network

2020 ◽  
Vol 12 (24) ◽  
pp. 4061
Author(s):  
Jeong-Eun Lee ◽  
Sung-Hwa Jung ◽  
Soohyun Kwon
Keyword(s):  
Signal To Noise Ratio ◽  
Vertical Profiles ◽  
Bright Band ◽  
Weather Radars ◽  
Radar Network ◽  
Temperature Zero ◽  
The Mean ◽  
Microphysical Processes ◽  
Differential Reflectivity ◽  
Self Consistency

Bright band (BB) characteristics obtained via dual-polarization weather radars elucidate thermodynamic and microphysical processes within precipitation systems. This study identified BB using morphological features from quasi-vertical profiles (QVPs) of polarimetric observations, and their geometric, thermodynamic, and polarimetric characteristics were statistically examined using nine operational S-band weather radars in South Korea. For comparable analysis among weather radars in the network, the calibration biases in reflectivity (ZH) and differential reflectivity (ZDR) were corrected based on self-consistency. The cross-correlation coefficient (ρHV) bias in the weak echo regions was corrected using the signal-to-noise ratio (SNR). First, we analyzed the heights of BBPEAK derived from the ZH as a function of season and compared the heights of BBPEAK derived from the ZH, ZDR, and ρHV. The heights of BBPEAK were highest in the summer season when the surface temperature was high. However, they showed distinct differences depending on the location (e.g., latitude) within the radar network, even in the same season. The height where the size of melting particles was at a maximum (BBPEAK from the ZH) was above that where the oblateness of these particles maximized (BBPEAK from ZDR). The height at which the inhomogeneity of hydometeors was at maximum (BBPEAK from the ρHV) was also below that of BBPEAK from the ZH. Second, BB thickness and relative position of BBPEAK were investigated to characterize the geometric structure of the BBs. The BB thickness increased as the ZH at BBBOTTOM increased, which indicated that large snowflakes melt more slowly than small snowflakes. The geometrical structure of the BBs was asymmetric, since the melting particles spent more time forming the thin shell of meltwater around them, and they rapidly collapsed to form a raindrop at the final stage of melting. Third, the heights of BBTOP, BBPEAK, and BBBOTTOM were compared with the zero-isotherm heights. The dry-temperature zero-isotherm heights were between BBTOP and BBBOTTOM, while the wet-bulb temperature zero-isotherm heights were close to the height of BBPEAK. Finally, we examined the polarimetric observations to understand the involved microphysical processes. The correlation among ZH at BBTOP, BBPEAK, and BBBOTTOM was high (>0.94), and the ZDR at BBBOTTOM was high when the BB’s intensity was strong. This proved that the size and concentration of snowflakes above the BB influence the size and concentration of raindrops below the BB. There was no depression in the ρHV for a weak BB. Finally, the mean profile of the ZH and ZDR depended on the ZH at BBBOTTOM. In conclusion, the growth process of snowflakes above the BB controls polarimetric observations of BB.

scholarly journals Differential Reflectivity Calibration and Antenna Temperature

2017 ◽  
Vol 34 (9) ◽  
pp. 1885-1906 ◽  
Author(s):  
J. C. Hubbert
Keyword(s):  
Thermal Expansion ◽  
Doppler Radar ◽  
Radar Data ◽  
The Sun ◽  
Dual Polarization ◽  
Calibration Technique ◽  
Atmospheric Research ◽  
Using Data ◽  
Power Measurements ◽  
Differential Reflectivity

AbstractTemporal differential reflectivity bias variations are investigated using the National Center for Atmospheric Research (NCAR) S-band dual-polarization Doppler radar (S-Pol). Using data from the Multi-Angle Snowflake Camera-Ready (MASCRAD) Experiment, S-Pol measurements over extended periods reveal a significant correlation between the ambient temperature at the radar site and the bias. Using radar scans of the sun and the ratio of cross-polar powers, the components of the radar that cause the variation of the bias are identified. It is postulated that the thermal expansion of the antenna is likely the primary cause of the observed bias variation. The cross-polar power (CP) calibration technique, which is based on the solar and cross-polar power measurements, is applied to data from the Plains Elevated Convection at Night (PECAN) field project. The bias from the CP technique is compared to vertical-pointing bias measurements, and the uncertainty of the bias estimates is given. An algorithm is derived to correct the radar data for the time- and temperature-varying bias. Bragg scatter measurements are used to corroborate the CP technique bias measurements.

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