Dual-polarization Radar Data Research Articles

Evaluation of X-Band Polarimetric-Radar Estimates of Drop-Size Distributions From Coincident S-Band Polarimetric Estimates and Measured Raindrop Spectra

Recent research has demonstrated the value of polarimetric measurements for the correction of rain-path attenuation at X-band radar frequency and the estimation of rain parameters including drop-size distributions (DSD). The issue this paper is concerned with is to what degree uncertainties in attenuation correction can affect the estimation of DSD. Since attenuation-correction uncertainty enhances with rain path, our hypothesis is that DSD retrieval uncertainty at X-band may deteriorate with range. In this paper, we evaluate the relative accuracy of X-band DSD retrieval against DSD estimates from S-band radar observations and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">situ</i> disdrometer spectra. We present comparisons of various techniques for estimating DSD model parameters from attenuation-corrected X-band dual-polarization radar data. Coincident X-band polarimetric-radar (XPOL) and S-band polarimetric-radar dual-polarized radar measurements from the International H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O Project experiment as well as coincident XPOL (MP-X) measurements over disdrometer during a typhoon storm case in Japan are used to assess the accuracy of the different DSD retrieval algorithms applied to X-band radar measurements.

A model for retrieval of dual linear polarization radar fields from model simulation outputs

An algorithm for retrieving polarimetric variables from numerical model fields is developed. By using this technique, radar reflectivity at horizontal polarization, differential reflectivity, specific differential phase shift and correlation coefficients between the horizontal and vertical polarization signals at zero lag can be derived from rain, snow and hail contents of numerical model outputs. Effects of environmental temperature and the melting process on polarimetric variables are considered in the algorithm. The algorithm is applied to the Advanced Regional Prediction System (ARPS) model simulation results for a hail storm. The spatial distributions of the derived parameters are reasonable when compared with observational knowledge. This work provides a forward model for assimilation of dual linear polarization radar data into a mesoscale model.

Structure and Maintenance Process of Stationary Double Snowbands along the Coastal Region

When a cold air outbreak occurred over the Sea of Japan, double snowbands stayed along the coastal region of the Kanazawa Plain from 15 to 16 January 2001: Snowband 1 on the seaward side, and Snowband 2 on the landward side. Their structures are studied mainly using Doppler and dual-polarization radars, and their maintenance processes are discussed. The double snowbands were maintained for about 20 hours. Snowband 1 had a stronger reflectivity and a higher echo top than Snowband 2. The cells in Snowband 2 were generated in the weak echo extending from Snowband 1 toward the land. Around the snowbands, a southeasterly land breeze, with a thickness of 400 m was present. A convergence between the land breeze and the northwesterly monsoon wind formed a strong updraft. Convective cells in Snowband 1 developed in association with the strong updraft. In Snowband 2, a weak convergence produced a weak updraft. The dual-polarization radar data showed that Snowband 1 was composed of spherical graupels, including conical ones. On the other hand, flat-shaped snow crystals were converted to snow aggregates along the trajectory of the particles within Snowband 2. Graupels were seen in the pictures taken below Snowband 1, while only snow aggregates were observed below Snowband 2. These facts indicate that the strong updraft at the land-breeze front contributed to the formation of graupels through the riming process in Snowband 1, on the other hand, snow aggregates developed through the deposition and aggregation processes in the weak updraft in Snowband 2. Some snow crystals, which contributed to the formation of snow aggregates in Snowband 2, were supplied from Snowband 1.

Drop Size Distributions Measured by a 2D Video Disdrometer: Comparison with Dual-Polarization Radar Data

An analysis of drop size distributions (DSDs) measured in four very different precipitation regimes is presented and is compared with polarimetric radar measurements. The DSDs are measured by a 2D video disdrometer, which is designed to measure drop size, shape, and fall speed with unprecedented accuracy. The observations indicate that significant DSD variability exists not only from one event to the next, but also within each system. Also, despite having vastly different storm structures and maximum rain rates, large raindrops with diameters greater than 5 mm occurred with each system. By comparing the occurrence of large drops with rainfall intensity, the authors find that the largest median diameters are not always associated with the heaviest rainfall, but are sometimes located either in advance of convective cores or, occasionally, in stratiform regions where rainfall rates are relatively low. Disdrometer and polarimetric radar measurements of radar reflectivity Z, differential reflectivity ZDR, specific differential phase KDP, and R(Z) and R(KDP) rain-rate estimators are compared in detail. Overall agreement is good, but it is found that both R(Z) and R(KDP) underestimate rain rate when the DSD is dominated by small drops and overestimate rain rate when the DSD is dominated by large drops. The results indicate that a classification of different rain types (associated with different DSDs) should be an essential part of polarimetric rainfall estimation. Furthermore, observations suggest that ZDR is a key parameter for making such a distinction. Last, the authors compute and compare maximum and average of gamma shape, slope, and intercept parameters for all four precipitation events. Potential measurement errors with the 2D video disdrometer are also discussed.

Operational Monitoring of Rainfall over the Arno River Basin Using Dual-Polarized Radar and Rain Gauges

Abstract Reflectivity (ZH) and differential reflectivity (ZDR) measurements collected by Polar 55C over the Arno River basin in Italy are presented. The applicability of dual-polarization (ZDR)-based rainfall algorithms at C band in an operational setting is studied in conjunction with a network of rain gauges. Conventional pointwise comparison of radar and rain gauge estimates of rainfall, as well as statistical comparison of dual-polarization radar and rain gauge data via probability matching procedure, are presented. Error structure of reflectivity rainfall Z-R relation, as well as ZDR-based algorithms, is evaluated as a function of spatial and temporal averaging. Pointwise comparison, as well as statistical evaluation based on cumulative distribution function (CDF) matching, are used to show that in an operational environment with excessive ground-clutter contamination and attenuation problems the dual-polarization-based rainfall algorithm performs better than any arbitrary Z-R relation. In addition, ...

Characteristics of the Vertical Profiles of Dual-Frequency, Dual-Polarization Radar Data in Stratiform Rain

Airborne dual-wavelength and dual-polarization radar data are analyzed for measurements taken in stratiform rain in the western Pacific during September 1990. The focus of the paper is on the vertical profiles of the linear depolarization ratio, LDR ( 10 GHz); the reflectivity factor, dBZ ( 10 GHz); and the dual-frequency ratio, DFR (10, 34.45 GHz). Statistical characterizations of the maxima of these quantities and the relative locations at which they occur suggest that the eccentricity of the melting particles is fairly large and that the shape and size of the particles are correlated. To try to explain these features, two types of simulation are presented. In the first, a set of measured drop size distributions is used in the context of a standard model of the melting layer. Variations in snow density, as well as shape, size, and orientation distributions are used to study the relationship between these parameters and the radar measurements. To reduce the amount of ambiguity in the estimation, a second type of simulation is described in which the size distribution of the snow is estimated. Comparisons between the simulated and measured profiles indicate that radar measurements can be used to derive certain characteristics of the particle size and shape distributions in the melting layer.

Satellite path diversity reception at 11.4 GHz: direct measurements, radar observations, and model predictions

Two-site diversity gain measurements made with a pair of 11.4 GHz satellite beacon receivers are compared to predictions based on dual-polarized radar reflectivity data and to values calculated from the Hodge model. All three agree closely. Examinations of data for a third path synthesized from radar data alone indicate that baseline orientation has a negligible effect on diversity gain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discrimination between hail and rain precipitation types from dual polarization radar, raingage and hailpad data

Dual polarization radar data (ZH andZDR) are analysed in 4 convective cells. Quite different relationships betweenZH andZDR are induced by the different hydrometer characteristics in these cells. The radar data, compiled with raingage and hailpad data obtained at the ground, show that in the mixed-phase (hail and rain) type of precipitations the differential reflectivityZDR is about 1.5 dB smaller than in the rain type of precipitations, without reaching zero values as in the hail type. In zones of strong precipitations the differential reflectivityZDR increase as the horizontal reflectivityZH, reaching values > 4 dB which indicate the existence of very big drops.

Application of edge detection techniques to detection of the bright band in radar data

An approach to the problem of automatically locating the melting layer is outlined. The approach uses image analysis techniques on dual and single polarization radar data.

Use of dual-polarization radar data for evaluation of attenuation on a satellite-to-earth path

Using conventional (single-polarization) radar data to assess attenuation due to rain on satellite-to-Earth paths requires the assumptions that the drops have a particular statistical distribution of sizes, and that the drops are of water. In the very localised regions of intense rain which influence such paths most severely, these assumptions can lead to large errors. This paper presents comparisons between direct measurements of attenuation and those computed using data from a dual-polarization radar technique. This technique can considerably reduce the errors of radar-derived estimates of attenuation. It also gives a clear distinction between ice and water.