Showing papers on "Weather radar published in 2001"

The Use of TRMM Precipitation Radar Observations in Determining Ground Radar Calibration Biases

Abstract: Since the successful launch of the Tropical Rainfall Measuring Mission (TRMM) satellite, measurements of a wide variety of precipitating systems have been obtained with unprecedented detail from the first space-based radar [precipitation radar (PR)]. In this research, a methodology is developed that matches coincident PR and ground-based volume scanning weather radar observations in a common earth parallel three-dimensional Cartesian grid. The data matching is performed in a way that minimizes uncertainties associated with the type of weather seen by the radars, grid resolution, and differences in radar sensitivities, sampling volumes, viewing angles, and radar frequencies. The authors present comparisons of reflectivity observations from the PR and several U.S. weather surveillance Doppler radars (WSR-88D) as well as research radars from the TRMM field campaigns in Kwajalein Atoll and the Large Biosphere Atmospheric (LBA) Experiment. Correlation values above 0.8 are determined between PR and ground radar matched data for levels above the zero isotherm. The reflectivity difference statistics derived from the matched data reveal radar systems with systematic differences ranging from 1 2t o27 dB. The authors argue that the main candidate for systematic differences exceeding 1 to 1.5 dB is the ground radar system calibration bias. To verify this argument, the authors used PR comparisons against well-calibrated ground-based systems, which showed systematic differences consistently less than 1.5 dB. Temporal analysis of the PR versus ground radar systematic differences reveals radar sites with up to 4.5dB bias changes within periods of two to six months. Similar evaluation of the PR systematic difference against stable ground radar systems shows bias fluctuations of less than 0.8 dB. It is also shown that bias adjustment derived from the methodology can have significant impact on the hydrologic applications of ground-based radar measurements. The proposed scheme can be a useful tool for the systematic monitoring of ground radar biases and the studying of its effect.

Space-time calibration of radar rainfall data

Abstract: Motivated by a specific problem concerning the relationship between radar reflectance and rainfall intensity, the paper develops a space–time model for use in environmental monitoring applications. The model is cast as a high dimensional multivariate state space time series model, in which the cross-covariance structure is derived from the spatial context of the component series, in such a way that its interpretation is essentially independent of the particular set of spatial locations at which the data are recorded. We develop algorithms for estimating the parameters of the model by maximum likelihood, and for making spatial predictions of the radar calibration parameters by using realtime computations. We apply the model to data from a weather radar station in Lancashire, England, and demonstrate through empirical validation the predictive performance of the model.

Comparisons of Rain Rate and Reflectivity Factor Derived from the TRMM Precipitation Radar and the WSR-88D over the Melbourne, Florida, Site

Abstract: Validating the results from the spaceborne Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) requires comparisons with well-calibrated ground-based radar measurements. At altitudes near the storm top, where effects of PR signal attenuation are small, the data are used to check the relative calibration accuracy of the radars. Near the surface, where attenuation effects at the PR frequency of 13.8 GHz can be significant, the data provide an assessment of the performance of the PR attenuation correction algorithm. The ground-based data are taken from the Doppler Weather Surveillance (WSR-88D) radar located at Melbourne, Florida. In 1998, 24 overpasses of the TRMM satellite over the Melbourne site occurred during times when significant precipitation was present in the overlap region of the PR and WSR-88D. Resampling the ground-based and spaceborne datasets to a common grid provides a means by which the radar reflectivity factors (dBZ) can be compared at different heights and for dif...

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

Abstract: 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 ...

Weather Support to Deicing Decision Making (WSDDM) : A winter weather nowcasting system

Abstract: This paper describes a winter weather nowcasting system called Weather Support to Deicing Decision Making (WSDDM), designed to provide airline, airport, and air traffic users with winter weather information relevant to their operations. The information is provided on an easy to use graphical display and characterizes airport icing conditions for nonmeteorologists. The system has been developed and refined over a series of winter–long airport demonstrations at Denver's Stapleton International Airport, Chicago's O'Hare International Airport, and New York's LaGuardia Airport. The WSDDM system utilizes commercially available weather information in the form of Next Generation Weather Radar WSR–88D radar reflectivity data depicted as color coded images on a window of the display and Aviation Routine Weather Report (METAR) surface weather reports from Automated Surface Observating System stations and observers. METAR information includes wind speed and direction, air temperature, and precipitation type/...

Image processing for hazard recognition in on-board weather radar

Abstract: A method of providing weather radar images to a user includes obtaining radar image data corresponding to a weather radar image to be displayed. The radar image data is image processed to identify a feature of the weather radar image which is potentially indicative of a hazardous weather condition. The weather radar image is displayed to the user along with a notification of the existence of the feature which is potentially indicative of the hazardous weather condition. Notification can take the form of textual information regarding the feature, including feature type and proximity information. Notification can also take the form of visually highlighting the feature, for example by forming a visual border around the feature. Other forms of notification can also be used.

Simultaneous observations of rain cells over the ocean by the synthetic aperture radar aboard the ERS satellites and by surface‐based weather radars

Abstract: Radar images acquired over the ocean by the C band synthetic aperture radar (SAR) aboard the European Remote Sensing satellites ERS 1 and ERS 2 often show sea surface manifestations of rain cells. We have searched the archives of several weather stations for weather radar data acquired concurrently with ERS SAR data and have found four concurrent data pairs: one in the South China Sea, two in the Baltic Sea and one in the North Sea. The comparison of ERS 1/2 SAR images showing radar signatures of rain cells with weather radar images reveals that the radar signatures of rain cells on ERS SAR images vary considerably, which makes it often difficult to distinguish them from radar signatures of other mesoscale or submesoscale atmospheric and oceanic phenomena. The present analysis, together with results obtained from previous analyses of spaceborne multifrequency SAR data and laboratory data as well as results obtained from theoretical models on radar backscattering at the sea surface suggest the following: C band radar signatures of rain cells with rain rates below 50 mm/h are mainly caused by a modification of the sea surface roughness induced by (1) the raindrops impinging on the sea surface and thus modifying the sea surface roughness and by (2) local wind field variations associated with rain cells (spreading downdrafts). Raindrops impinging on the sea surface generate ring waves as well as turbulence in the upper water layer. Depending on rain rate, drop size distribution, wind speed, and temporal evolution of the rain event, the net effect can be an increase or a reduction of the amplitude of the C band Bragg waves and thus of the backscattered radar power. Thus ocean areas struck by rain can show up on ERS SAR images as areas with higher or lower image brightness than the surroundings.

Validation of the Rain Profiling Algorithm “ZPHI” from the C-Band Polarimetric Weather Radar in Darwin

Abstract: An extensive application of a rain profiling algorithm (ZPHI) employing a C-band polarimetric radar (the C-POL radar of the Australian Bureau of Meteorology Research Centre in Darwin) is presented. ZPHI belongs to the class of rain profiling algorithms that have been developed for spaceborne or airborne radars operating at attenuating frequencies. By nature, these algorithms are nonlocal: the full profile of the measured radar reflectivity is inverted to derive a retrieved profile of the rainfall rate. The retrieval accuracy lays in the imposition of an “external constraint” in the inversion procedure. In this case, that is supplied by the differential phase shift ΦDP. The primary products of ZPHI are the profile along the beam of the specific attenuation A, and the “normalized” intercept parameter N*0. The rainfall rate is further estimated through an R–A relation adjusted for N*0. ZPHI solves automatically two problems met when operating at C band: the along-path attenuation and the variability...

High accuracy, high integrity scene mapped navigation

Abstract: An aircraft including an approach and landing system, including a navigation unit for providing navigation information, a weather radar unit for providing radar information, a processor which receives navigation information from the navigation unit and information from the weather radar unit, the processor unit providing an output representing information concerning the aircraft in accordance with the provided navigation information and radar information, a memory for storing information representing a scene, the processor unit correlating the stored scene information with the output representing information concerning the aircraft to provide a mapped scene, a display unit for displaying the output of said processor and the mapped scene, and a steppable frequency oscillator for providing a signal which is stepped in frequency to the weather radar unit, thereby providing an increased range resolution.

Hydrological Forecasting and Real Time Monitoring in Finland: The Watershed Simulation and Forecasting System (WSFS)

Abstract: simulation and forecasting system is widely used in Finland for simulation of hydrological cycle and for making real-time forecasts. The system is based on a watershed model. This was based originally on the HBV-model and simulates the hydrological cycle using standard meteorological data. The model simulates the whole land area of Finland, including cross-border watersheds. This is a total of 390,000 km 2 . The model simulates the area at a sub- basin level. The area is divided into 6,200 sub-basins. The inputs for the model are precipitation and temperature and the simulated components of hydrological cycle are snow accumulation and melt, soil moisture, evaporation, ground water, runoff and discharges and water levels of main rivers and lakes. The input temperature and precipitation comes from 54 real time temperature observation stations, 179 precipitation observation stations and from the weather radar network, which covers almost all Finland. The data assimilation algorithm of the model updates the simulation by assimilating real time water level and discharge observations from 487 stations together with snow water equivalent observations from 158 stations and satellite data of snow cover area and flood cover area. The model uses ensemble weather forecast from the European Centre for Medium Range weather Forecasting (ECMWF). The hydrological forecast is made by simulating the model with 42 different 10 day weather forecasts after which historical weather data is used to make a hydrological forecast for one year. Out of the 42 hydrological forecasts a mean forecast is selected and together with mean forecast the uncertainty limits of the forecast is shown. Hydrological forecasts for over 1300 rivers and lakes are updated several times a day and provided for the users via public internet pages at www.environment.fi/waterforecast. In the case of serious flood an automatic email warning is sent to flood protection officers.

Efficient estimation of spectral moments and the polarimetric variables on weather radars, sonars, sodars, acoustic flow meters, lidars, and similar active remote sensing instruments

Abstract: A method for estimation of Doppler spectrum, its moments, and polarimetric variables on pulsed weather radars which uses over sampled echo components at a rate several times larger than the reciprocal of transmitted pulse length. The variables are estimated by suitably combining weighted averages of the over sampled signals in range with usual processing of samples at a fixed range location. The invention may be Used on pulsed weather radar, lidars, sonars and accoustic flow meters.

Statistical Methods of Estimating Average Rainfall over Large Space–Timescales Using Data from the TRMM Precipitation Radar

Abstract: Data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar represent the first global rain-rate dataset acquired by a spaceborne weather radar. Because the radar operates at an attenuating wavelength, one of the principal issues concerns the accuracy of the attenuation correction algorithms. One way to test these algorithms is by means of a statistical method in which the probability distribution of rain rates at the high end is inferred by measurements at the low to intermediate range and by the assumption that the rain rates are lognormally distributed. Investigation of this method and the area–time integral methods using a global dataset provides an indication of how well methods of this kind can be expected to perform over different space–timescales and climatological regions using the sparsely sampled TRMM radar data. Identification of statistical relationships among the rain parameters and an understanding of the rain-rate distribution as a function of time and space may h...

Retrieval of Atmospheric Attenuation Using Combined Ground-Based and Airborne 95-GHz Cloud Radar Measurements

Abstract: Cloud measurements at millimeter-wave frequencies are affected by attenuation due to atmospheric gases, clouds, and precipitation Estimation of the true equivalent radar reflectivity, Ze, is complicated because extinction mechanisms are not well characterized at these short wavelengths This paper discusses cloud radar calibration and intercomparison of airborne and ground-based radar measurements and presents a unique algorithm for attenuation retrieval This algorithm is based on dual 95-GHz radar measurements of the same cloud and precipitation volumes collected from opposing viewing angles True radar reflectivity is retrieved by combining upward-looking and downward-looking radar profiles This method reduces the uncertainty in radar reflectivity and attenuation estimates, since it does not require a priori knowledge of hydrometeors’ microphysical properties Results from this technique are compared with results retrieved from the Hitschfeld and Bordan algorithm, which uses single-radar measurements with path-integrated attenuation as a constraint Further analysis is planned to employ this dual-radar algorithm in order to refine single-radar attenuation retrieval techniques, which will be used by operational sensors such as the CloudSat radar

An ERS-1 synthetic aperture radar image of a tropical squall line compared with weather radar data

Abstract: A radar image acquired by the C-band synthetic aperture radar (SAR) aboard the European Remote Sensing satellite ERS-2 over the coastal waters south of Singapore showing radar signatures of a strong tropical squall line ("Sumatra Squall") is compared with coincident and collocated weather radar data. Squall line features such as the gust front, areas of updraft convergence, and rain areas are identified. Possible attenuation effects from the rain drops in the atmosphere under very heavy rain (rain rate >100 mm/h) is suggested. In addition, the possibility of extracting the associated geophysical parameters, i.e., rain rate and wind speed from SAR imagery is investigated. The rain rate is estimated from the attenuation signature in the SAR image. Comparison between the estimated rain rate and weather radar rain rate shows consistency. Wind speed associated with the squall line is estimated based on the CMOD4 wind scatterometer model. The estimated wind speed pattern appears to be in agreement with the observed squall line structure. Possible errors in the wind estimation due to effects of rain are suggested.

An automatic identification of clutter and anomalous propagation in polarization-diversity weather radar data using neural networks

Abstract: Radar polarization measurements have mostly been used to improve rainfall estimation and hydrometeor characterization. The authors extend the use of such measurements to the problem of ground clutter recognition, including the case when this problem is associated with anomalous propagation of the electromagnetic wave. They present a methodology used for recognizing both clutter and meteorological targets. The methodology is based on the knowledge of the scattering properties of the targets, as provided by the polarization measurements and the use of the neural network approach that performs the classification. The results show that if circular polarization is used, the circular depolarization ratio and the degree of polarization are good discriminators of clutter and nonclutter. They have used data from the Alberta polarization diversity radar to build an automatic decision process using a feedforward neural network. After they trained the neural network, they tested the classifier for two common clutter situations: when there is an electromagnetic wave anomalous propagation and when targets from rain are mixed with the clutter close to the radar.

Precipitation Estimates over the Baltic Sea: Present State of the Art

Abstract: Precipitation is one of the main components in the water balance, and probably the component determined with the greatest uncertainties. In the present paper we focus on precipitation (mainly rain) over the Baltic Sea as a part of the BALTEX project to examine the present state of the art concerning different precipitation estimates over that area. Several methods are used, with the focus on 1) interpolation of available synoptic stations; 2) a mesoscale analysis system including synoptic, automatic, and climate stations, as well as weather radar and an atmospheric model; and 3) measurements performed on ships. The investigated time scales are monthly and yearly and also some long-term considerations are discussed. The comparison shows that the differences between most of the estimates, when averaged over an extended period and a larger area, are in the order of 10-20%, which is in the same range as the correction of the synoptic gauge measurements due to wind and evaporation losses. In all data sets using gauge data it is important to include corrections for high winds. To improve the structure of precipitation over sea more focus is to be put on the use of radar data and combinations of radar data and other data. Interpolation methods that do not consider orographic effects must treat areas with large horizontal precipitation gradients with care. Due to the large variability in precipitation in time and space, it is important to use long time periods for climate estimates of precipitation Ship measurements are a valuable contribution to precipitation information over sea, especially for seasonal and annual time scales.

Convective weather detection by general aviation pilots with conventional and data-linked graphical weather information sources

Abstract: This study compares how well general aviation (GA) pilots detect convective weather in flight with different weather information sources. A flight test was conducted in which GA pilot test subjects were given different in-flight weather information cues and flown toward convective weather of moderate or greater intensity. The test subjects were not actually flying the aircraft, but were given pilot tasks representative of the workload and position awareness requirements of the en route portion of a cross country GA flight. On each flight, one test subject received weather cues typical of a flight in visual meteorological conditions (VMC), another received cues typical of flight in instrument meteorological conditions (IMC), and a third received cues typical of flight in IMC but augmented with a graphical weather information system (GWIS). The GWIS provided the subject with near real time data-linked weather products, including a weather radar mosaic superimposed on a moving map with a symbol depicting the aircraft's present position and direction of track. At several points during each flight, the test subjects completed short questionnaires which included items addressing their weather situation awareness and flight decisions. In particular, test subjects were asked to identify the location of the nearest convective cells. After the point of nearest approach to convective weather, the test subjects were asked to draw the location of convective weather on an aeronautical chart, along with the aircraft's present position. This paper reports preliminary results on how accurately test subjects provided with these different weather sources could identify the nearest cell of moderate or greater intensity along their route of flight.

Wind Structure in a Supercell Thunderstorm as Measured by a UHF Wind Profiler

Abstract: A mesocyclone associated with a tornadic supercell passed almost directly over the Lamont, Oklahoma, 404-MHz wind profiler on 24 May 1998. The archived spectral moment data, including 6-min resolution radial velocity measurements from the vertical and two oblique beams of the profiler, provided a rare opportunity to construct a detailed time–height section of the three-dimensional wind structure of a severe convective storm near and in its mesocyclone. Supplemental information used to create this cross section was provided by nearby operational Next Generation Weather Radar/Weather Surveillance Radar (NEXRAD/WSR-88D) radars, as well as visual and surface observations. The most difficult challenge in analyzing the profiler data was the removal of hydrometeor fall-speed contamination in order to determine the true air motions. Since the profiler beams saturate under heavy precipitation conditions, the use of the returned signal power in the profiler beams to estimate precipitation fall speeds was n...

Power demand estimation system and its estimation method

Abstract: PROBLEM TO BE SOLVED: To estimate power demand accurately and carefully. SOLUTION: Power demand is estimated, making use of the two pieces of information referring to the regional distribution of weather forecast information such as temperature, humidity and the regional characteristics of the power demand. More specifically, an estimation model maker 13 makes a local weather forecast model tinged with observation data by a weather radar, a ground rain gauge, etc., based on GPV data delivered from the Japan Meterological Agency or an overseas agency, and makes more detailed and accurate weather forecast data. A statistical analyzer 14 puts the regional characteristics of power demand into a database in advance, based on the past actual results. Then in forecasting processing, this system obtains the power demand corresponding to a forecast temperature and humidity separately for each region, referring to the actual results data base, and finally obtains the quantity of power demand in the whole region. In this case, this can also make the weather conditions and power demand correspond to each other by each region by a return system or the like, coupled with information about a rain quantity, wind direction, wind speed, etc. COPYRIGHT: (C)2003,JPO

A simple based on DSP antenna controller of weather radar

Abstract: This paper describes a simple based on DSP antenna controller which integrates SDC (synchro to digital converter) and RDC (resolver to digital converter) with antenna control logic calibration of the antenna angular code and adjustment of the radar antenna control system. It makes the antenna control system hardware simple, compact, stable, low-cost, highly flexible and easily maintainable. It is affordable for a low-cost X-band weather radar of weather modification operation. The paper starts with a simple description of the hardware architecture and then analyzes the angular resolution and accuracy. Finally it presents auto-angle code calibration and adjustment of the radar antenna control system.

Operational bright-band snow level detection using doppler radar

Abstract: A method to detect the bright-band snow level from radar reflectivity and Doppler vertical velocity data collection with an atmospheric profiling Doppler radar. The measurement may be made available to the public through the Internet.

NOTES AND CORRESPONDENCE Winter Thunderstorms in Israel: A Study with Lightning Location Systems and Weather Radar

Abstract: A study of the morphology and evolution of winter thunderstorms in Israel and over the eastern Mediterranean was conducted during the 1995‐96 winter season. Electrically active cells were analyzed by combining data from weather radar and an operational lightning positioning and tracking system. This enabled the identification of reflectivity features of electrically active cells, and tracing of the spatial and temporal evolution of thunderstorms. The results show that, in winter, rain clouds became thunderclouds if their echo top was higher than 6500 m (at a temperature level colder than 2308C), provided that the reflectivity at the level of the 2108C isotherm was larger than 35 dBZ. The period between the first radar echo and the first detected lightning flash (probably a ground flash) was found to be 10‐15 min, a period at which the top of the 40-dB Z echo was located higher than the 288C level.

Winter Thunderstorms in Israel: A Study with Lightning Location Systems and Weather Radar

Abstract: A study of the morphology and evolution of winter thunderstorms in Israel and over the eastern Mediterranean was conducted during the 1995–96 winter season. Electrically active cells were analyzed by combining data from weather radar and an operational lightning positioning and tracking system. This enabled the identification of reflectivity features of electrically active cells, and tracing of the spatial and temporal evolution of thunderstorms. The results show that, in winter, rain clouds became thunderclouds if their echo top was higher than 6500 m (at a temperature level colder than −30°C), provided that the reflectivity at the level of the −10°C isotherm was larger than 35 dBZ. The period between the first radar echo and the first detected lightning flash (probably a ground flash) was found to be 10–15 min, a period at which the top of the 40-dBZ echo was located higher than the −8°C level.