The Experts below are selected from a list of 2223 Experts worldwide ranked by ideXlab platform
Chandra S. Pathak - One of the best experts on this subject based on the ideXlab platform.
-
influence of temporal resolution of rain gage data on bias correction procedures for NEXRAD estimates
World Environmental And Water Resources Congress 2012, 2012Co-Authors: Aneesh Goly, Chandra S. Pathak, Ramesh S. V. Teegavarapu, Kenneth RomieAbstract:Bias corrections of radar data using ground truth is essential and critical step in generation of viable precipitation data sets. The improvement in the radar data achieved through the correction procedures depend on several factors including available rain gage data, gage density and reliability of ground truth. Availability of rain gage data at the same temporal resolution as that of radar data is essential and may not be possible in many instances. In those situations, correction procedures adopted for up-scaling or down-scaling the bias-correction factors need to be evaluated thoroughly. In the current study, bias correction procedures using spatial interpolation and optimal weighting methods used for adjustment of NEXRAD based rainfall estimates are assessed. Fifteen minute NEXRAD-based precipitation data available from South West Florida Water Management District (SWFWMD) provided by OneRain Inc. are improved using NOAA and SWFWMD rain gage data available at temporal resolutions of 15 minutes, one hour and a day. All the bias correction methods are evaluated using several performance measures. Data from a minimum of forty three and a maximum of 182 rain gages are used for improvement of NEXRAD data from years 1994-2007. Results from this study highlight the difficulties in applying bias corrections procedures with data sets of different temporal resolutions and performances of different spatial interpolation methods.
-
Comparison of NEXRAD and Rain Gauge Precipitation Measurements in South Florida
Journal of Hydrologic Engineering, 2009Co-Authors: Courtney Skinner, Frederick Bloetscher, Chandra S. PathakAbstract:The South Florida Water Management District (SFWMD) relies on a network of nearly 300 rain gauges in order to provide rainfall data for use in operations, modeling, water supply planning, and environmental projects. However, the prevalence of convective and tropical disturbances in South Florida during the wet season presents a challenge in that the current rain gauge network may not fully capture rain events that demonstrate high spatial variability. Next Generation Radar (NEXRAD) technology offers the advantage of providing a spatial account of rainfall, although the quality of radar-rainfall measurements remains largely unknown. The comparison of rainfall estimates from a gauge-adjusted, NEXRAD-based product developed by the OneRain Company with precipitation measurements from SFWMD rain gauges was performed for the Upper and Lower Kissimmee River Basins over a four-year period from 2002 to 2005. Overall, NEXRAD was found to underestimate rainfall with respect to the rain gauges for the study period, d...
-
Geo-Spatial Comparison of Rain Gauge and NEXRAD Data for Central and South Florida
World Environmental and Water Resources Congress 2008, 2008Co-Authors: Chandra S. Pathak, Baxter E. VieuxAbstract:The South Florida Water Management District (District) is responsible for managing water resources in 16-counties over a 46,439-square kilometer (17,930 square-mile) area. The area extends from Orlando to Key West and from the Gulf Coast to the Atlantic Ocean and contains the country’s second largest lake – Lake Okeechobee and the world famous Everglades wetlands. The District operates approximately 3,000 kilometers (~1,800 miles) of canals, 22 major pump stations and 200 water control structures. Nearreal-time rainfall data are used in operation of these pumps and water control structures. The District uses a network of approximately 287 active rain gauge stations that cover the more populated and environmentally sensitive areas under its management and provide data for this purpose. Four NEXRAD (Next Generation Weather Radar) sites operated by the National Weather Service cover the region. Since 2002 the District began to acquire NEXRAD data coverage. Corporate access of 15-minute, rain gauge-adjusted NEXRAD data, for each of the 2 x 2 km cells in the grid covering the District, was a major objective of the acquisition. The District has been receiving the NEXRAD data two types of datasets - near-real time (NRT) and end-of-month (EOM). District is using ArcIMS based application for NEXRAD data retrieval. The application provides varied spatially and temporally integrated datasets in tabular and image formats. This paper compares results of geo-spatial analysis of clusters of rain gauge and NEXRAD data. The data used in the analysis includes rain gauge data and the NEXRAD rainfall data that was collected during 1995-2005 at 2 x 2 km resolution. A set of clusters of rain gauges and a regular array of analysis blocks that were 20 x 20 km in size for the NEXRAD data were used to account for variability of the rainfall processes and local rainfall patterns. The spatial autocorrelations of the rain gauge and NEXRAD rainfall were identified using a semivariogram approach at daily timescale. The model fitting to the semivariograms were performed on data from 1998-2005. The range parameter of the semivariograms from rain gauge and NEXRAD rainfall data sets were compared.
-
Improvement of NEXRAD Rainfall Data for Central and South Florida
World Environmental and Water Resources Congress 2008, 2008Co-Authors: Chandra S. Pathak, Baxter E. VieuxAbstract:The South Florida Water Management District (District) is responsible for managing water resources in 16-counties over a 46,439-square kilometer (17,930 square-mile) area. The area extends from Orlando to Key West and from the Gulf Coast to the Atlantic Ocean and contains the country's second largest lake — Lake Okeechobee and the world famous Everglades wetlands. The District operates approximately 3,000 kilometers (∼1,800 miles) of canals and over 500 water control structures. Near-real-time NEXRAD rainfall data and rain gage network is used to manage water resources in South Florida. The District uses a network of approximately 287 active rain gage stations that cover the more populated and environmentally sensitive areas. Five NEXRAD (Next Generation Weather Radar) sites operated by the National Weather Service cover the region. In conjunction with three of the other five water management districts in Florida, the District has acquired processed radar data from OneRain (formerly NEXRAIN Corporation) since July 2002. The 15-minute radar rainfall data was derived from the 2-km x 2-km high-resolution precipitation product, which was produced from NWS Level 3 — NEXRAD reflectivity. To achieve improved accuracy, gage-adjusted radar rainfall data were derived. This paper provides details on improvements that were made to existing radar rainfall data processed and provided for the District. A bias correction methodology was identified to improve data quality and accuracy in the existing radar rainfall data. The method was applied to existing rainfall data and its performance evaluated and assessed. The improvement obtained through reprocessing the existing radar rainfall data was summarized through data comparison of annual totals and by comparison to gage accumulations over the three watershed areas. In addition, Level 2 NEXRAD reflectivity data (also 2-km x 2-km)from surrounding radars were processed to estimate radar rainfall data using a standard Z-R relationship. During a validation event, the radar rainfall data derived from Level 2 produced better agreement and more accurate rainfall than either the existing radar rainfall product or the reprocessed data. The NEXRAD data quality improvement process performed in this study increased the amount of rainfall through application of the spatially variable bias correction, produced more consistent results through verification at control gages using statistical performance measures.
-
Impact of Using Radar Rainfall Data in Water Budgets for South Florida Stormwater Treatment Areas
World Environmental and Water Resources Congress 2007, 2007Co-Authors: R. Scott Huebner, Wossenu Abtew, Chandra S. PathakAbstract:The South Florida Water Management District (District) currently operates 6 Stormwater Treatment Areas (STAs) located in the Everglades Agricultural Area (EAA) covering a total of 16,200 hectares. STAs are large wetland filter marshes that receive agricultural runoff in an effort to reduce suspended solids and nutrients prior to discharge to environmentally sensitive waters in the Everglades. One of the tools used to assess and manage these areas is an annual water budget analysis and report. The District is acquiring rain gage-adjusted, 15-minute NEXRAD radar rainfall data from a vendor, in conjunction with the other Florida water management districts (Huebner, et al, 2003). The NEXRAD data provide 2 km by 2 km areal estimates of rainfall. In South Florida, rainfall usually comprises up to approximately 10 percent of an STA's annual inflow. It is not unusual for annual water budget errors to be on the same order (Abtew, 2005; Liyanage and Huebner, 2005). Due to the nature of storm cells during the wet season (June through October) in South Florida, using rain-gage values of rainfall for treatment areas that span up to 6,700 hectares has the potential to introduce a significant error in the water budget. Using radar rainfall data for this purpose introduces its own set of errors associated with this rainfall estimation technology. Using NEXRAD and rain-gage rainfall data and other water budget data for three STAs over a two-year period, this analysis concludes that, for the years and STAs examined, NEXRAD data provided results that were consistent with data from the rain gages in annual water budget calculations and represented spatial variation of rainfall across an STA's footprint.
John Lanicci - One of the best experts on this subject based on the ideXlab platform.
-
In-Cockpit NEXRAD Products: Training General Aviation Pilots
2016Co-Authors: Michael Vincent, Elizabeth L. Blickensderfer, Robert Thomas, Maryjo Smith, John LanicciAbstract:Recent developments in avionics have allowed pilots of General Aviation (GA) aircraft to access more in-flight information than ever before, among them being data link weather services. However data link resources, namely next generation radar (NEXRAD), possess discrete limitations which can lead pilots into dangerous situations if they do not interpret the information correctly. The present study evaluated a training module designed to help pilots interpret and use data link NEXRAD weather information. GA pilots in the Midwest and Northeastern U.S. completed a face-to-face lecture course which covered the capabilities and limitations of NEXRAD based weather products and included paper based scenarios to give course participants practice using NEXRAD as a tool for decision making. A comparison of Pre- vs. post- test performance indicated that pilots had significant increases in radar knowledge, performance on application scenarios, and self-efficacy after completing the training. BACKGROUND Understanding current weather conditions is essential for the safety of flight, especially for pilots of General Aviation (GA) aircraft, as the performance capabilities of those aircraft limit the pilot’s ability to avoid meteorological hazards. Fortunately, pilots have several resources to understand weather conditions and to help them avoid dangerous situations. For example, preflight planning tool
-
In-Cockpit NEXRAD Products Training General Aviation Pilots
Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 2013Co-Authors: Michael Vincent, Elizabeth L. Blickensderfer, Robert Thomas, Maryjo Smith, John LanicciAbstract:Recent developments in avionics have allowed pilots of General Aviation (GA) aircraft to access more in-flight information than ever before, among them being data link weather services. However data link resources, namely next generation radar (NEXRAD), possess discrete limitations which can lead pilots into dangerous situations if they do not interpret the information correctly. The present study evaluated a training module designed to help pilots interpret and use data link NEXRAD weather information. GA pilots in the Midwest and Northeastern U.S. completed a face-to-face lecture course which covered the capabilities and limitations of NEXRAD based weather products and included paper based scenarios to give course participants practice using NEXRAD as a tool for decision making. A comparison of Pre- vs. post- test performance indicated that pilots had significant increases in radar knowledge, performance on application scenarios, and self-efficacy after completing the training.
M. Petitdidier - One of the best experts on this subject based on the ideXlab platform.
-
© European Geosciences Union 2004
2015Co-Authors: P. Kaf, M. PetitdidierAbstract:Arecibo using NEXRAD radar and disdrometer dat
-
An attempt to calibrate the UHF strato-tropospheric radar at Arecibo using NEXRAD radar and disdrometer data
Annales Geophysicae, 2004Co-Authors: P. Kafando, M. PetitdidierAbstract:Abstract. The goal of this paper is to present a methodology to calibrate the reflectivity of the UHF Strato-Tropospheric (ST) radar located at NAIC in Puerto Rico. The UHF lower relevant altitude is at 5.9km, the melting layer being at around 4.8km. The data used for the calibration came from the observations of clouds, carried out with Strato-Tropospheric dual-wavelength (UHF and VHF) radars and a disdrometer; those instruments being located on the NAIC site in Arecibo, Puerto Rico. The National Weather Service operates other instruments like the radiosondes and the NEXRAD Radar in other sites. The proposed method proceeds in two steps. The first consists of the comparison between the NEXRAD reflectivity and the reflectivity computed from the drop size distributions measured by the disdrometer for one day with a noticeable rainfall rate. In spite of the distance of both instruments, the agreement between the reflectivities of both instruments is enough good to be used as a reference for the UHF ST radar. The errors relative at each data set is found to be 2.75dB for the disdrometer and 4dB for the NEXRAD radar, following the approach of Hocking et al. (2001). The inadequacy between the two sampled volume is an important contribution in the errors. The second step consists of the comparison between the NEXRAD radar reflectivity and the UHF non-calibrated reflectivity at the 4 altitudes of common observations during one event on 15 October 1998. Similar features are observed and a coefficient is deduced. An offset around 4.7dB is observed and the correlation factor lies between 0.628 and 0.730. According to the errors of the data sets, the precision on the calibration is of the order of 2dB. This method works only when there are precipitation hydrometeors above the NAIC site. However, the result of the calibration could be applied to other data obtained during the campaign, the only constraint being the same value of the transmitter power. Key words. Meteorology and atmospheric dynamics (tropical meteorology; remote sensing; instruments and techniques)
Thomas H Kunz - One of the best experts on this subject based on the ideXlab platform.
-
quantifying animal phenology in the aerosphere at a continental scale using NEXRAD weather radars
Ecosphere, 2012Co-Authors: Jeffrey F Kelly, Ryan J Shipley, Phillip B Chilson, Kenneth Howard, Winifred F Frick, Thomas H KunzAbstract:One of the primary ecological manifestations of climate change is a shift in the timing of events in a species' annual cycle. Such phenological shifts have been documented in numerous taxa, but data for animals have been derived primarily from human observers rather than networks of instruments used for remote sensing. The potential to use the network of weather radars in the United States (NEXRAD) to remotely sense animal phenologies could advance our understanding of the spatiotemporal scaling of phenologies in relation to shifts in local and regional climate. We tested the utility of NEXRAD radar products for quantifying the phenology of the purple martin (Progne subis) at summer roost sites in the United States. We found that the maximum radar reflectivity value in the hour before local sunrise above purple martin roost sites contained a strong phenological signal of significantly increased radar reflectivity during June, July, and August 2010. The seasonal pattern in this radar signal matched our expectation of the timing of formation and dissipation of these seasonal roosts. Radar reflectivity was greater and less variable when considering roosts close to NEXRAD stations (<25 km) than when including all 358 documented roosts; there was a negative relationship between maximum reflectivity and the distance between a roost and the nearest NEXRAD. Our results suggest that: (1) mosaicked NEXRAD radar products are a valuable source of information on the phenology of bioscatter in the aerosphere; (2) citizen scientists who document the locations of roosts on the ground are providing critical information for advancing our understanding of animal phenology and aeroecology; and (3) ongoing research that examines spatiotemporal relationships among radar-derived phenologies in airborne organisms, climate, and land cover change are likely to provide further insights.
-
Quantifying animal phenology in the aerosphere at a continental scale using NEXRAD weather radars
Ecosphere, 2012Co-Authors: Jeffrey F Kelly, Phillip B Chilson, Kenneth Howard, Winifred F Frick, J. Ryan Shipley, Thomas H KunzAbstract:One of the primary ecological manifestations of climate change is a shift in the timing of events in a species' annual cycle. Such phenological shifts have been documented in numerous taxa, but data for animals have been derived primarily from human observers rather than networks of instruments used for remote sensing. The potential to use the network of weather radars in the United States (NEXRAD) to remotely sense animal phenologies could advance our understanding of the spatiotemporal scaling of phenologies in relation to shifts in local and regional climate. We tested the utility of NEXRAD radar products for quantifying the phenology of the purple martin (Progne subis) at summer roost sites in the United States. We found that the maximum radar reflectivity value in the hour before local sunrise above purple martin roost sites contained a strong phenological signal of significantly increased radar reflectivity during June, July, and August 2010. The seasonal pattern in this radar signal matched our expectation of the timing of formation and dissipation of these seasonal roosts. Radar reflectivity was greater and less variable when considering roosts close to NEXRAD stations (
-
Analyzing NEXRAD doppler radar images to assess nightly dispersal patterns and population trends in Brazilian free-tailed bats (Tadarida brasiliensis).
Integrative and Comparative Biology, 2007Co-Authors: Jason W. Horn, Thomas H KunzAbstract:Operators of early weather-surveillance radars often observed echoes on their displays that did not behave like weather pattern, including expanding ring-like shapes they called angels. These echoes were caused by high-flying insects, migrating birds, and large colonies of bats emerging from roosts to feed. Modern weather-surveillance radar stations in the United States (NEXt-generation RADar or NEXRAD) provide detailed images that clearly show evening bat emergences from large colonies. These images can be used to investigate the flight behavior of groups of bats and population trends in large colonies of Brazilian free-tailed bats (Tadarida brasiliensis) in south-central Texas which are clearly imaged by local NEXRAD radar stations. In this study, we used radar reflectivity data from the New Braunfels, Texas NEXRAD station to examine relative colony size, direction of movement, speed of dispersion, and altitude gradients of bats from these colonies following evening emergence. Base reflectivity clear-air-mode Level-II images were geo-referenced and compiled in a GIS along with locations of colonies and features on the landscape. Temporal sequences of images were filtered for the activity of bats, and from this, the relative size of bat colonies, and the speed and heading of bat emergences were calculated. Our results indicate cyclical changes in colony size from year to year and that initial headings taken by bats during emergence flights are highly directional. We found that NEXRAD data can be an effective tool for monitoring the nightly behavior and seasonal changes in these large colonies. Understanding the distribution of a large regional bat population on a landscape scale has important implications for agricultural pest management and conservation efforts.
P. Kafando - One of the best experts on this subject based on the ideXlab platform.
-
An attempt to calibrate the UHF strato-tropospheric radar at Arecibo using NEXRAD radar and disdrometer data
Annales Geophysicae, 2004Co-Authors: P. Kafando, M. PetitdidierAbstract:Abstract. The goal of this paper is to present a methodology to calibrate the reflectivity of the UHF Strato-Tropospheric (ST) radar located at NAIC in Puerto Rico. The UHF lower relevant altitude is at 5.9km, the melting layer being at around 4.8km. The data used for the calibration came from the observations of clouds, carried out with Strato-Tropospheric dual-wavelength (UHF and VHF) radars and a disdrometer; those instruments being located on the NAIC site in Arecibo, Puerto Rico. The National Weather Service operates other instruments like the radiosondes and the NEXRAD Radar in other sites. The proposed method proceeds in two steps. The first consists of the comparison between the NEXRAD reflectivity and the reflectivity computed from the drop size distributions measured by the disdrometer for one day with a noticeable rainfall rate. In spite of the distance of both instruments, the agreement between the reflectivities of both instruments is enough good to be used as a reference for the UHF ST radar. The errors relative at each data set is found to be 2.75dB for the disdrometer and 4dB for the NEXRAD radar, following the approach of Hocking et al. (2001). The inadequacy between the two sampled volume is an important contribution in the errors. The second step consists of the comparison between the NEXRAD radar reflectivity and the UHF non-calibrated reflectivity at the 4 altitudes of common observations during one event on 15 October 1998. Similar features are observed and a coefficient is deduced. An offset around 4.7dB is observed and the correlation factor lies between 0.628 and 0.730. According to the errors of the data sets, the precision on the calibration is of the order of 2dB. This method works only when there are precipitation hydrometeors above the NAIC site. However, the result of the calibration could be applied to other data obtained during the campaign, the only constraint being the same value of the transmitter power. Key words. Meteorology and atmospheric dynamics (tropical meteorology; remote sensing; instruments and techniques)
-
An attempt to calibrate the UHF strato-tropospheric radar at Arecibo using NEXRAD radar and disdrometer data
Annales Geophysicae, 2004Co-Authors: P. Kafando, Monique PetitdidierAbstract:The goal of this paper is to present a methodology to calibrate the reflectivity of the UHF Strato-Tropospheric (ST) radar located at NAIC in Puerto Rico. The UHF lower relevant altitude is at 5.9km, the melting layer being at around 4.8km. The data used for the calibration came from the observations of clouds, carried out with Strato-Tropospheric dual-wavelength (UHF and VHF) radars and a disdrometer; those instruments being located on the NAIC site in Arecibo, Puerto Rico. The National Weather Service operates other instruments like the radiosondes and the NEXRAD Radar in other sites. The proposed method proceeds in two steps. The first consists of the comparison between the NEXRAD reflectivity and the reflectivity computed from the drop size distributions measured by the disdrometer for one day with a noticeable rainfall rate. In spite of the distance of both instruments, the agreement between the reflectivities of both instruments is enough good to be used as a reference for the UHF ST radar. The errors relative at each data set is found to be 2.75dB for the disdrometer and 4dB for the NEXRAD radar, following the approach of Hocking et al. (2001). The inadequacy between the two sampled volume is an important contribution in the errors. The second step consists of the comparison between the NEXRAD radar reflectivity and the UHF non-calibrated reflectivity at the 4 altitudes of common observations during one event on 15 October 1998. Similar features are observed and a coefficient is deduced. An offset around 4.7dB is observed and the correlation factor lies between 0.628 and 0.730. According to the errors of the data sets, the precision on the calibration is of the order of 2dB. This method works only when there are precipitation hydrometeors above the NAIC site. However, the result of the calibration could be applied to other data obtained during the campaign, the only constraint being the same value of the transmitter power.
