ERAD 2012 - THE SEVENTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY

Dallas Fort Worth Urban Demonstration Network

V. Chandrasekar1 and Brenda Philips1,2 and the DFW team

1Colorado State University, USA, Chandra@engr.colostate.edu 2University of Massachusetts, USA

(Dated: 30 May 2012)

Presenting author V. Chandrasekar

1. Introduction The U.S. National Science Foundation (NSF)’s Engineering Research Center (ERC) for Collaborative Adaptive Sensing

of the Atmosphere (CASA) is dedicated to revolutionizing our ability to observe, understand, predict, and respond to hazardous weather events using a dense network of small, low-power radars that can sense the lower atmosphere [1]. The advantages of the CASA radars include enhanced sampling of precipitation and winds near the ground. These smaller and less-expensive radars are deployed at a distance of about 30 km from each other, which is much closer than that in the current operational radar network, i.e., the WSR-88D Next Generation Doppler Radar (NEXRAD). CASA has adopted a new observation methodology termed distributed collaborative adaptive sensing (DCAS) to collaboratively operate the radar networks and adapt them to changing atmospheric conditions, prevailing weather information and the needs of various end users. The overall goal of the DCAS observing methodology is to save lives and reduce property losses through improving precipitation estimates for flood prediction, reducing the tornado false alarm rate, improving severe storm forecasts, etc. CASA, in collaboration with the NCTCOG, is embarking on a project to create the Dallas–Fort Worth Urban Demonstration Network centered on the deployment of a network of eight boundary-layer observing, dual-pol, X-band radars to demonstrate the delivery of improved forecasts, warnings, and responses in a densely populated urban environment.

The system to be deployed in the DFW urban test bed is based on the new technologies and end user research conducted by the CASA project. CASA is an NSF Engineering Research Center dedicated to revolutionizing our ability to observe, understand, predict, and respond to hazardous weather events. The center has pursued an innovative, densely networked radar sensing paradigm to overcome the resolution and coverage limitations of traditional weather radars using low-cost, densely networked radar systems (McLaughlin et al., 2010). The short range and close spacing of these radars give them the ability to scan low to the ground with very high spatial resolution. Overlapping coverage allows each voxel in the network to be simultaneously viewed by two or more radars, allowing for multi-Doppler wind vector retrievals and a solution to the increased attenuation experienced at X-band. The CASA concept and related enabling technologies developed by the CASA enterprise have been evaluated and validated in a prototype system-level test bed located in southwestern Oklahoma. CASA brings the following to the DFW Urban Demonstration Network: expertise in radar engineering and meteorology, in networked systems (Junyent and Chandrasekar, 2009; Zink et al., 2010), precipitation estimation (Wang and Chandrasekar, 2010), real-time analysis and numerical weather prediction (Brewster et al., 2010), integrated warning systems and decision-making (Philips et al., 2010), and societal vulnerability.

2. DFW Urban Demonstration Network Overview High-level goals of the DFW Urban Demonstration Network

1. To develop high-resolution two- and three-dimensional mapping of current atmospheric conditions, focusing on the boundary layer, to detect and forecast severe wind, tornado, hail, ice, and flash flood hazards.

2. To create impacts-based, neighborhood-scale warnings and forecasts for a range of public and private decision-makers that result in measurable benefit for public safety and the economy.

3. To demonstrate the value of collaborative, adaptive X-band radar networks to existing and future sensors, products, performance metrics, and decision-making; and assess optimal combinations of observing systems.

4. To develop models for federal/municipal/private partnerships to introduce new observation technologies for on-going operational and interdisciplinary weather system research.

a) Radars. We plan to operate an 8-node, multi-Doppler, dual-polarization radar network covering portions of 12 out of

the 16 counties in the DFW metroplex and the majority of the 6.5 million people in the area. Lowest beam coverage is planned at an average 270 m AGL (ranging from 100 – 500 m) with 100 m gate spacing.

ERAD 2012 - THE SEVENTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY

Figure 1. Example of 8-radar layout, in DFW. b) Other Observations. CASA will take advantage of existing sensors, such as WSR-88D, TDWR, and rain gauges for

creating new products and for validation purposes. In addition, as a result of the network, we are planning on private, federal, state and academic organizations to integrate additional sensors into the test bed. Further, CASA participants are actively pursuing several avenues for procuring additional weather information from across the Dallas–Fort Worth metroplex. Specifically, CASA is negotiating with CASA industry partners to collaboratively deploy and test sensors, including profilers and radiometers. A multiplicity of sensors will allow testing of network-of-network concepts.

c) IT infrastructure. IT infrastructure for data mining, radar control, and data dissemination will be housed at NWS

Southern Region Headquarters (SRH). SRH is providing connectivity into the Dallas–Fort Worth Weather Forecast Office to ensure data flow, assist with integrating CASA data into AWIPS2, and create web-based interfaces that will allow research in on-demand forecasts/nowcasts and experimental product display.

d) Products. CASA will offer a suite of high-resolution products to the DFW WFO. e) Stakeholders. Our primary local partner is the North Central Texas Council of Governments (NCTCOG) through their Office of

Emergency Preparedness, which has strong ties to the emergency management (EM) community. The NCTCOG coordinates activities in transportation, water management, and aviation that can benefit its membership in a 16-county region around the DFW metroplex. They have a history of successfully coordinating and supporting innovative projects. CASA has signed a memorandum of understanding (MOU) with the NCTCOG to redeploy, install, and operate the radar network and engage a variety of stakeholders from surface transportation, aviation, utilities, corporate headquarters, and event arenas. NCTCOG has formed a CASA steering committee composed of local emergency managers (EM) and elected officials to guide the operation and ongoing sustainability of the Urban Demonstration Network. CASA is also establishing strong connections to the large, vibrant regional EM community of over 600 EMs. The directors of emergency management in Fort Worth and Dallas are co-chairs of the CASA/NCTCOG steering committee. Creating impacts-based products for the EM community will be a core focus of the Urban Demonstration Network. We have already distributed a survey on technology usage and tornado warning practice and have conducted a focus group on flash flood warnings. In addition, CASA and NCTCOG are developing a community-based model for radar operations where emergency managers and their jurisdictions host a CASA radar.

ERAD 2012 - THE SEVENTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY

f) NOAA Stakeholders: CASA has been working very closely with the Meteorologist-in-Charge (MIC) of the DFW WFO to define the weather

information needs of the DFW metroplex and its goals for the program. Thus, the DFW WFO will play a central role in demonstrating how these high-resolution, urban-scale products may enhance interpretive services provided by forecasters for public safety and for other government organizations. Since a primary focus will be on forecaster/emergency manager interactions, we see the Urban Demonstration Network and the products it generates as improving an already strong relationship between the DFW Emergency Managers and the DFW WFO, and providing approaches and products that could be used in other forecast offices. We are also working with the Hydrologist-in-Charge at the River Forecast Center to define their precipitation estimation and urban flood forecasting needs across the metroplex.

3. Demonstration Network Themes

The various research and operational demonstrations can be broadly classified into three areas:

1) Severe storm forecasting and nowcasting, 2) urban floods, and 3) end user decision-making impacts. A detailed description of each of these research areas is beyond the scope of this paper, and since this paper is scheduled in a QPE (Quantitative Precipitation Estimation ) session, the QPE and urban flash flood aspect alone is discussed in detail.

3.1 Urban Flash Flood and Hydrology For urban environments, it is widely acknowledged that fine-scale, accurate precipitation measurements are a critical factor for effective flash flood warnings, especially in regions such as North Texas. Extensive urban development decreases the response time of urban watersheds to rainfall and increases the chance of localized flooding events over a small spatial domain. The DFW area, with its rapid development, is especially sensitive to this issue. This project will demonstrate and evaluate how the suite of CASA QPE products can enhance urban flash flood warning and hydrologic decision-making processes for the River Forecast Center (RFC) and the Fort Worth Weather Forecast Office (WFO). The dual-pol X-band CASA radars in the DFW Urban Demonstration Network will provide quantitative precipitation estimates based on dual-polarized differential propagation phase (Kdp) values at very high spatial (100 m) and temporal resolution (1 minute) and at low elevations (100 m – 500 m AGL) across the metroplex. A rapidly updating (every minute) nowcast product will project rainfall rates out to 30 minutes. In addition, CASA will produce a real-time analysis every 30 minutes based on assimilating all available weather information. This analysis provides the initial conditions for a deterministic 3-hour QPF. CASA QPE Methodology

The CASA QPE methodology is predominantly a Kdp (specific differential phase)-based technique (Bringi and Chandrasekar, 2001). Wang and Chandrasekar (2009) proposed an adaptive algorithm to estimate Kdp that has better range resolution in intense rain cells to capture small-scale variability [6]. This estimation method is implemented in the CASA QPE system to substantially reduce the fluctuation in light rain and the bias at heavy rain. Fundamentally, radar QPE is built based on the relations between rain microphysics and radar observables (Bringi and Chandrasekar, 2001). The R-Kdp relation can be expressed in a power law form as:

bdpaKR = (1)

where a, b are coefficients given by different meteorological properties. A wide range of coefficients has been given for the R-Kdp power law relation at both S-band and X-band [7]. Ryzhkov et al. (2005) suggested a KOUN’s R-Kdp relation at S-band for the prototype WSR-88D system [8], which was scaled to X-band as below with respect to wavelength for rainfall conversion in the CASA test bed. In addition, a composite Kdp-based rainfall was computed with observations from multiple radars.

791.015.18 dpKR = (2)

Prior to deploying the demonstration testbed in DFW, this system operated in Oklahoma for over five years in the system called the IP-1 testbed. During this period, extensive product development and validation was conducted. The surface rainfall measurements from rain gauges were used to assess and validate the CASA rainfall products. In the center of the CASA IP1 test bed is the Little Washita River watershed; within that about 20 rain gauge stations are deployed (see Fig. 2). The rain gauges are managed by the Agricultural Research Service (ARS) of the U.S. Department of Agriculture (USDA) as part of the Little Washita Micronet. The data collected by the 20 gauges are archived as accumulation in 5-min intervals over every 24-h period. The gauge observations are the baseline for cross-validating comparison with CASA QPE.

ERAD 2012 - THE SEVENTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY

   

The metrics of evaluation include the mean bias, the normalized mean bias, and the normalized standard error (NSE), respectively, defined as follows:

>−>=<< GR RRe (3)

><

>−<=><

G

GRN R

RRe

(4)

><

>−<=

G

GR

RRR

NSE (5)

where brackets denote the sample average and RR and RG represent instantaneous rainfall rate or hourly rainfall accumulation estimated from radar and gauge, respectively. To demonstrate the performance of CASA QPE system, about 42 storm events in the IP1 test bed from the CASA experiments were analyzed, including different storm types such as severe thunderstorm, convective line, widespread stratiform rain, and cold front system. Overall, compared with the gauge measurements, the radar-based rainfall estimations have a very small bias of about 3.74% and a normalized standard error of about 25%. These aggregate numbers show the excellent performance of the CASA QPE system. Fig 3 is a sample product showing the detailed hourly rainfall (running average) point-wise traces against gauges at a gauge location in the Little Washita gauge network for the May 20, 2011, rainfall event (i.e., at gauge number 282 location: Latitude: 34.845039, Longitude: -98.073473). Similarly, Fig 4 shows a snapshot of the hourly rainfall map .

Fig. 3: Hourly rainfall comparison at the location of gauge 282, May 20, 2011

Fig. 4: A sample hourly rainfall map collected on June 14, 2010 storm. Thus the high resolution (space and time) QPE products are ready to serve as inputs to hydrologic and hydraulic models in the DFW region.

The RFC is migrating to a new operational forecast system that has the capability of infusing more advanced hydrologic models and new technologies into the forecast process. This new system, the community hydrologic prediction system (CHPS), builds on better coordination among all water agencies and improves the accuracy and utility of the entire community’s water-based forecasts. CHPS will also allow for the rapid transfer of collaborative research into NWS operations. The availability of CHPS and CASA radar data combine to provide a unique opportunity to explore new methods for providing localized flood-forecasting in the warning area using distributed hydrologic models.

Fig. 2: Locations of the USDA ground gauges in CASA’s IP1 network

ERAD 2012 - THE SEVENTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY

5. Summary The Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) and the North Central Texas Council of Governments (NCTCOG) are embarking on a five-year project to create the Dallas–Fort Worth (DFW) Urban Demonstration Network. The centerpiece of the Dallas–Fort Worth Urban Demonstration Network will be an 8-node, boundary-layer, dual-polarized, multi-Doppler X-band CASA radar network. Additional in-situ and remote sensors will enable fusion of observations from all sensors. Data products will include single and multi-radar data, vector wind, quantitative precipitation estimation, nowcasting, and analysis and numerical weather prediction products. Research in the DFW Urban Demonstration Network will occur in a quasi-operational environment. New technology and products will be integrated into operational platforms for evaluation by a variety of users during real-time weather events. Users include NWS forecasters and emergency managers and users from transportation, utilities, regional airports, arenas; the media will be added in the near future. In this way, CASA’s multidisciplinary team of engineers, computer scientists, social scientists (sociologists, geographer, economist), meteorologists, and hydrologists will conduct “end-to-end” research from sensor observation to product development and validation linked to end user decision-making, response and value.

Acknowledgment This work was supported by the Engineering Research Centers Program of the National Science Foundation under NSF

Cooperative Agreement No. EEC-0313747 and NOAA.

References 1. Brewster, K., K. Thomas, J. Gao, J. Brotzge, M. Xue, and Y. Wang (2010). A nowcasting system using full physics numerical

weather prediction initialized with CASA and NEXRAD radar data. Preprints, 25th Conf. Severe Local Storms, Denver, CO, Amer. Meteor. Soc

2. Bringi, V. N., and V. Chandrasekar, 2001: Polarimetric Doppler Weather Radar: Principles and Applications. Cambridge University Press, 648 pp.

3. Chandrasekar, V., and Coauthors, 2010: The CASA IP1 test-bed after 5 years operation: Accomplishments, breakthroughs, challenges and lessons learned. Sixth European Conf. on Radar Meteorology, Sibiu, Romania, September 6 - 10, 2010.

4. Junyent, Francesc, V. Chandrasekar, 2009: Theory and Characterization of Weather Radar Networks. J. Atmos. Oceanic Technol., 26, 474–491.

5. McLaughlin, D., and Coauthors, 2009: Short-wavelength technology and the potential for distributed networks of small radar systems. Bull. Amer. Meteor. Soc., 90, 1797–1817.

6. Philips, B., V. Chandrasekar, J. Brotzge, M. Zink, H. Rodriguez, C. League, and W. Diaz (2010). Performance of the CASA radar network during the May 13, 2009 Anadarko tornado. Preprints, 15th Symp. Meteor. Observ. Instrumentation, Atlanta, GA, 17-21 January 17-21, 2010.

7. Ryzhkov, Alexander V., Scott E. Giangrande, Terry J. Schuur, 2005: Rainfall Estimation with a Polarimetric Prototype of WSR-88D. J. Appl. Meteor., 44, 502–515.

8. Wang, Yanting, V. Chandrasekar, 2009: Algorithm for Estimation of the Specific Differential Phase. J. Atmos. Oceanic Technol., 26, 2565–2578.

9. Wang, Yanting, V. Chandrasekar, 2010: Quantitative Precipitation Estimation in the CASA X-band Dual-Polarization Radar Network. J. Atmos. Oceanic Technol., 27, 1665–1676.

10. Zink, M., E. Lyons, D. Westbrook, J. Kurose, and D.L. Pepyne (2010). Closedloop architecture for distributed collaborative adaptive sensing of the atmosphere: meteorological command and control. International Journal of Sensor Networks. 7(1/2): 4-