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Evaluation of the Multifunction Phased Array Radar Planning Process 3 Needs for the Next Generation System Chapter 2 of the Joint Action Group/ Phased Array Radar Project (JAG/PARP) report covers federal agency surveillance needs that can be met with radar. The chapter is based on a survey of the federal agencies using a capabilities questionnaire reproduced in Appendix G of the report. Seven federal agencies responded, including the Department of Defense (DOD) (Air Force, Army and Navy), National Oceanographic and Atmospheric Administration/National Weather Service (NOAA/NWS), the Federal Aviation Administration (FAA) and the Department of Homeland Security (DHS), as well as the Federal Highway Administration (FHWA), the Environmental Protection Agency and the Department of Energy (DOE). The questionnaire responses (not reproduced in the JAG/PARP report) were provided to this committee for review. Tables 3.1 and 3.2 summarize current and future weather and aircraft surveillance needs, as well as other surveillance needs, without identifying the specific agency or agencies stating the need. The JAG/PARP report highlights three main areas (weather surveillance, aircraft surveillance, and other functions) where radar could potentially address the needs of the federal agencies. To a large degree, the stated needs are based on existing missions and capabilities and the report only briefly notes current limitations and potential new missions. However, current system limitations and new or evolving missions are likely to be important in driving future system requirements. MULTI-AGENCY MISSION: OWNERS, USERS, AND BENEFICIARIES The JAG/PARP report speaks to the needs of several agencies and the potential benefits for other agencies; however, it does not clearly speak to the degree of ownership each agency has or would have for a future radar system. This is particularly important in assigning responsibility and defining the requirements for a future radar network. The current owners of US government weather radars are the NOAA/NWS, FAA and DOD. In addition, there are many commercial and research weather radar installations that support a local entity such as a university or a news station. The remaining federal agencies, whether directly using radar information or only relying on derived products from NOAA/NWS or commercial providers, can only be counted as users or downstream beneficiaries. The general public also falls within this category; hence, there are few true owners but numerous beneficiaries.
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Evaluation of the Multifunction Phased Array Radar Planning Process TABLE 3.1. Needs Summary Table – Weather Surveillance. Source: OFCM, 2006. Parameter Current Capability Future Need Derived weather phenomena Instantaneous rain rate, snow, hail, icing, turbulence, winds, microbursts, wind shear, tornado vortex signature All of current plus clouds (base and tops), aerosols (concentration and size distribution), and lightning. Vertical Coverage From 1 km to 70,000 ft.a From surface to 70,000 ft. Horizontal Coverage US states and territories, and surrounding water/bordersb Same as current Range Resolution 250 m (for Doppler moments); 1 km for reflectivity moments Less than 100 m Sensitivity From −20 to 5 dBZ At least as sensitive as current Scanning Mode Clear air and severe weather volume coverage patterns; constantly increasing elevations for one complete volume scan Optimize scanning to better cover the lowest 3 km, using negative angles if necessary Reliability 96% (WSR-88D) At least as reliable as current capability Data Latency Less than 4 minutes (data latency is determined by fact that entire WSR-88D volume scan must be completed before data becomes available) Less than 10 seconds Update Rate 4–6 minutes for a full volume scan (reflectivity versus clear air) 1 minute or less Dual Polarization Planned for deployment on WSR-88D Should be included in any new system Radars Networked? Yesc Yes a More than 70 percent of the lowest 1km of atmosphere is unsampled by WSR-88D. b DOD requires tactical radars for global deployment. c WSR-88D reflectivity products are mosaicked; future need is for radar data from multiple sources that can be automatically fused into single operational pictures in near-real time
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Evaluation of the Multifunction Phased Array Radar Planning Process TABLE 3.2. Needs Summary Table – Aircraft Surveillance. Source: OFCM, 2006. Parameter Current Capability Future Need Derived aircraft parameters Aircraft position Aircraft position, speed, direction, elevation, and type Vertical Coverage From 1 km to 60,000 ft.a From surface to 100,000 ft. Horizontal Coverage All U.S. states and territories, including surronding waters and borders.b Same. Perimeter extends 600 nmi beyond border/coast Range Resolution 1/8 nmi (1/16 nmi at airports) Less than 1/8 nmi. Sensitivity 2.2 m2 cross-section (probability of detection >80%) 0.1 m2 cross-section; targets separated by <0.125 nmi reported as separate targets Scanning Strategy Repeated base scans every minute; fixed surveillance mode does not allow interrogation of individual objects Optimize scanning to better cover the lowest 3 km, using negative angles if necessary; agile scanning to interrogate individual objects Data Latency 120 seconds <2 seconds Update Rate 10–12 seconds en route; 4–5 seconds near terminal <5 seconds Reliability 99% At least as reliable as present units Dual Polarization Not available Should be included in any new system Radars Networked? Yesc Yes. Data available in common, interoperable formats. a Lowest 1 km of atmosphere is unsampled by aircraft surveillance radars over 70% of CONUS. b DOD requires air traffic control radars for global deployment. c The minimal need is for aircraft surveillance radar data readily shared among FAA, DOD, and DHS. The radar aircraft surveillance picture is even murkier. The current systems of US civilian aircraft surveillance radars were acquired, and are operated and maintained, by FAA. These radars are used to detect and track aircraft within FAA airspace; they also provide information to the Air Force (DOD/AF) and DHS to facilitate their mission of protecting the U.S. from hostile aircraft. DOD/AF also owns airfield terminal radars and additional surveillance assets for US perimeter protection. Recently, FAA’s mission has been redirected such that FAA is now only responsible for cooperative aircraft; FAA is therefore pursuing the fielding of an independent non-radar system such as the Automatic Dependent Surveillance-Broadcast (ADS-B) (JPDO, 2005) for tracking cooperative aircraft. The current (or any future) radar aircraft surveillance system will then become only a secondary or emergency backup system for FAA. Detection and tracking of non-cooperative aircraft would become a DHS and DOD/AF mission. FAA recently turned over responsibility for the cost of operation and maintenance of the long-range aircraft surveillance radars to DOD/AF and DHS.
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Evaluation of the Multifunction Phased Array Radar Planning Process The JAG/PARP report notes a number of potential additional uses of Multifunction Phased Array Radar (MPAR): detection and tracking of airborne toxic releases and volcanic ash; measurement of fine-scale winds in support of fire suppression and evacuation, air quality assessment, or tracking of low-level toxic releases; detection and tracking of birds; and accurate typing and tracking of precipitation for hydrology, mudslide prediction, and agriculture. All of these potential uses are deemed possible for MPAR technology; however, in most cases they would represent the most stressing requirements for a radar system, either in higher sensitivity or in greatly increased coverage (such as low-level coverage in mountainous areas for fire suppression support). Furthermore, these capabilities do not yet fully exist. Consequently, the owners, users and beneficiaries of such capabilities are not yet fully identified. These groups must be adequately identified before they can define requirements. LIMITATIONS OF THE CURRENT RADAR NETWORK One of the primary drivers of any future weather and aircraft surveillance system should be the limitations in the ability of the current system to meet existing surveillance requirements. Some of the limitations of the current system, such as the lack of dual polarization, high radar maintenance costs and inadequate radar system networking, have been acknowledged and are being addressed. However, a number of studies have demonstrated significant limitations that are not being addressed with current radar acquisition or upgrade programs. Looking specifically at weather surveillance requirements, a variety of limitations of the current WSR-88D radar network have been identified. The WSR-88D has proven to be particularly important for hydrological applications. With the current single-polarization design, estimates of radar reflectivity factor Z are used with empirical Z-R relationships (where R designates rainfall rate) to perform Quantitative Precipitation Estimation (QPE). Unfortunately, these relationships are notoriously inaccurate and highly dependent on storm type, season, and location. As a result, hydrologists almost always use rain gauges as ground-truth sensors to adjust the radar estimates of rainfall rate. This process is cumbersome and costly, and severely limits the coverage over which rainfall can be estimated accurately and economically. Dual-polarization radar techniques have emerged as the most promising remote sensing technology for obtaining more accurate QPE. In addition, hydrometeor classification can be accomplished with these types of radars (e.g., Ryzhkov et al. 2005). Because of the potential value of dual polarization, the NWS has embarked on an extensive upgrade to the entire network of WSR-88D radars to polarimetric capabilities. Maintaining this capability would be required for any future national weather radar network. A primary limitation is the inability of any radar network comprising widely spaced long-range radars to provide comprehensive low-altitude coverage (eg, at altitudes below 1-2 km). In the mountainous Western United States, flood prediction, hydroelectric power management, agriculture and fire detection and suppression efforts depend critically on accurate assessment of precipitation amounts. Westrick et al. (1999) examined the ability of the current radar network to provide QPE in the West and determined that radar now detects as little as one quarter of the precipitation falling in
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Evaluation of the Multifunction Phased Array Radar Planning Process many regions, and greatly misrepresents precipitation type. Addressing this shortfall in the current weather surveillance network could be particularly stressing for the development of a replacement system. An NRC study carried out for the FHWA (NRC, 2004) identified a serious deficiency in defining low-level precipitation for road traffic management. Better radar observation of the planetary boundary layer could provide fine-scale winds for air quality and tracking toxics or smoke, support to fire suppression efforts, and better detection of clear-air wind events. To observe the fine-scale winds and non-precipitating cloud bases mentioned in the JAG/PARP report and to meet requirements for sensing low-level precipitation, this serious coverage deficiency would need to be addressed. The current WSR-88D data update interval of over four minutes has been identified as a significant limitation for tornado and severe hail prediction. Examples (such as Vasiloff, 2001) have shown that more frequent updates can greatly improve the detection and proper interpretation of tornadic precursors, leading to enhanced warning lead times. Better assimilation of radar information into mesoscale numerical weather prediction (NWP) systems can also increase tornado warning lead times. This will require treating radar information as part of an integrated prediction system, instead of a standalone sensor. The concept of integrating sensors and NWP into networked systems for rapid response again raises ownership issues. NOAA/NWS has ownership of most continental U.S. NWP. The FAA does execute some processing and warning algorithms using data from their radar systems, but model predictions beyond a few minutes are the responsibility of the NWS. Under a recent agreement with DOD, NOAA/NWS provides all operational continental US mesoscale NWP, with the exception of coastal regions and possible classified operations. NOAA/NWS is proceeding with efforts to acquire and assimilate radar information into NWP systems. However, to date this has not been a driver for radar systems acquisition. Identification of limitations of the current aircraft surveillance network is clearer, as stated in the Strategy for Homeland Defense and Civil Support (DOD, 2005). Limitations are primarily in the areas of update interval (less than four seconds desired) and coverage (contiguous coverage desired of all US states, territories, borders and surrounding waters at 3000 ft and higher above ground level, extending 600 nmi beyond the boundaries.) The Strategy report specifically highlights limitations in low-level radar coverage and sensitivity. While the coverage limitation is simple to state, increasing radar coverage to meet such aircraft surveillance requirements would be stressing (see also Chapter 8). The need for very rapid updates also highlights the question of multitasking weather and aircraft surveillance, and the issue will have to be examined carefully. Only by acknowledging the limitations of the current radar networks can a realistic cost-benefit study be performed, or realistic development programs proceed. The JAG/PARP report highlights a study by Weber et al. (2005; also 2007) which identifies substantial budgetary benefit in replacing the current systems with a future MPAR system—while only meeting current capabilities. This study may obfuscate the true cost of upgrading the existing network to only meet current requirements.
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Evaluation of the Multifunction Phased Array Radar Planning Process NEEDS VERSUS RESEARCH The JAG/PARP report highlights the requirements for weather and aircraft surveillance as well as the potential for additional capabilities that could possibly be provided by MPAR technology. It lays out a Research and Development (R&D) plan to explore an MPAR architecture and additional capabilities that an MPAR system could provide. However, this can only be considered exploratory research of a promising technology. In order to achieve a focused R&D effort leading to a proposal for a replacement weather and aircraft surveillance system, specific program management criteria must be met. These are (broadly): An agency or multi-agency agreement of ownership of the future system. A multi-agency agreement of interest (acknowledgement as a user or clear beneficiary) and willingness to work with the owner(s) to establish requirements and budgetary support. The development of nominal system architecture to meet expected US and US territory weather and aircraft surveillance requirements, which will allow meaningful cost-benefit tradeoffs and drive a focused radar, networking and communications R&D effort.