Air Traffic Management Concept Baseline Definition - The Boeing ...
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Air Traffic Management Concept Baseline Definition - The Boeing ... Air Traffic Management Concept Baseline Definition - The Boeing ...

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Systems (AWOS). These systems are complementary, but perform somewhat different functions. The ASOS was intended to be a complete surface meteorological observing station that would replace human observers. ASOS systems are deployed at airports but also in a much broader weather observing network around the country. Problems have emerged with some of the ASOS sensors, particularly the visibility package, which have prevented the ASOS from achieving the goal to eliminate human observers. Work continues on these problems, but the likelihood of their success is not known at this time. Human observations of some critical aviation impact variables will likely be needed for the foreseeable future (National Research Council, 1995). The AWOS is designed strictly as a terminal weather information system. It was not intended to eliminate human observers, but it does provide certified observations of ceiling, visibility, altimeter setting, wind speed, and wind direction. It too has been criticized for providing misleading aviation weather information, especially ceiling observations. Specific information on the performance of the sensors on the ASOS and AWOS was not available at the time of this writing. However, it is reasonable to expect that the accuracy of the sensors is adequate for most current and expected analytical and modeling applications. The notable exception is that the visibility and present weather sensors have been criticized for giving inaccurate and misleading information under some circumstances (NRC, 1995). An important issue for the success of future improvements in aviation weather information is likely to be increasing the spatial density of measurements to provide improved coverage of key weather parameters. When completed, the ASOS network will consist of over 850 units and the AWOS network will consist of 160 units located at airports that do not otherwise provide certified weather information. (Some state governments have also purchased AWOS systems.) These two surface monitoring systems will likely go forward for a decade or longer as the primary surface observing systems used for aviation weather. Other sources of surface data are used for aviation weather, primarily to support tactical decision making. For example, the FAA operates sensors that measure runway visual range (RVR). Errors in automated RVR systems (and ASOS and AWOS visibility measurements) deployed to date suggest that near term improvements in visibility measurement technologies could improve the efficiency of airport operations. The FAA also operates the LLWAS, a network of tower-mounted anemometers that is supposed to detect potentially hazardous wind shear and microburst conditions at the airport. However, concerns over the efficacy of LLWAS data have sometimes lead controllers to ignore LLWAS warnings. This was apparently the case during the 1994 crash of a USAir MD-80 at Charlotte-Douglas airport (NRC, 1995) during a microburst event. In the near term, improvements in wind shear algorithms and/or the use of more Doppler radar information could improve safety conditions in the terminal area. There is also a national network of lightning detection sensors that show where cloud-to-ground lightning strikes are occurring. 90

ASOS AWOS TDWR NEXRAD Surface Upper-Air Rawin Profiler LLWAS MDCRS Observations ASR-9 Weather Radar Satellite NEXRAD TDWR Figure 5.15 Aviation Weather Observation Function 5.5.1.2 Upper-Air Observations Adequate upper-air meteorological data are critical to the aviation weather system, and this is an area where additional resources and technology development in the near term and far term could produce significant improvements in aviation weather information. The primary source of upper-air data comes from the NWS’s network of rawinsonde observations. Radio wind soundings are made by weather balloons that carry aloft a small instrument package called a radiosonde. The radiosonde measures atmospheric pressure, temperature, and moisture as it ascends, which are used to calculate altitude. Radio direction finding techniques or navaid-based tracking systems follow the motion of the balloon, from which winds aloft are computed. The accuracy of the thermodynamic sensors is generally good (a few percent), while rms errors in winds aloft are typically 1-3 m/s. Sounding systems expected to become available in the near term will use GPS to track balloon position, which should improve the accuracy of altitude data and may significantly improve the quality of upper-air wind information. GPS radiosondes have not yet come into widespread use because of their cost relative to conventional radiosondes, but this situation is expected to improve over the next few years. In the U.S., two soundings are made each day, one at 00 UTC (1900 EST) and the other at 1200 UTC (0700 EST), at approximately 80 stations in the CONUS, Alaska, and Hawaii. The data are used to analyze weather patterns on constant pressure surfaces and aloft winds at constant flight levels, and to initialize NWP models. The meteorological community is virtually unanimous in its opinion that increasing the spatial and temporal density of upper-air data would significantly improve weather forecasts, but due to budget constraints there are no plans to expand the rawinsonde network. The current network is probably just barely adequate to characterize synoptic-scale weather features (fronts, locations of high and low pressure centers, etc.), but much of the weather that affects aviation occurs on the mesoscale, e.g., connective storms. The current rawinsonde 91

ASOS<br />

AWOS<br />

TDWR<br />

NEXRAD<br />

Surface<br />

Upper-<strong>Air</strong><br />

Rawin<br />

Profiler<br />

LLWAS<br />

MDCRS<br />

Observations<br />

ASR-9<br />

Weather<br />

Radar<br />

Satellite<br />

NEXRAD<br />

TDWR<br />

Figure 5.15 Aviation Weather Observation Function<br />

5.5.1.2 Upper-<strong>Air</strong> Observations<br />

Adequate upper-air meteorological data are critical to the aviation weather system, and<br />

this is an area where additional resources and technology development in the near term<br />

and far term could produce significant improvements in aviation weather information. <strong>The</strong><br />

primary source of upper-air data comes from the NWS’s network of rawinsonde<br />

observations. Radio wind soundings are made by weather balloons that carry aloft a small<br />

instrument package called a radiosonde. <strong>The</strong> radiosonde measures atmospheric pressure,<br />

temperature, and moisture as it ascends, which are used to calculate altitude. Radio<br />

direction finding techniques or navaid-based tracking systems follow the motion of the<br />

balloon, from which winds aloft are computed. <strong>The</strong> accuracy of the thermodynamic<br />

sensors is generally good (a few percent), while rms errors in winds aloft are typically 1-3<br />

m/s. Sounding systems expected to become available in the near term will use GPS to<br />

track balloon position, which should improve the accuracy of altitude data and may<br />

significantly improve the quality of upper-air wind information. GPS radiosondes have not<br />

yet come into widespread use because of their cost relative to conventional radiosondes,<br />

but this situation is expected to improve over the next few years.<br />

In the U.S., two soundings are made each day, one at 00 UTC (1900 EST) and the other<br />

at 1200 UTC (0700 EST), at approximately 80 stations in the CONUS, Alaska, and<br />

Hawaii. <strong>The</strong> data are used to analyze weather patterns on constant pressure surfaces and<br />

aloft winds at constant flight levels, and to initialize NWP models. <strong>The</strong> meteorological<br />

community is virtually unanimous in its opinion that increasing the spatial and temporal<br />

density of upper-air data would significantly improve weather forecasts, but due to budget<br />

constraints there are no plans to expand the rawinsonde network. <strong>The</strong> current network is<br />

probably just barely adequate to characterize synoptic-scale weather features (fronts,<br />

locations of high and low pressure centers, etc.), but much of the weather that affects<br />

aviation occurs on the mesoscale, e.g., connective storms. <strong>The</strong> current rawinsonde<br />

91

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