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Goddard Airborne Radar Activities for Studies of Precipitation and Clouds

Goddard Airborne Radar Activities for Studies of Precipitation and Clouds. Gerald Heymsfield and Robert Meneghini. Science Rationale for Doppler Radars on High-altitude Aircraft.

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Goddard Airborne Radar Activities for Studies of Precipitation and Clouds

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  1. Goddard Airborne Radar Activities for Studies of Precipitation and Clouds Gerald Heymsfield and Robert Meneghini

  2. Science Rationale for Doppler Radars on High-altitude Aircraft • They provide measurements of weather phenomena and associated rainfall with higher resolution than possible from spaceborne or surface-based measurements. • They can be used as test bed for new hardware techniques to improve satellite rain algorithms (TRMM, GPM). • Doppler radars provide important information on both the precipitation structure and the dynamics of precipitation and clouds through profiled vertical motion measurements.

  3. Mapping of EDOP and CRS Measurements Into Code Y Strategic Plan • EDOP and CRS through process studies (field campaigns) and new technology development provide information toward the following questions: • What are the effects of clouds and surface hydrologic processes on earth’s climate? • How can weather forecast duration and reliability be improved by new space-based observations, data assimilation, and modeling? • How are global precipitation, evaporation, and the cycling of water changing?

  4. Goddard Airborne Radars • ER-2 Doppler Radar (EDOP) • 9.6 GHz Doppler precipitation radar • Effective for studying convection, hurricanes, etc. • Developed at GSFC and flown since 1993 • Measures vertical structure of precipitation and 2-D winds • ER-2 Cloud Radar System (CRS) • 94 GHz Doppler radar developed at GSFC and under SBIR • Highly sensitive radar for cirrus and atmospheric radiation studies • Will fly soon for CRYSTAL and can provide CloudSat validation for high-altitude cirrus clouds • Measures vertical structure of clouds and vertical motions

  5. nadir 20 pointing • • • • • • • • beam Vectors are • • • • • • • combined to • • • obtain vert. V f hydrometeor V n • • • • • • • motions and • along-track winds 10 HEIGHT (KM) • • • • • • • • forward pointing • • • • • • • • beam 37.5 m • • • • • • • • 100 m 0 TIME, DISTANCE ER-2 Doppler Radar (EDOP) • Precipitation X-band (9.6 GHz) Doppler radar located in nose of NASA ER-2 high-altitude aircraft emulates satellite view • Dual-fixed antennas for nadir and forward views along aircraft track • Forward and nadir beam measure intensity and air motions in precipitation region • Forward beam provides dual polarization capability for micro- physical characterization of precipitation (liquid, snow, hail)

  6. EDOP Example Hurricane Humberto 2001(CAMEX-4)

  7. Development Work in Progress • Cloud Radar System • Heymsfield, CRS completion for ER-2 flights during CRYSTAL (NRA funded) • Required significant in-house integration • Differential-frequency techniques for radar • Meneghini and Bidwell, FY2001 DDF • Approach applied to EDOP ground-based measurements with 1 GHz frequency difference • IIP proposal written in 2001 but not funded. • Not proposed but promising: Use of closely spaced freqencies (1 MHz separation) for Doppler radar measurements from space.

  8. Differential-frequency Doppler Radar(DDF funding FY2001) • Basic Idea • Measure dual-wavelength Doppler data with a single broad-band antenna & transmitter/receiver • availability of power amplifier is a critical technological item • require broad-band antenna with well-matched patterns • small differential signal levels require large # of samples • Useful meteorological information can be gathered by proper choice of frequencies • Ka-band frequencies with 7%-10% separation • information can be used to estimate: • rain rate, liquid water content, particle phase state • characteristics of the snow & rain size distributions • vertical speed of hydrometeors & air motion

  9. Goddard Engineering Expertise • Both EDOP and CRS have involved annually about 1 MY of microwave engineering support from the Microwave Instrument Technology Branch (Code 555) • CRS has involved low-level support from Code 567 for antenna testing, as well as guidance from other Code 500 groups on technical issues. • The support for the CRS development and for EDOP calibration and improvements has been lower than required, necessitating contractor engineering support. • Most of the engineering effort has be used for developing field deployable ER-2 radars rather than development of new technologies such as the differential frequency radar concept.

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