vhf atmospheric and meteor radar installation at davis, antarctica

VHF ATMOSPHERIC AND METEOR RADAR INSTALLATION ATDAVIS, ANTARCTICA: PRELIMINARY OBSERVATIONSR. J. Morris 1 , D. J. Murphy 1 , I. M. Reid 2 , and R. A. Vincent 21 Australian Antarctic Division, Kingston 7050, Tasmania, Australia2 University of Adelaide, Adelaide 5005, South Australia, AustraliaIntroductionA 55 MHz VHF atmospheric radar was commissioned at the high-latitude station Davis(78.0°E, 68.6°S geographic; 74.6°S magnetic), Antarctica during the austral summer of 2002-03. This paper presents an overview of this new facility which has been constructed for theAntarctic environment including, the 12 x 12 array of Yagi antennas, equipment module, andassociated infrastructure. Several aspects of the design tailored for the harsh Antarcticconditions are described. The radar specifications as developed by Atmospheric RadarSystems will be given together with an account of the proposed science to be conductedutilizing this new facility. The radar commenced 'spaced antenna' mode observation with 20kW of transmitted power from mid February 2003, and is scheduled to be upgraded to 120kW of transmitted power and a beam steering capability from November 2003. Some initialtroposphere and stratosphere region wind observations are presented. The facility includes ameteor radar capability and some preliminary mesosphere region results are also presented.Scientific ObjectivesVHF radars have been used extensively and successfully in the northern hemisphere to studythe dynamics of the Earth's polar atmosphere, however, with the exception of a short-termexperiment at South Georgia, they have not been used in the southern polar-regions. VHFradars allow the measurement of wind speeds in the troposphere and lower stratospherethroughout the year and in the mesosphere during daylight hours. They collect data with ahigh-time resolution (typically every few minutes) and with high-spatial resolution (typicalaltitude ranges of a few hundred metres) and operate stand alone with little operatorintervention. As a result, they have played a key role in developing our understanding of theenergy source regions in the lower atmosphere, energy deposition regions higher up, thecoupling between them and the resulting global circulation.The potential of the VHF radar can be demonstrated through consideration of the followingscientific objectives.Investigations of troposphere, stratosphere and mesosphere dynamics:• Gravity waves; climatology; case studies; propagation studies; and estimates ofmomentum flux in these atmospheric regions• Turbulence• MeteorologyStudies of Polar Mesospheric Summer Echoes (PMSEs):• Interhemispheric differences• Morphology and climatology• Links to noctilucent clouds• TheoryMeteor studies:• Mesosphere temperatures and winds

A detailed account of the science objectives can be found at www.aad.gov.au under AASProject 2325 "VHF radar studies of the Antarctic mesosphere, stratosphere and troposphere"Drs Ray Morris, Damian Murphy, Andrew Klekociuk, Gary Burns, Iain Reid and BobVincent.VHF Radar SpecificationsArray dimensions: 42.43 m x 42.43 mAntennas: 3 element Yagi's with a folded dipole driver elementAntenna Grouping: Groups of four adjacent antennas are grouped to form 36 sub-arraysTranceiver: 6 channel fixed frequencyMeteor Capability: The radar can be switched to a 5 antenna meteor array (with a separatetransmit antenna)Table 1. Description of the Davis VHF Radar.Frequency55 MHzArray12x12 grid of 3-element Yagi antennas 0.7 Lambda spacingEffective Area of Array 2180 m 2 At 55 MHzOne-way beam width ~ 7 degrees Using whole arrayPeak Power 20 kW (2003) 120 kW (2004) In 6 x 20 kW modulesAverage Power 6 kW 5% Duty cyclePower Aperture Product ~1.5 x 10 7 Wm 2 At peak powerFigure 1. A photograph of the Davis VHF radar installation.Antenna Array Design and ConstructionThe project was assessed under a ‘preliminary environmental assessment’ in compliance withthe Madrid Protocol for Protection of the Antarctic Environment. Final site selection was

ased upon a geotechnical engineering assessment to protect the array from possible damagedue to permafrost and annual freeze and thaw cycles. The 3-element Yagi antennas that makeup the array were attached to their vertical 50 mm diameter support posts at varying heightsabove the ground so as to set the plane of their driver elements horizontal. The posts ranged inlength from 2 to 4 metres. The posts were supported at their base by concrete blocks designedto prevent translation and rotation. The strain caused by wind loading on the antennas andposts was taken up by a system of guy ropes. Concrete blocks were placed on small pads ofun-reinforced concrete approximately 800 mm x 800 mm x 250 mm. These provided an evensurface to support the blocks and were oversized to allow the block to be moved into thecorrect position on the pad. The guy system consisted of a network of ropes at the height ofthe top of the poles. After tensioning, the guy ropes were secured to anchor points at the endsof each row and column of antennas. After setting each support post to vertical, the top ofeach post was clamped to an East-West and a North-South aligned guy. The rope used was a‘braid’ made of fibre that has a high strength and a low stretch factor. The radar module haspower and fibre optics communications to the main station network.Radar Operating Schedule for the 2003 Austral Winter with Preliminary ObservationsFigure 2. Horizontal windmeasurements in themesosphere and lowerthermosphere obtained withthe VHF radar operating inmeteor mode.Through the Antarctic winter, the VHF radar schedule emphasises detection of meteor echoesfrom the mesosphere and lower thermosphere. These echoes are to be used, in conjunctionwith other instruments at Davis, for wind and temperature comparisons. However, soundingsof the lower atmosphere are carried out every 12 minutes. The frequency and duration oflower atmospheric soundings was later increased to every 6 minutes for two hour intervalsfollowing ozone-sonde and standard sonde balloon releases.Figure 3. Direction ofarrival for meteordetections on 30 April2003 at Davis.

Figure 4. Horizontal velocitiesin the troposphere and lowerstratosphere obtained using theDavis VHF radar. One minutelower atmosphere soundings arecarried out at 12 minuteintervals.Figure 5. Average echo powerand signal-to-noise ratio fortropospheric soundings usingthe Davis VHF radar.Davis Station Research FacilityThe VHF Radar is located on the shoreline of Heidemann Bay some 2 km from Davis station,Antarctica (78.0°E, 68.6°S geographic; 74.6°S magnetic). The Australian Antarctic Divisionand the Australian physics community have developed Davis as their primary site for highlatitudemiddle and upper atmospheric physics research. Finally, the science objectives will beaddressed using the suite of instruments at Davis coupled with international collaboration.Middle atmospheric experiments include:Rayleigh and Doppler lidar; 2 MHz Medium Frequency Spaced Antenna radar; Czerny-Turner Spectrometer observing OH airglow; Fast Fourier Transform Spectrometer observingOH airglow; Scanning Radiometer; and UV Spectrophotometer.Upper atmospheric experiments include:Fabry-Perot Spectrometer; Digital Portable Sounder; Three Field Photometer; Wide AngleTwo Field Photometer; Fluxgate Magnetometer; Induction Magnetometer; IRIS ImagingRiometer; 30 MHz Standard Riometer; All Sky Video Camera; Ionospheric Scintillations;Total Electron Content; and Magnetic Absolutes.AcknowledgmentsWe acknowledge the support of the Australian National Antarctic Research Expeditions (ANARE)expeditioners at Davis during the 2002-03 austral summer. The VHF radar was installed by Space andAtmosphere Science expeditioners – Damian Murphy, Ray Morris, Lloyd Symons, Danny Ratcliffeand Richard Groncki, and Trade expeditioners – Paul Saxby, Alan Taylor and Chris Heath, under thesupervision of Janine Lea. Richard Groncki provided the photograph of the VHF radar at Davis.