Introducing VESPA-22: a ground- based microwave spectrometer for measuring middle atmospheric water vapour at polar latitudes 27 April 2012 EGU General Assembly April 2012 EGU General Assembly 2012 Pietro Paolo Bertagnolio, Giovanni Muscari, Irene Fiorucci and Massimo Mari Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy Department of Earth Sciences, University of Siena Distributed under Creative Commons Attribution 3.0 Creative Commons Attribution 3.0Creative Commons Attribution 3.0 Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy Department of Earth Sciences, University of Siena Distributed under Creative Commons Attribution 3.0 Creative Commons Attribution 3.0Creative Commons Attribution 3.0

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 1/14 Our goal To observe changes in the water vapour concentration profile in the stratosphere and mesosphere in the polar regions Long-term (decadal trends) Short-term (diurnal cycle) With a new ground-based microwave spectrometer to measure the GHz transition of water vapour as part of the NDACC network

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 2/14 Main ideas Balancing technique (signal-reference) Front-end: –Parabolic reflector –Uncooled heterodyne receiver –chopper with dielectric sheet –Wobbler for λ/4 shift Back-end: –Acqiris FFT spectrometer Calibration: –Noise diodes for on-line calibration –LN2 for absolute calibration

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 3/14 Observation goalsInstrument specifications Observation angle 10°-15°Spectral resolution (B) 61 kHz Signal-to-noise ratio (SNR) 115Spectrometer bandwidth 1 GHz Total integration time (ttot) 12 hrs (1 h if binned) Antenna beamwidth (HPBW) 3.5° Altitude range of profiles kmEffective observation time (t / ttot) 40% Profile accuracy15%System temperature (Tsys) 165 K

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 4/14 Functional scheme

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 5/14 VESPA-22 (water Vapor Emission Spectrometer for Polar Atmospheres at 22 GHz)

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 6/14

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 7/14 Parabolic antenna Feedhorn from University of Navarra –Same design as IMK Karlsruhe –Length: 20 cm –HPBW: 12.5° Parabolic reflector from Thomas Keating Ltd. –Our design –Long axis: 60 cm –Total HPBW: 3.5°

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 8/14 Radiation pattern Half-Power Beam Width (HPBW) = 3.5° Sidelobes < -40 dB below main lobe Cross-polarization < -24 dB below main polarization

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 9/14 Diagrammi di radiazione e fase fra 21.2 e 23.2 GHz Campo lontano (4 m) Antenna + specchio parabolico Campo vicino (0.43 m) Antenna

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 10/14 Chopper mirror With small absorber bar With dielectric (DELRIN) sheet

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 11/14 Chopper performance Dielectric materialBalancing angleAdded power wrt zenith Plexiglas43° Small absorber bar Delrin (2 mm)28.8°10.2% Delrin (5 mm)8.5% Delrin (2+2 mm)43°5.2%

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 12/14 Wobbler performance

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 13/14 Setup di test 13 LNA Amplifier2IF MixerTo Back-end Antenna Amplifier LO 1IF LO 2IF 1IF Mixer Sideband filter IF filters

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 14/14 Noise diode calibration Cold body (LN2)Calibration sources Hot body

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 15/14 Noise diode calibration Trec = 312 K

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 16/14 No baseline subtracted

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 17/14 2 sine waves subtracted

EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – EGU G ENERAL A SSEMBLY 2012 – 27/04/2012 P IETRO P AOLO B ERTAGNOLIO – 18/14 Future work (now the fun starts…) Improve baseline flatness: –λ/4 wobbler instead of fixed shift –Delrin compensating sheet –Front-end optimization Improve sensitivity and Trec –Test single-sideband mixer Test with longer integration times from an high-altitude observatory (Gran Sasso) Set up inversion algorithm Conclusions Long-term monitoring of polar stratospheric water vapour is needed We designed and built a new 22-GHz spectrometer for polar observations We measured the first atmospheric spectra (first light) Long-term monitoring of polar stratospheric water vapour is needed We designed and built a new 22-GHz spectrometer for polar observations We measured the first atmospheric spectra (first light)