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Introducing VESPA-22: a ground-based microwave spectrometer for measuring middle atmospheric water vapour at polar latitudes. Pietro Paolo Bertagnolio , Giovanni Muscari, Irene Fiorucci and Massimo Mari. 27 April 2012 EGU General Assembly 2012. - PowerPoint PPT Presentation
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Introducing VESPA-22: a ground-based microwave spectrometer for
measuring middle atmospheric water vapour at polar latitudes
27 April 2012EGU General Assembly 2012
Pietro Paolo Bertagnolio, Giovanni Muscari, Irene Fiorucci and Massimo Mari
Istituto Nazionale di Geofisica e Vulcanologia, Rome, ItalyDepartment of Earth Sciences, University of Siena
Distributed under Creative Commons Attribution 3.0
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/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 22.235 GHz transition of water vapour as part of the NDACC network
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Outline
• Stratospheric H2O and its impact on PSCs
• The observational challenges of the 22-GHz H2O line
• How does the technique work?
• Our instrumental setup• First measured and
calibrated spectra• Conclusions and future
work
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Decadal change in stratospheric H2O as yet not well understood
• Steady rise since 1980• 10% decrease in 2000• Influence on surface warming 30%
of GHG from “Contributions of stratospheric water
vapor to decadal changes in the rate of global warming.” S. Solomon et al. – Science - 2010
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Impact of H2O increase on Arctic PSC formation
from “Quantifying Denitrification and Its Effect on Ozone Recovery”, Tabazadeh at al. – Science - 2000
+ 1 ppmvH2O
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
The observational challenge
tropo
strato
meso
thermo
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Balanced Beam-Switching Measurement Technique
Troposphere
CompensatingSheet
Receiver
Stratosphere
Signal beam
𝑻 𝒛∗𝑨𝑺
𝑇 𝑡𝑟𝑜𝑝𝜖𝑡𝑟𝑜𝑝,𝑆
Referencebeam
𝑻 𝒛∗𝑨𝑹
𝑇 𝑡𝑟𝑜𝑝𝜖𝑡𝑟𝑜𝑝 ,𝑅
𝑻 𝒄𝝐𝒄
𝑇 𝑆−𝑇 𝑅=𝑇 𝑧∗ (𝐴𝑆𝛼𝑡𝑟𝑜𝑝 ,𝑆−𝐴𝑅𝛼 𝑡𝑟𝑜𝑝 ,𝑅𝛼𝑐 )
•
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
VESPA-22 (water Vapor Emission Spectrometer for Polar Atmospheres at 22 GHz)
Parabolic mirror
Choppermirror
Quarter-wavelength shift
Receiver
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Parabolic antenna
Half-Power Beam Width (HPBW) = 3.5°Sidelobes < -40 dB below main lobeCross-polarization < -24 dB below main polarization
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Noise diode calibration
Cold body (LN2) Calibration sources
Hot body𝑇 𝑠−𝑇 𝑅=𝐺 (𝑉 𝑠−𝑉 𝑅 )=𝑇𝑁𝐷
𝑉 𝑁𝐷+𝑅−𝑉 𝑅(𝑉 𝑠−𝑉 𝑅)
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
Noise diode calibration
0 5000 10000 150000.5
1
1.5
2
x 108
FFT Channels
FFT
Cou
nts
"Raw" Calibration Spectra
Cold Target (77 K)Hot Target (295 K)Noise Diode 1 (84 K)Noise Diode 2 (131 K)
Trec = 312 K
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
22.15 22.2 22.25 22.3-2000
-1000
0
1000
2000
3000
Frequency [GHz]
Brig
htne
ss T
empe
ratu
re [m
K]
Calibrated Spectrum18-04-2012 13:20-17:20
Effective Integration Time 80'
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
22.225 22.23 22.235 22.24 22.245-100
0
100
200
300
Frequency [GHz]
Brig
htne
ss T
empe
ratu
re [m
K]
Water Vapour Emission Line @ 22.235 GHz18-19/04/2012
Effective Integration Time 3h40'
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/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”)
EGU GENERAL ASSEMBLY 2012 – 27/04/2012PIETRO PAOLO BERTAGNOLIO – [email protected]/14
References• Bertagnolio, P. P., Muscari, G., & Baskaradas, J. (2012). Development of a 22 GHz
ground-based spectrometer for middle atmospheric water vapour monitoring. European Journal of Remote Sensing, 51-61. doi:10.5721/EuJRS20124506
• Solomon, S., Rosenlof, K. H., Portmann, R. W., Daniel, J. S., Davis, S. M., Sanford, T. J., & Plattner, G.-K. (2010). Contributions of stratospheric water vapor to decadal changes in the rate of global warming. Science (New York, N.Y.), 327(5970), 1219-23. doi:10.1126/science.1182488
• Tabazadeh, A., Santee, M. L., Danilin, M. Y., Pumphrey, H. C., Newman, P. A., Hamill, P. J., & Mergenthaler, J. L. (2000). Quantifying Denitrification and Its Effect on Ozone Recovery. Science, 288(5470), 1407-1411. doi:10.1126/science.288.5470.1407
Thank you for your attention!