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Calibrating measurements of precipitable water vapour
F. Kerber et al.
European Southern Observatory at Site 2010 Kislovodsk


Collaboration


University of Lethbridge, Canada
­ R. Querel, D. Naylor, G. Tompkins

U. Valparaiso

­ A. ChacÑn, O. Cuevas, M. Cure, L. Cortes, M. Caneo, L. Illanes ­ J. ThomasOsip, G. Prieto ­ A. OtÀrola, M. SchÆck, T. Travouillon ­ R. Hanuschik, M. Sarazin, C. Guirao, G. Avila, G. Lo Curto, I. Saviane, A. Pizarro, G. Ihle, J. Navarette, A. Smette, D. Rabanus
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GMT, Las Campanas TMT ESO

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Outline


PWV why & how EELT site testing Goals Archival data reconstructing the past PWV campaigns what we have learned Results
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Atmospheric Water Vapour


Precipitable water vapour (PWV)
­ ­ ­ ­

column of atmospheric water [mm] crucial for atmospheric opacity in IR Longterm: site quality Shortterm: operational issue

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EELT site testing


PWV is one factor for site selection Better understand atmospheric PWV
­ Variability ­ Calibrate measurements



La Silla & Paranal wellestablished sites Report to Site Selection Advisory Committee
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Goals:






Reconstruct Record of Precipitable Water Vapour (PWV) over Paranal & La Silla Correlate with satellite data to establish Paranal & La Silla as reference sites for E ELT site evaluation Evaluate merit of methods for operational use at observatory
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Reconstructing the PWV History


La Silla Paranal
­ UVES & FEROS



Standard Star Observations
­ ­ ­ ­ ­ White dwarfs featureless spectrum Taken every UVES night; ~1200 observations useable Time coverage: 20002009 Wide slit: 5/10 arcsec UVES reprocessing with master calibration files
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Atmosphere Model: PWV


Atmospheric model BTRAM (Univ. Lethbridge)

­ HITRAN (2008) ­ Multilayer atmospheric radiative transfer model ­ Midlatitude profile modified with sitespecific archival radiosonde data from Antofagasta ­ 580980 nm, >1000 lines ­ Validated at LCO with MIKE observations ­ Comparison with IRMA (Querel et al. 2008)

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Atmospheric Model: PWV
H2O only, PWV = 1 mm

All other constituents: CO2, O2
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Paranal: wet & dry

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Satellite Data


GOES
­ Time resolution 1 every 3 h, 24 h a day ­ Spatial resolution 12 by 12 km (3 pixel binning) ­ Brightness at 6.5 & 10.7 m clear nights only



ENVISAT
­ Time resolution 1 every 23 days, daytime ­ MERIS: Spatial resolution 1 by 1 km ­ Spectrum: 890900 nm

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UVES archival Data

Paranal

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PWV site statistics
Paranal Median PWV [ mm]
2.1 ± 0.3 (2.2) 2.4 ± 0.5 (1.8) 2.7 ± 0.3 (2.0)

< 1 mm < 1.5 mm [%] [%]
13.5 4.8 1.5 32 18.9 7.9

< 2 mm [%]
47.3 38 29

UVES GOES MERIS

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PWV site statistics
La Silla Median PWV [ mm]
3.4 ± 0.4 (2.4) 5.9 ± 0.6 (2.5) 3.6 ± 0.5 (2.3)

< 1 mm < 1.5 mm [%] [%]
3.3 0.02 0.8 9.2 0.4 11.2

< 2 mm [%]
18.4 1.8 20

FEROS GOES MERIS

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PWV Campaigns
Jul/Aug & Nov 2009

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PWV Campaigns in technical time


Paranal:
­ ­ ­ ­ ­ UVES 700 nm (~950 spectra, cadence 3060s) BACHES 700 nm (140 spectra, 1530 min) CRIRES 5050 nm (110 spectra) VISIR 19.5 m (65 spectra) IRMAs 20 m (~700 h, cadence sec)



Radiosonde balloon launches (U Valparaiso)
­ 11.5 h, 2025 km altitude ­ ~70 launches (La Silla, Paranal)

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Radiosondes

A. ChacÑn et al. (U. Valparaiso)
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Radiosonde Profiles

Temperature Dew Point

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PWV over La Silla Paranal: Status

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Paranal vs Armazones

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IR M A

C R IR E S

UVES
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V IS IR
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Radiosonde vs GOES

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Results


Median PWV over La Silla Paranal EELT site evaluation
­ Paranal 2.4 mm ­ La Silla 3.7 mm ­ Armazones 2.1 mm (OtÀrola et al. 2010: 2.9 mm)



Validated various methods with respect to radiosondes
­ 700 nm 20 m ­ 520%; 0.25/0.5 mm



Remote sensing data (satellites) usable for statistical analysis only, ok for site evaluation 29


Next Steps


Complete analysis (typical time scale of variability) Monitoring at Paranal:
­ http://www.eso.org/qc/GENERAL/PWV/HEALTH/trend _report_ambient_PWV_HC.html ­ http://www.eso.org/sci/facilities/paranal/sciops/CALISTA /pwv/data.html



VISIR upgrade includes PWV PWV forecasting using WRF model (U. Valparaiso)
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PWV Time dependence


IRMA 10 days PWV typical time constant is hours

T. Travouillon
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PWV Time dependence

A. OtÀrola
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PWV Time dependence

A. OtÀrola
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VISIR upgrade project


VISIR: midIR imager & spectrograph at VLT
­ 10 m (Nband) & 20 m (Qband)



VLT: Visitor/service mode: ~50/50 split Optimise use of low PWV Standalone high time resolution monitor PWV as userdefined constraint

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VISIR upgrade project


Science benefit for demanding observations
­ ­ ­ ­ ­ imaging of faint sources in Q, highprecision photometry, spectroscopy of H2 00 S(1) at 17.02 µm, imaging and spectroscopy in Nband < 8 µm, detection of water vapour in circumstellar disks
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Next Steps


PWV as operational tool

VISIR: 712%

­ Standalone monitor on Paranal VISIR upgrade ­ Constraint for SM observations

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Summary Goals met


History of PWV over La Silla & Paranal reconstructed from archival data Paranal as reference site for Northern Chile Feedback to Site selection process Merit for Observatory operations

­ Monitoring with high accuracy feasible ­ PWV crucial tool for scheduling of service mode
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Summary Future


PWV monitor: Standalone, high time resolution, high accuracy VISIR: Observing constraint service mode Benefit to other instrument (CRIRES, MIDI, ISAAC, ...) Comprehensive atmospheric monitoring essential part of infrastructure for EELT
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Courtesy:Wor3dle.net 9