reference quality upper-air measurements: gruan data
TRANSCRIPT
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Reference quality upper-air measurements: GRUAN data processing for the Vaisala RS92
radiosonde
Ruud Dirksen, Michael Sommer, Franz Immler, Dale Hurst, Rigel Kivi, Holger Vömel
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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Introduction
• Globally: 800 radiosoundings/day
High-res profiles of important ECVs (PTU, wind)
• Climate research requires reference quality data
Requirements for reference data (Keynote presentation G. Bodeker, Tuesday)
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
GCOS Reference Upper Air Network (2008)
• Traceability to an SI unit
• Uncertainty analysis
• Raw + meta-data
• Documentation
• Validation
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GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
Establishing reference quality
Best estimate+
Uncertainty
Uncertainty of input data
Traceable sensor
calibration
Transparent processing algorithm
Disregarded systematic effects
Black box software
Proprietary methods
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GRUAN data product for RS92
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
Good performance, employed at 50% of GRUAN sitesVaisala calibration of PTU sensors traceable to SI standards
Proprietary algorithms
• Characterization & correction of instrument errors/biases• Vertically resolved error estimates• Well-documented
Error sources for: Temperature HumidityRadiation
Sensor time-lag
Calibration
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Vaisala RS92 radiosonde
• PTU, wind
• 0-35km
• Interval: 1 s
• Ascend rate 5 m/s
• 2 RH sensors, alternate heating
• Capacitive sensors (T, U)
• Reflective, hydrophobic coating
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
T-sensor
GPS
RH-sensors
P-sensor
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Radiation error: Laboratory experiments
Shadow RS92 records background temperature & ambient pressure
Simultaneous testing of 3 radiosondes
p=[3 hPa , ambient]
Difference illuminated – background radiosonde
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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Parameterisation of sensor response
∆
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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Radiation error correction model
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
cloud
cloud
Actinic flux on sensor
• LUT actinic flux
• Streamer model, I+D
• Clear sky & cloudy
• Mid-lat atmosphere
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T-correction profile
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
In processing: average of Vaisalaand GRUAN correction• Update in version 3
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Temperature: uncertainties
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
Dominant uncertainty:Sensor orientation wrt Sun
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RS92 dual soundingA
ltitu
de [k
m]
Night (N=17) Day (N=29)
Estimated uncertainty vs observed differences
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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RH: Dry biases
Heating of humidity sensor
• ∆T: radiation correction of T-sensor
• f: enhancement factor [6, 13] (laboratory experiments)
Uncertainties: ∆T, f
Temperature-dependent dry bias (-30, -70°C)
Based on RS92 - CFH comparison (empirical)
Max at 7% at -60°C (similar to Voemel, 2007)
Uncertainty: comparable to correction
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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RH: sensor time-lag
Low-pass filter
Flattens features in humidity profile
Relevant below -40°C (tropopause)
Correction: numeric inversion + a-posteriori filtering
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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RH: corrections & uncertainties
Dominant uncertainties:•Calibration•Cal. correction•Dry bias
IPW: ~4%
RS92: reliable RH profiles up to UTLS
Yangjiang 20 July 2010
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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Manufacturer’s ground check
RS92 recalibration at 0%RH.
Quality of desiccant
Introduces bias
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
Lindenberg
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Ground check in SHC
• Traceability• 4% change over ~9
years• SHC readings enter
uncertainty budget• Future: use SHC to
scale profile
Lindenberg
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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Outlook
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
• Improve radiation correction
• Redesign architecture processing software (modular, versatile)
• Develop GRUAN data products for other radiosondes
• Change management RS92-RS41 transition P1(11)