reference quality upper-air measurements: gruan data
TRANSCRIPT
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
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
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
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
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
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
Parameterisation of sensor response
∆
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
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
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
Temperature: uncertainties
GRUAN RS92 data product CIMO TECO 27-30 September 2016 www.gruan.org
Dominant uncertainty:Sensor orientation wrt Sun
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
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
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
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
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
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
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)