from real-time to final data — some thoughts on quality control rolf bütikofer, erwin o....
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From real-time to final data — Some thoughts on quality control
Rolf Bütikofer, Erwin O. FlückigerUniversity of Bern, Switzerland
Measurements at NM Station
• Time tag
• NM count rate
• Atmospheric pressure
• Temperature, rel. humidity, wind speed ...
• Observation of snow accumulation on and around detector housing
Time Tag
• Accuracy of clock (mechanical clock, clock with quartz oscillator, radio clock, GPS, time server)
• Time shift of clock
• Local time, UT, winter/summer time
• Start or end of interval
NM Count Rates (1)• Electronic problems:
– Power cut– Rel. humidity (condensation leakage current
spurious counts)– Stability of HV power supply– Temperature effects on electronic components– Drifts in power supply, amplifier and discriminator– Static charging– Change in counter tube characteristics (broken
counters)– Replacement of counter tubes, amplifier
NM Count Rates (2)
• Environment: – Change in material close to the NM (detector
housing)– Relocation of NM– Accumulation of snow on roof or around
detector housing
Atmospheric Pressure Measurements
• Effects of winds on atmospheric pressure measurements: gusty and high wind speeds
• Drift of barometer
Bern Cosmic Ray GroupUniversity of Bern, Switzerland operates 3 NMs:
• 18-IGY NM at Jungfraujoch, 3570 m asl, since 1958
• 3-NM64 NM at Jungfraujoch, 3475 m asl, since 1986
• Special Neutron Monitor at Bern, 570 m asl, since 1977
Main interest of Bern group:
• Analysis of solar cosmic ray events (GLEs)
• Analysis of Forbush decreases
• Space Weather
18-IGY Neutron Monitor Jungfraujoch
Roof of Sphinx building
IGY NM
3-NM64 Neutron Monitor Jungfraujoch
Roof of Research Station
IGY
NM64
Jungfraujoch
Special Neutron Monitor BernRoof of Physics Institute, University of Bern
Effects of wind on pressure measurements
• Gusty winds cause short-time fluctuations
• Strong winds cause diminished readings of conventional barometers
Bernoulli effect: pmeas = peff – ρv2/2
1-minute pressure data
NM count rate
atmospheric pressure
wind speed
Snow Effect
Precipitation
Meteo station at Interlaken, 18 km NNW from Jungfraujoch
mm/hour
CEST (UTC+2)
Count rate vs. Snow Accumulation on Roof
NM64: ~1% / 10 cm snow
First preliminary results
ΔNIGY vs. Snow Thickness
~0.5% / 10 cm snow
~0.2% / 10 cm snow
NM Operating Only Part of Interval
Only Part of Monitor Operating
Normalisation Factors
• One section of NM not in operation
• Change in number of counter tubes
• Change in NM type IGY NM64
• Significant change in the environment of NM (change of detector housing, moving NM)
Scaling factors
Monthly Graph
Monthly Data
YYYY MM DD HHMM Uncorr Press Corr ******************************************* 2007 2 1 100 5244/ 492.7 5808.8/ 2007 2 1 200 0 492.7 0.0 2007 2 1 300 5252/ 492.7 5818.2/ 2007 2 1 400 5256 492.6 5818.4 2007 2 1 500 5264 492.5 5825.1 2007 2 1 600 5257 492.5 5813.6 2007 2 1 700 5239 492.6 5801.4 2007 2 1 800 5252 492.8 5824.8 2007 2 1 900 5250 492.8 5825.3 2007 2 1 1000 5242 493.0 5825.2 2007 2 1 1100 5263- 493.1 5856.5- 2007 2 1 1200 5251 493.3 5850.9 2007 2 1 1300 5222 493.5 5830.3
Conclusions
• Automatic data processing is OK for real-time data, however data must be controlled carefully by operators of NM before publishing final data
• For preparation of final data corrections of measurements can be made for some effects, wheras some effects should only be mentioned with a comment in final dataset
• Postprocessing of NM data within database by cross-correlation with nearby NM stations is possible
Effect of Atmosphere
• Change in air mass has large effect on count rate
• This change is the only significant meteoro-logical factor
• Barometric pressure is used as a proxy for the air mass
• Barometric pressure coefficient ~1 % / mmHg→ pressure must be measured very accurately
Cosmic Rays in the Atmosphere
Principle of Neutron Monitor•Reflector (Paraffin/Polyethylen)•Producer (Lead)•Moderator (Paraffin/Polyethylen)•Counter Tube (B10F3)
B10 + n → Li7 + α
NM Simulation with Monte Carlo
• Simulation of interactions of neutrons with material (detector housing, detector, ground, snow)
• Simulation of detection of slow neutrons in the counter tubes
• Geant4 software package
Detector and material in the environment
Snow on the roof
Roof (copper, wood)
Snow around detector housing
Ground (concrete)
NM64 neutron monitor
View from top
Visualisation of particle interactions