Rain Masking

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Chilbolton Facilities for Atmospheric and Radio
Research
Rain Masking A note on Capacitative Rain
Sensors John Goddard
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Chilbolton Facilities for Atmospheric and Radio
Research

• Investigation into use of simple rain detectors
  to flag onset and cessation of rain
• Valuable for quality control of radar vertical
  profiling
• Comparison of sensors was described at 3rd
  Cloudnet meeting
• Included
• tipping bucket raingauges
• drop counting raingauges
• disdrometers
• optical sensors
• Conclusions were
• Distrometer and Optical gauge - both good
  indicators of precipitation onset
• Drop counting gauges lag these by 2-5 minutes
• (maybe depending on how wet the collector has
  remained since the last event)
• Tipping bucket gauge - not useful for this
  purpose
• - lags of tens of minutes in weak
  precipitation
• - 2 factors, collector wetting and bucket
  capacity

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Chilbolton Facilities for Atmospheric and Radio
Research

• Action 3.1 from the meeting was to investigate
  capacitative sensors
• may be cost effective solution?
• Two types of capacitative sensor have been
  deployed at Chilbolton
• primarily to assist rain data quality control
• eliminating calibration spikes, etc
• Vaisala DRD11A Rain Detector
• Sontay WD-RS Rain sensor

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Chilbolton Facilities for Atmospheric and Radio
Research
DRD11A Rain Detector
WD-RS Rain Sensor
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Chilbolton Facilities for Atmospheric and Radio
Research
DRD11A deployed

• Both instruments have heated surfaces
• eliminates fog and dew
• reduces effects of snow
• (not tested at Chilbolton yet!)
• Both instruments use ttl voltage levels
• (0 or 5V for rain/no rain)
• DRD11A has additional delay circuitry giving 2
  minute interval between drops before setting the
  no rain state
• DRD11A interface was straight forward
• WD-RS required additional interface circuit

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Chilbolton Facilities for Atmospheric and Radio
Research
Example from 1 October 2003
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Chilbolton Facilities for Atmospheric and Radio
Research
Expanded view
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Chilbolton Facilities for Atmospheric and Radio
Research
End of the event
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Chilbolton Facilities for Atmospheric and Radio
Research
Blip
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Chilbolton Facilities for Atmospheric and Radio
Research

• Conclusions
• Instruments have similar characteristics
• DRD11A is easier to install
• it is appears to be more sensitive
  (over-sensitive?)
• WD-RS sensor costs 170
• (www.sontay.com)
• DRD11A sensor costs 740
• (www.vaisala.com)