Liquid Water Path from Chilbolton Radiometers

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Liquid Water Path from Chilbolton Radiometers
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Chilbolton radiometers pointing atzenith via
reflector plate angled at 45o

22.2, 28.8 37.5 GHZ radiometers
2.3 degree beamwidth
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Radiometer Processing Steps

• Calibration of RCRU radiometers is performed
  using absorber held at temperature of liquid
  nitrogen. Calibration is not performed through
  the receiving antennas
• Additional correction has now been applied to
  measured sky brightness temperatures to account
  for the additional loss in the antenna lenses.
• Loss in Rx antennas
• 22GHz is 0.172dB / 28GHz is 0.091dB /
  37GHz is 0.24dB
• Algorithm to estimate liquid water path, and
  total integrated water vapour, from the corrected
  sky brightness temperatures is applied to 22 28
  GHz values, and to the 22 37 GHz values.
  Algorithm coefficients based on analysis of
  multiple radiosonde ascents
• Levels of integrated water vapour path are
  compared with values derived from radiosonde
  ascents made at Larkhill 35km to the West

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Example of stratoculus cloud observed on 19th
June 2003 during CWAVE03 at Chilbolton

• Subsequent slides show
• Cloud field observed at zenith during the day.
• Period from 1050 to 1505 showed total
  cloud cover at zenith
• 
  (Field of view is 60 degrees by 45 degrees)
• 94 GHz radar reflectivity
• IR ceilometer backscatter
• Two retrievals of liquid water path estimated
  from brightness temperature measurements at 22.2,
  28.8 and 37.6 GHz

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Cloud Cover at Chilbolton on 19th June 2003
405 UT 420 435 450
505 520 535
550 605 620 635
650 705 720
735 750 805 820
835 850 905
920 935 950 1005
1020 1035 1050
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Cloud Cover at Chilbolton on 19th June 2003
1505 UT 1520 1535 1550
1605 1620 1635
1650 1705 1720 1735
1750 1805 1820
1835 1850 1905 1920
1935 1950 2005
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• 94 GHz radar reflectivity

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• Attenuated backscatter coefficient

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• Liquid water path for 19th June 2003

LWP retrieval error estimated at /-
0.025 Kg/m2
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• Liquid water path for 19th June 2003

LWP retrieval error estimated at /-
0.025 Kg/m2
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Summary

• Reliable calibration procedure for Chilbolton
  radiometers has been established performed at
  least once per week.
• Correction for loss due to lens in radiometer
  horn antenna has been included in processing
  procedure.
• We have shown data collected during the CWAVE03
  campaign at Chilbolton in June 2003 to illustrate
  the liquid water path retrieval capability.
• The small differences between outputs from the
  two retrieval procedures requires further study.
• Estimation of zenith path loss at 94 GHz is now
  possible.