Measurements and Retrievals from a New 183GHz Water Vapor Radiometer in the Arctic M'P' Cadeddu1, J'

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Measurements and Retrievals from a New 183-GHz
Water Vapor Radiometer in the ArcticM.P.
Cadeddu1, J.C. Liljegren1 and A.
Pazmany21Argonne National Laboratory, Argonne,
IL2Prosensing, Inc., Amherst, MA
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• Overview of the instrument
• Data analysis
• Retrieval algorithm
• Retrieval results
• Conclusions

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Instrument

• SBIR Phase II prototype
• Deployment in Barrow 4/14/2005
• Successful data stream collection and processing

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Instrument
GVR Design

• 4 double side-band channels at 1, 3, 7, 14 GHz
  from 183.3 GHz
• Bandwidth 0.4, 1.0, 1.4, 2.0 GHz
• Measurement Rate 4/minute including calibration

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Instrument
Data

• One year of operation has been useful to
• Investigate RFI interference.
• Identify hardware-related issues.
• Check quality of calibration.
• Assess data quality.
• Based on the operations of the past year, the
  instrument will be sent back to Prosensing Inc.
  this summer for improvement of initial prototype.

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Data
Comparison of measured (lines) and modeled
(squares) brightness temperatures in January.
TBGVR-TbmonoRTM mean and SD (clear sky N31)
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Clear-sky brightness temperature measured by the
GVR (top) and MWR (bottom).
Data
Retrieval
Cloudy measurements
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Retrieval
Gauss-Newton method Find a maximum probability
state by finding the zero of the gradient of the
cost function J
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Retrieval
xa, Sa, E
x0(1)0.05 x0(i)RH from MWRP T(i) T from
MWRP y(j) from GVR
Radiative transfer model MonoRTM

yn, K(i,j) xn1
Check convergence
no
Convergence criteria xn1(1) - xn(1) lt
?1 xn1(i) - xn(i) lt ?2 i2,27
yes
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Retrieval

• PWV (p) is computed from RH profile by using the
  MWRP-provided temperature profile.
• Total retrieval error covariance

Error in x Smoothing error Forward model
error Retrieval Noise. Sx SOSN SN
Sx-1KTE-1KSx
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Retrieval
Results
Assuming Gaussian error pdf
Covariance of retrieved PWV (Sp)
Estimated retrieval error ?PWV 0.1 mm ?LWP
0.006 mm
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Results
GVR and MWR retrievals of LWP (top) and PWV
(middle) for two weeks in January.
PWV measured by radiosonde and retrieved (N47
cases).
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Results

• Difference between retrieved and measured PWV as
  a function of measured PWV.

Less spread in GVR data LWPlt3mm
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Results

• Retrieved LWP distribution during clear sky
  (IRT?224 K) in January 2006 (N499).

Lower SD during clear sky
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CONCLUSIONS

• Instrument working for the past year. Several
  hardware/ RFI problems identified during trial
  period.
• Satisfactory agreement with MonoRTM model.
• Estimated PWV accuracy0.1 mm (PWVlt3mm).
• Clear case LWP distribution ?0.004 mm, SD
  0.002 mm.
• Data available from the Archives!