Rapid Variations in Atmospheric Refractivity Revealed by an SBand Phased Array Weather Radar

1
Rapid Variations in Atmospheric Refractivity
Revealed by an S-Band Phased Array Weather Radar

• R. D. Palmer1, B. L. Cheong1, T.-Y. Yu2, and C.
  Curtis3
• 1School of Meteorology, The University of
  Oklahoma
• 2School of Computer and Electrical Engineering,
  The University of Oklahoma
• 3Cooperative Institute of Mesoscale
  Meteorological Studies (CIMMS), and NOAA/OAR
  National Severe Storms Laboratory

Supported by NOAA/NSSL under cooperative
agreement NA17RJ1227
http//arrc.ou.edu/
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Overview

• Introduction to the National Weather Radar
  Testbed in Norman, Oklahoma
• Theoretical Background of Refractivity Retrieval
  From Clutter and Overview of OUs Refractivity
  Retrieval Algorithm
• Initial Measurements Using the Phased Array Radar
  (PAR) and Validation Using Scanning Radar and
  Surface Stations

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National Weather Radar Testbed NWRT

• Centerpiece of NWRT is the Phased Array Radar
  (PAR), which is an S-band, klystron-based radar
  using a SPY-1A phased array antenna
• NOAAs National Severe Storms Laboratory (NSSL)
  operates the PAR on the North Campus of the
  University of Oklahoma
• Major goal is to improve severe storm warning
  lead time using phased array radar
• Provide rapid update data for assimilation into
  numerical models
• The NWRT provides a location for
  testing/validation of advanced weather radar
  processing algorithms
• Ultimately, the goal is to perform multi-function
  tasks including weather surveillance, aircraft
  tracking, etc.

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Phased Array Radar (PAR) Design

• Passive array of 4,352 elements
• S-band transmitter (3.2 GHz)
• 1.5-2.1 degree beamwidth over 45 degrees

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Phased Array Radar (PAR)
USAs first research facility dedicated to phased
array radar meteorology
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Overview

• Introduction to the National Weather Radar
  Testbed in Norman, Oklahoma
• Theoretical Background of Refractivity Retrieval
  From Clutter and Overview of OUs Refractivity
  Retrieval Algorithm
• Initial Measurements Using the Phased Array Radar
  (PAR) and Validation Using Scanning Radar and
  Surface Stations

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Refractivity and EM Waves

• Refractive index n
• Near the earth surface, n 1.0003
• Refractivity

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Refractivity, Moisture, and Temperature

• Refractivity
• p air pressure
• T air temperature
• e vapor pressure

• N changes dominated by e

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Refractivity and EM Waves

• Travel time changes with refractive index
• Refractive index is translated into radar phase
• Radar phase from stationary ground clutter
  (constant r) should be constant if refractivity
  remains unchanged

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Example Phase Measurements

• Can we measure refractive index by using radar
  phase?
• Use phase difference from multiple ground targets
  along same radial for range resolution.
• For S-band radars, the phase wraps very quickly
  with increasing range (every 5cm!)

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Phase Difference to Refractivity

• With ?ref and nref measured from a day with
  homogeneous refractivity

Fabry et al., On the extraction of near-surface
index of refraction using radar phase
measurements from ground targets, JTech, 14,
978-987, 1997
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Overview of OUs Refractivity Retrieval Algorithm
Phase measurement for a map of reference phase
Phase measurement during operational time
A map of Phase Difference ??
Image Processing Clutter Quality, Masking,
Smoothing
Radial gradient ? ?N
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Overview

• Introduction to the National Weather Radar
  Testbed in Norman, Oklahoma
• Theoretical Background of Refractivity Retrieval
  From Clutter and Overview of OUs Refractivity
  Retrieval Algorithm
• Initial Measurements Using the Phased Array Radar
  (PAR) and Validation Using Scanning Radar and
  Surface Stations

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Case 1 Monitoring of Large-Scale Temporal
Variations in Refractivity July 12, 2005,
1510-1610 UTC
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Case 2 Rapid Variations of Refractivity During
a Dust StormSept 28, 2005, 1859-1944 UTC
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Comparison Between KOUN and PAR
PAR Refractivity
KOUN Refractivity
Different Radars and Different Algorithms
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Oklahoma MesonetRefractivity and Refractivity
Change
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PAR/Mesonet Comparison
10-minute temporal spacing
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High temporal resolution

• 5-minute temporal spacing

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Conclusions

• Provided introduction to the PAR and the NWRT in
  Norman, Oklahoma, USA
• Reviewed theory of the measurement of surface
  refractivity (moisture) from ground clutter
  signals
• Described processing steps necessary for
  implementation
• Preliminary results from PAR provided and
  compared to near-operational KOUN radar and
  Mesonet surface stations