Comparisons of optical flow winds with observed radial velocity from KTOP radar


Robert Rabin(1,2)

Chris Velden, Dave Stettner, Steve Wanzong(2)

NOAA/NSSL(1) and UW-Madison/CIMSS(2)


BACKGROUND

In order to compare the winds estimated from the optical flow technique with the Doppler radar wind observations, the following steps were performed.

1. The optical flow technique was applied to sets of two sequential radar reflectivity images from the lowest elevation tilt (0.5 degrees).  The time difference between images is approximately 1.5 to 2 minutes during the SAILS scanning mode utilized by NEXRAD WSR-88D radars in this case. The images are from Level-III radar products obtained from the NOAA NCEI. The data were remapped to an equal latitude/longitude projection on a1000x1000 point grid with 0.5 degree resolution. The McIDAS-X software was used for remapping and display of the images..

2. The displacements obtained from the optical flow technique were used to estimate u,v wind components at each grid point.

3. The radial wind components with respect to the viewing angle of the KTOP radar were computed from the optical flow winds.

4. The observed radial wind component from the WSR-88D radar can then be compared directly with the output of step #3.

Examples:

28 May 2019 (times in UTC)
Radial wind component from Optical flow derived winds
Yellow: 0 to50 m/s
Cyan: -50 to 0 m/s		 Observed radial wind component from Doppler radar
Yellow: 0 to50 m/s
Cyan: -50 to 0 m/s		 Observed - Optical Flow
Red: -10 to 0 m/s
Green: 0 to 10 m/s
23:01:29 23:01:29
 23:01:29
23:02:48 23:02:48 23:02:48
23:04:22 23:04:22 23:04:22
23:06:01 23:06:01 23:06:01
23:08:04 23:08:04 23:08:04
23:09:28 23:09:28 23:09:28
23:11:08 23:11:08 23:11:08
23:55:07 23:55:07 23:55:07


The general patterns of radial velocity appear similar in depicting the southwesterly flow. However, there is a consistent error in the optical flow winds in some locations, such as the positive difference just northeast of the radar and negative difference to the southeast. The error could be caused by wind shear in the vertical and the geometry of radar scans which slope with range from the radar. 

    

HTML5 based applications used for interactive animations were developed by Tom Whittaker of the Space Science and Engineering Center  SSEC, University of Wisconsin-Madison.  The animations can take a while to load, depending on network speed, computer systems, etc.

  Disclaimer. The products from GOES or other satellites shown here are experimental. These have been generated within a research environment and are not intended to be considered operational. Timeliness, availability, and accuracy are sought but not guaranteed.

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