Castillo, Tyler

Chronis, Themis

Collis, Scott

Hein, Paul

Helmus, Jonathan

Hoover, Kacie

Lang, Timothy

NASA Technical Reports Server

 Statistical evaluation of three distinct automated Doppler dealiasing algorithms  
using a hand-dealiased shipborne radar dataset 
Timothy Lang, Paul Hein, Themis Chronis, Tyler Castillo, Kacie Hoover, Scott Collis, Jonathan Helmus 
Contact Info: Timothy Lang, NASA MSFC (ZP11), 
Huntsville, AL 35812; (256) 961-7861, timothy.j.lang@nasa.gov 
Funding for this work has come from NASA CYGNSS and OVWST 
1. Introduction 3. Results 
Initiate 
Terminate 
T. Ashcraft 
We seek an effective, open-source, automated Doppler dealiasing 
tool for processing a large number of radar volumes, in order to 
ingest these data into single- or multi-Doppler retrieval algorithms, as 
well as into model data assimilation schemes. 
 
The Python Atmospheric Radiation Measurement (ARM) Radar 
Toolkit (Py-ART) provides three automated dealiasing methods. 
Evaluation of their performance is required. For this we use the hand-
dealiased NASA TOGA C-band radar dataset from the Dynamics of 
the Madden-Julian Oscillation campaign (DYNAMO). 
Example of Manual Dealiasing in Solo3 
4. Summary and Conclusions 
•  Performance of all three algorithms is very high when volumes are significantly aliased 
(~1000s of folded gates) 
•  Algorithms may not be worth running if few folds – “Critical mass” of folds needed? 
•  On average, 4DD performs very similarly to hand-dealiasing, but failures during individual 
radar volumes can and do occur 
•  Region-Based and Phase-Unwrap methods perform worse than 4DD, but are good 
options if 4DD fails. Phase has higher POD and CSI but also higher FAR than Region. 
•  Region and Phase methods prone to occasional massive failures (CSI ~0) 
Reflectivity Folded Unfolded 
TOGA Doppler velocity data  
•  Hand-dealiased using NCAR Solo3 
•  One volume every 30 minutes over Cruises 2-4 
•  360-deg PPI volumes, normally 22 tilts apiece 
•  Exclude INU failures, other major radar problems 
 
Py-ART Version 1.5 (Helmus et al., Poster Session 1)  
•  pyart.correct.dealias_region_based (REGION) 
o  Regions of similar velocities identified and unfolded 
against each other by modeling system as a 
dynamic weighted graph 
o  interval_splits=3, skip_between_rays=100 
•  pyart.correct.dealias_unwrap_phase (PHASE) 
o  Multi-dimensional phase unfolding method originally 
designed to analyze optical fringe-patterns 
o  unwrap_unit=‘volume’, keep_original=False 
•  pyart.correct.dealias_fourdd (4DD) 
o  James and Houze (2001), six-step process that 
uses sounding and previous scan info to correct 
o  In present study, previous unfolded radar volume 
used as sounding, not radiosonde 
Statistical Analysis 
•  Performance evaluated against manually dealiased 
field (assumed 99% accuracy) 
•  Python simplifies analysis via dicts and logical masks 
•  Hit = Correctly dealiased, Miss = Not, False Alarm = 
Unnecessary dealiasing 
•  Probability of Detection (POD), False Alarm Rate 
(FAR), Critical Skill Index (CSI)  
2. Methodology 
Cruise 3 
•  Cruise 3 results shown here – Increasing CSI with increasing number of folds 
•  Cruise 4 results (not shown) similar to Cruise 3 
•  Cruise 2 results still being analyzed and debugged – Region-Based failed A LOT. 
Phase 
Hand 
Region 
Original 
4DD 
Phase 
Hand 
Region 
Original 
4DD 
Lo
w
 T
ilt
 
H
ig
h 
Ti
lt 
E
xa
m
pl
e 
fro
m
 1
1/
24
/1
1,
 C
S
I =
 0
.9
95
 (4
D
D
), 
0.
98
1 
(R
eg
io
n)
, 0
.9
44
 (P
ha
se
) 
•  Binary behavior (esp. Phase); 
algorithms did extremely well 
or bombed. 
•  Failures common when few 
folds, Phase and Region 
sometimes w/ many folds 
Time Series               
of CSI & Folds                     Scatterplots – Hit vs. Miss vs. FA 
Method Velocity Median Absolute 
Error (m s-1) 
Mean Square 
Error (m2 s-2) 
4DD Radial 0.22 0.42 
Tangential 0.23 0.73 
Region Radial 0.28 0.71 
Tangential 0.33 0.82 
Phase Radial 0.29 3.39 
Tangential 0.56 1.51 
None Radial 12.6 293 
Tangential 13.3 269 
4DD 
Effects on Single-Doppler Retrievals 
(See Talk 12B.2, 4:45p, 11/17) 
Results for 11/24/11, 1200 UTC 
Hand 
Median POD, 
FAR, CSI as 
functions of 
folded gates 
threshold 
CSI for 4DD, 
Region, Phase 
vs. number of 
folded gates 
Zoomed for small 
numbers of 
folded gates 
Cruise 3 
https://ntrs.nasa.gov/search.jsp?R=20150018444 2019-08-31T06:30:01+00:00Z


Statistical Evaluation of Three Distinct Automated Doppler Dealiasing Algorithms Using a Hand-Dealiased Shipborne Radar Dataset

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