NASA and the National Center for Atmospheric Research have developed an icing remote sensing technology that has demonstrated skill at detecting and classifying icing hazards in a vertical column above an instrumented ground station. This technology has recently been extended to provide volumetric coverage surrounding an airport. Building on the existing vertical pointing system, the new method for providing volumetric coverage will utilize a vertical pointing cloud radar, a multifrequency microwave radiometer with azimuth and elevation pointing, and a NEXRAD radar. The new terminal area icing remote sensing system processes the data streams from these instruments to derive temperature, liquid water content, and cloud droplet size for each examined point in space. These data are then combined to ultimately provide icing hazard classification along defined approach paths into an airport

King, Michael

Reehorst, Andrew

Serke, Dave

NASA Technical Reports Server

National Aeronautics and Space Administration!
www.nasa.gov 
Preliminary Findings of Inflight Icing Field Test to 
support Icing Remote Sensing Technology Assessment 
1 
Prepared by: 
 
Michael King & Andy Reehorst 
National Aeronautics and Space Administration, Glenn Research Center 
 
Dave Serke 
National Center for Atmospheric Research, Research Applications Laboratory 
 
June 22-25, 2015 
 
https://ntrs.nasa.gov/search.jsp?R=20150019752 2019-08-31T06:06:11+00:00Z
National Aeronautics and Space Administration!
www.nasa.gov 
Presentation Overview 
•  Background 
•  Icing remote sensing systems 
–  NASA Icing Remote Sensing System 
–  NASA Terminal Area Icing Remote Sensing System 
•  In-situ atmospheric sounding systems 
–  Weather Balloon Systems 
–  Anasphere SLWC Sensor 
–  SLWC Calculation  
•  Selected winter 2015 system comparisons 
–  Forecasting and Release Decision Criteria 
–  March 17, 2015 
–  March 20, 2015 
–  March 26, 2015 
•  Summary 
2 
National Aeronautics and Space Administration!
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Background 
•  Icing accidents continue to occur despite advances in all aspects of icing 
related technologies  
•  The spatial and temporal variability of icing severity is a major challenge to 
providing pilots and controllers with actionable icing hazard information 
•  The need for direct detection and measurement of hazardous icing 
conditions is still significant despite improvements to weather models over 
the past decade 
•  NASA has teamed with NCAR for the last 10 years to develop a ground-
based remote icing hazard detection algorithm test bed to address this 
need 
•  The result of this effort is the NASA Icing Remote Sensing System 
(NIRSS) 
•  NASA carried out a weather balloon campaign during winter 2015 using a 
new supercooled liquid water (SLWC) sensor to generate the database 
necessary to validate NIRSS 
3 
National Aeronautics and Space Administration!
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•  The NIRSS remotely detects hazardous icing conditions using ground 
based meteorological instrumentation 
–  Vertical icing condition severity product is derived from calculated supercooled liquid 
water content estimated by the NIRSS algorithm 
–  Includes 3 vertically pointing instruments: a Radiometrics Radiometer, a Vaisala 
Ceilometer and a METEK Ka-Band Cloud Radar System 
–  System shown to agree well with the Aviation Weather Center (AWC) Current Icing 
Product (CIP) and Pilot Reports (PIREP) 
•  Johnston, Christopher J., et al., “Comparison of In-Situ, Model and                                                                                                       
Ground Based In-Flight Icing Severity”, NASA/TM—2011-217141,                                                                                                                 
Dec. 2011 
•  An acknowledged shortcoming of NIRSS                                                    
is that it only produces a vertical profile                                                            
of the icing conditions 
–  To help fully protect a terminal area and                                                                        
provide information that accounts for the                                                                           
temporal and spatial variability of icing                                                                          
conditions, a volumetric remote measurement                                                            
capability is required 
Icing Remote Sensing Systems: 
NASA Icing Remote Sensing System (NIRSS) 
4 
Reehorst & Serke, “A Terminal Area Icing Remote Sensing System”, 
NASA/TM-2014-218417, Nov 2014 
radiometer 
ceilometer 
radar 
National Aeronautics and Space Administration!
www.nasa.gov 
Icing Remote Sensing Systems: 
NASA Terminal Area Icing Remote Sensing System 
•  The terminal area system was developed to 
address the shortcomings of NIRSS 
–  Produces icing condition severity classification along 
defined airport approach and departure paths every 
minute based on most recent measurements 
–  Icing hazard is output in 9 boxes centered along  
each runway approach path, from the airport center 
to 25 Km out 
•  Terminal Area System builds upon the 
existing capability of NIRSS 
–  Includes NIRSS instrumentation, an additional point-
able radiometer and ingests NEXRAD radar data 
–  In addition to NIRSS vertical condition fields, the 
system ingests : 
•  Radiometer slant elevation ILW measurements along 
airport runway headings 
•  NEXRAD reflectivity and ground surface wind data to 
advect the measured fields into the 3-D volume 
5 
Reehorst & Serke, “A Terminal Area Icing Remote 
Sensing System”, NASA/TM-2014-218417, Nov 2014 
Radiometrics Radiometer on top of IRT roof with 
NEXRAD radar and KCLE airport in background 
radiometer 
NEXRAD 
National Aeronautics and Space Administration!
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•  Weather balloons used to obtain in-situ measurements characterizing 
conditions aloft 
–  Instrument package carried specialized, disposable sensor to measure supercooled 
liquid water content in addition to standard meteorological radiosonde 
•  Weather balloon operations were carried out from the NASA Glenn 
Research Center hangar ramp 
–  Balloon release location is 0.25 Km from ground                                             
instrumentation and within 1 Km of airport center 
–  Coordination with Cleveland Hopkins Airport Air                                                         
Traffic Control established to ensure safe                                                               
operations 
•  24 instrumented balloons released for 12                                                   
different icing events between Jan. 22 and                                                
Apr. 23, 2015 
Instrument Package: InterMet iMet-1-RSNB Radiosonde 
and Anasphere SLWC Sensor 
In-situ Atmospheric Sounding Systems: 
Weather Balloon Systems 
6 
National Aeronautics and Space Administration!
www.nasa.gov 
In-situ Atmospheric Sounding Systems: 
Supercooled Water Content Sensor 
•  Balloon-borne SLWC sensor 
–  Anasphere, Inc., through a NASA contract, developed a new, prototype sensor based on 
work by Hill and Woffinden  
•  Hill & Woffinden, “A Balloon-borne Instrument for the Measurement of Vertical Profiles of 
Supercooled Liquid Water Concentration,” Journal of Applied Meteorology, 1980 
•  Measurement principle is based on the reduction in natural vibration 
frequency of a wire due to ice accretion 
–  Natural frequency decreases with increasing ice accretion along the wire 
–  SLWC is calculated using time history                                                                                
of natural frequency 
•  Frequency measurements obtained                                                            
every 3 seconds, nominally 
–  Wire is periodically perturbed by magnet                                                                 
attached to a servomotor 
–  Natural vibration frequency determined                                                                         
using Fast Fourier Transform  
7 
Anasphere, Inc. SLWC Sensor: Wire Vibration Video Loop 
National Aeronautics and Space Administration!
www.nasa.gov 
SLWC Calculation 
•  SLWC is calculated using the frequency 
profile 
–  The time derivative of the frequency, df/dt, is the 
driving term 
–  The coefficient C is model, assumption specific 
–  The terms ε, D and ω are collection efficiency, 
wire diameter and ascent speed, respectively 
•  Outliers in the frequency are removed and 
the profile is smoothed prior to calculation 
–  Robust local regression using weighted linear 
least squares and a second degree polynomial 
(Matlab: LOESS) 
8 
400
500
600
700
800
900
1000
1050
Pr
es
su
re
[m
ba
r]
41 42 43 44 45
7.2
5.6
4.2
3.0
1.9
1.0
0.1
 
Frequency
[Hz]
Pr
es
su
re
 A
ltit
ud
e
[K
m
]
March 17, 2015, Balloon 002 frequency profile showing characteristic 
frequency depression due to ice accretion on wire 
SLWC = C
εDω
df
dt
General form of the equation to calculate SLWC from Hill, “Analysis of 
Supercooled Liquid Water Measurements Using Microwave Radiometer 
and Vibrating Wire Devices,” J. Atmo. & Oceanic Tec., Vol. 6, 1989. 
National Aeronautics and Space Administration!
www.nasa.gov 
Case Studies: 
Forecasting and Release Decision Criteria 
•  Long-Range Forecast 
–  Long-range icing forecasting was provided by NCAR  
•  Weather systems of interest identified in advance  
•  Next-Day Forecast 
–  NCAR provided next-day forecast specifying period of interest 
•  Notice to Airmen (NOTAM) submitted for forecast specified period of time 
•  Coordination with NASA GRC Hangar personnel  
•  Short-Range Forecast 
–  Coordination with NCAR on conditions during period of interest for release 
decision 
–  Radiometer-derived ILW used as final release decision criterion 
•  ILW > 0.3mm 
–  Coordination with Cleveland Air Traffic Control for permission to release 
•  Class B Airspace 
9 
National Aeronautics and Space Administration!
www.nasa.gov 
Case Studies: 
March 17, 2015 (Remote Sensing and PIREP) 
Aircraft 
Type 
Time 
[UTC] 
Flight Level 
[Ft] 
Icing 
Report 
1 E145 1423 5200-6000 Light Clear 
2 B712 1520 4000 Light Rime 
3 B712 1552 4000 Mod. Rime 
10 
NIRSS icing severity product output for March 17, 2015  
[Note: Markers only indicate corresponding time and altitude and do not represent transection of aircraft with the NIRSS sample volume] 
PIREP Map for March 17, 2015 
 
PIREP Summary for March 17, 2015 for period of interest 
1 2 3 
National Aeronautics and Space Administration!
www.nasa.gov 
−20 −10 0 10 20
400
500
600
700
800
900
1000
1050
Temperature
[°C]
Pr
es
su
re
[m
ba
r]
Iso
the
rm
s (
°C
)
0
−1
0
−2
0
−3
0
−4
0
Dry Adiabats (°C)
40
30
20
10
0
−10
Saturation Adiabats (°C)1612
8
4
0
−4
−8−12
−16
Sa
tu
ra
tio
n 
M
ixi
ng
 R
at
io 
(g
/K
g)
10
5
2
1
 
 
T−NIRSS
DP−NIRSS
T−Sonde
DP−Sonde
41 42 43 44 45
Frequency
[Hz]
 
 
Frequency
Outliers
0 0.25 0.5 0.75 1 1.25 1.5
7.2
5.6
4.2
3.0
1.9
1.0
0.1
 
SLWC
[g/m3]
Pr
es
su
re
 A
ltit
ud
e
[K
m
]
 
 
NIRSS
Sonde
ILW−NIRSS = 0.63
ILW−Sonde = 0.58
Case Studies: 
March 17, 2015 Balloon 002 (Comparison) 
11 
ILW = 1
ρ(H2O)liq
SLWCdz
z0
z
∫
Skew-T, Log-P Diagram (left), Frequency Profile (middle), and SLWC Profile (right) for March 17, 2015, 1447 UTC  
National Aeronautics and Space Administration!
www.nasa.gov 
Case Studies: 
March 20, 2015 (Remote Sensing & PIREP) 
•  No icing PIREPs were issued within 90 Km of CLE during the 
period of interest (1300 to 1800 UTC) on March 20, 2015 
12 
NIRSS icing severity product output for March 20, 2015 
National Aeronautics and Space Administration!
www.nasa.gov 
Case Studies: 
March 20, 2015 Balloon 001 (Comparison) 
13 
Skew-T, Log-P Diagram (left), Frequency Profile (middle), and SLWC Profile (right) for March 20, 2015, 1500 UTC 
−20 −10 0 10 20
400
500
600
700
800
900
1000
1050
Temperature
[°C]
Pr
es
su
re
[m
ba
r]
Iso
the
rm
s (
°C
)
0
−1
0
−2
0
−3
0
−4
0
Dry Adiabats (°C)
40
30
20
10
0
−10
Saturation Adiabats (°C)1612
8
4
0
−4
−8−12
−16
Sa
tu
ra
tio
n 
M
ixi
ng
 R
at
io 
(g
/K
g)
10
5
2
1
 
 
T−NIRSS
DP−NIRSS
T−Sonde
DP−Sonde
42 43 44 45
Frequency
[Hz]
 
 
Frequency
0 0.2 0.4 0.6 0.8
7.2
5.6
4.2
3.0
1.9
1.0
0.1
 
SLWC
[g/m3]
Pr
es
su
re
 A
ltit
ud
e
[K
m
]
 
 
NIRSS
Sonde
ILW−NIRSS = 0.27
ILW−Sonde = 0.25
National Aeronautics and Space Administration!
www.nasa.gov 
Case Studies: 
March 26, 2015 (Remote Sensing and PIREP) 
•  Junk Case 
14 
NIRSS icing severity product output for March 26, 2015  
[Note: Markers only indicate corresponding time and altitude and do not represent transection of aircraft with the NIRSS sample volume] 
PIREP Map for March 26, 2015 
Aircraft 
Type 
Time 
[UTC] 
Flight Level 
[Ft] Icing Report 
1 E145 1428 12000 No Icing  Below 12000 Ft 
2 E145 1439 13000 Mod. Rime 
3 C525 1650 14000 Light Rime 
4 C56X 1836 10500 No Icing 
5 C510 1910 15500 Light Mixed 
PIREP Summary for March 26, 2015 for period of interest 
1 2 
3 4 5 
National Aeronautics and Space Administration!
www.nasa.gov 
Case Studies: 
March 26, 2015 Balloon 003 (Comparison) 
15 
Skew-T, Log-P Diagram (left), Frequency Profile (middle), and SLWC Profile (right) for March 26, 2015, 1659 UTC  
−20 −10 0 10 20
400
500
600
700
800
900
1000
1050
Temperature
[°C]
Pr
es
su
re
[m
ba
r]
Iso
the
rm
s (
°C
)
0
−1
0
−2
0
−3
0
−4
0
Dry Adiabats (°C)
40
30
20
10
0
−10
Saturation Adiabats (°C)1612
8
4
0
−4
−8−12
−16
Sa
tu
ra
tio
n 
M
ixi
ng
 R
at
io 
(g
/K
g)
10
5
2
1
 
 
T−NIRSS
DP−NIRSS
T−Sonde
DP−Sonde
42 43 44 45
Frequency
[Hz]
 
 
Frequency
Outliers
0 0.2 0.4 0.6 0.8
7.2
5.6
4.2
3.0
1.9
1.0
0.1
 
SLWC
[g/m3]
Pr
es
su
re
 A
ltit
ud
e
[K
m
]
 
 
NIRSS
Sonde
ILW−NIRSS = 0.89
ILW−Sonde = 0.37
National Aeronautics and Space Administration!
www.nasa.gov 
Summary 
•  A successful weather balloon campaign utilizing a new SLWC 
sensor was conducted out of NASA Glenn Research Center 
from Jan. 22 to Apr. 23, 2015 
–  A database of 24 balloon soundings for 12 different icing weather events 
was generated that can be used to validate and improve the NIRSS and 
Terminal Area Systems 
•  Initial results between the remote sensing and in-situ systems 
show agreement in several cases 
–  The altitude of significant SLWC and general distribution SLWC aloft agree 
in several cases 
–  The ILW between NIRSS and the weather balloon soundings agree in 
several cases 
–  Disagreement between NIRSS and the weather balloons system may be 
attributed to spatial and temporal sampling differences 
16 


Preliminary Findings of Inflight Icing Field Test to Support Icing Remote Sensing Technology Assessment

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