David J. Serke

National Center for Atmospheric Research, Boulder, Colorado

Paul Beaty

Radiometrics Corporation, Boulder, Colorado

Pat Kennedy

Colorado State University, Fort Collins, Colorado

Frederick Solheim and Randolph Ware

Radiometrics Corporation, Boulder, Colorado

Marcia K. Politovich

National Center for Atmospheric Research, Boulder, Colorado

David Brunkow and Robert Bowie

Colorado State University, Fort Collins, Colorado

A New Narrowbeam, Multi-Frequency 

Scanning Radiometer and Its Application 

to In-Flight Icing Detection

NASA/CR—2010-216357

July 2010
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David J. Serke

National Center for Atmospheric Research, Boulder, Colorado

Paul Beaty

Radiometrics Corporation, Boulder, Colorado

Pat Kennedy

Colorado State University, Fort Collins, Colorado

Frederick Solheim and Randolph Ware

Radiometrics Corporation, Boulder, Colorado

Marcia K. Politovich

National Center for Atmospheric Research, Boulder, Colorado

David Brunkow and Robert Bowie

Colorado State University, Fort Collins, Colorado

A New Narrowbeam, Multi-Frequency 

Scanning Radiometer and Its Application 

to In-Flight Icing Detection

NASA/CR—2010-216357

July 2010

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared under Contract NNC06E046T
Acknowledgments

This research is supported by the NASA Aviation Safety Program, Integrated Intelligent Flight Deck Project. 

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Level of Review: This material has been technically reviewed by NASA technical management.
A New Narrowbeam, Multi-Frequency Scanning Radiometer and Its 

Application to In-Flight Icing Detection 

David J. Serke

National Center for Atmospheric Research 

Boulder, Colorado 80307 

Paul Beaty 

Radiometrics Corporation 

Boulder, Colorado 80301 

Pat Kennedy 

Colorado State University 

Fort Collins, Colorado 80523 

 

Frederick Solheim and Randolph Ware 

Radiometrics Corporation 

Boulder, Colorado 80301 

Marcia K. Politovich 

National Center for Atmospheric Research 

Boulder, Colorado 80307 

David Brunkow and Robert Bowie 

Colorado State University 

Fort Collins, Colorado 80523 

1.0 Introduction

Aircraft accrete ice in flight when the aircraft’s surface 

impacts supercooled liquid water. Accretion often occurs on 

engine intakes or propellers, leading edges of the wings and 

tail fin structures. This in-flight icing can result in significant 

loss of aerodynamic performance due to increased drag, 

change in the effective wing shape and added weight. Loss of 

performance can lead to dangerous aircraft responses that are 

outside of the envelope of normal flight operations. It is an 

ongoing goal in the aviation safety community to be able to 

accurately quantify in time and space, the presence of in-flight 

icing hazards. Since aircraft icing is a process that requires the 

presence of an aircraft to occur, icing cannot be directly 

measured with a remote system. While ideally all aircraft 

would be equipped with icing remote detection equipment to 

provide coverage over their entire flight paths, this is not 

practical. The need to provide a ground-based capability that 

can provide information to all aircraft entering and departing a 

terminal area is a key element in facilitating icing avoidance. 

The current techniques for the remote detection and 

measurement of icing conditions rely on the identification of 

liquid water and then the inference or measurement of the 

surrounding air temperature. The Current Icing Product (CIP), 

developed by the National Center for Atmospheric Research 

(Bernstein et al., 2005), ingests near-realtime Rapid Update 

Cycle model atmospheric and microphysical fields, visible and 

infrared satellite data, surface weather observations, PIlot 

REPorts (PIREPs) and lightning network data to infer liquid 

and subfreezing temperatures aloft. CIP is an operational 

system currently in use by the FAA. Another warning system 

is the NASA Icing Remote Sensing System (NIRSS), which is 

a testbed prototype (Reehorst et al., 2006). It consists of a 

vertically pointing Metek K-band radar to define cloud top and 

base heights and to determine cloud layer structure. There is 

also a Radiometrics Corporation multi-channel radiometer 

(Solheim et al., 1998), whose channels are used to derive 

integrated liquid water and atmospheric temperature profiles. 

A laser ceilometer is also incorporated to further define the 

cloud base. Software integrates the data streams in realtime 

and the derived liquid is distributed within the detected cloud 

layer(s) based on internal logic to arrive at an in-flight icing 

hazard categorization. This testbed system is an effort to 

provide in-flight icing hazard warnings with existing, costeffective technologies and the system is currently positioned 

near John Hopkins Airport at NASA Glenn Research Center in 

Cleveland, Ohio. 

Combining ground-based microwave radiometers with 

radars has shown great promise, but deficiencies with the 

current generation of radiometers have somewhat limited their 

value. These shortcomings include a wide beamwidth 

(typically 6°), which limits the resolution and possibility of 

directly comparing the data to the 1° beamwidth available with 

weather radars. In our Phase I effort, we have determined 

solutions to several technical challenges with the design of a 

new instrument—the NASA Narrow beam, Multi-waveband 

NASA/CR—2010-216357 1 
 

Figure 1.—Image of the NNMSR located at the CSU 

CHILL radar site during the summer of 2009. 

Scanning Radiometer (NNMSR) that is to operate in concert 

with weather radars. This report will detail the design 

(Section 2.1), calibration (Section 2.2), overview of NNMSR 

channel data interpretation (Section 3.0) and field testing of 

the NNMSR at Colorado State University’s polarized CHILL 

S-band radar facility (Fig. 1, Section 4) for the application of 

improving in-flight icing hazard detection. This new sensor, 

when integrated into the existing NIRSS system and 

positioned near the soon-to-be-polarized NEXRAD radars 

near each large national terminal, can fulfill the need for 

airport terminal area icing hazard warnings. 

There are other possible applications of this new system 

beyond terminal area in-flight icing hazard detection that 

should be mentioned. The system could help nowcast the need 

for (or lack of need for) the application of deicing solutions in 

advance of departure, creating savings and reducing delays. 

The system could also provide valuable high resolution 

mesoscale meteorological inputs for weather and climate 

model initializations (Fabry and Meunier, 2009). The current 

research is only related to in-flight icing applications, 

however, and no other applications are being pursued as part 

of this work. 

2.0 System Realization 

2.1 Design 

The NNMSR project began when the Boulder, Colorado, 

based Radiometrics Corporation applied for and received a 

Small Business Innovation contract in 2004 to design and 

construct a turnkey, fast-sampling, multi-frequency, dual 

polarization narrowbeam radiometer system. The specified 

system was to include 21 channels in the K-band, and a 

separate W-band receiver. With its broad K-band sampling 

capability, it can integrate water vapor along the beam and 

provide information on the discrimination of liquid and ice 

phase hydrometeors utilizing the W-band polarization. By 

using data from both bands, liquid water path can be derived. 

The system also employs a fast beam steering system to 

operate in concert with a weather radar. Adding to these 

measurement capabilities the system’s full elevation and 

azimuth scanning capability results in a measurements with 

the potential of providing terminal area icing detection and 

warning. The importance of the technology described in this 

work is that the value of important radiometric observations 

provided by the NNMSR are greatly enhanced by matching 

the sample volume of research radars. 

The K-band (20 to 30 GHz) receiver was chosen for 

inclusion in the NNMSR because the band includes the peak 

and shoulder of a water vapor absorption line. By comparing 

the received brightness temperatures (TB) from a channel near 

the peak of the water absorption line to a second channel in 

the water vapor window region, values for integrated water 

vapor and integrated cloud liquid water can be obtained. This 

is because channels near the peak of the water vapor 

absorption line have an absorption coefficient for water vapor 

that is nearly independent of altitude. Channels well away 

from the water absorption peak are used because the received 

TB is dominated by the absorption and emission from liquid 

water (which increases with the frequency squared). 

The W-band 89 GHz channel, is sensitive to cloud liquid 

water but is also strongly affected by scattering from 

precipitation sized glaciated hydrometeors (Troitsky et al. 

2003). For this reason, the W-band receiver was separated into 

vertically and horizontally polarized receiver channels to 

attempt to discriminate cases when horizontally oriented 

glaciated particles were present. 

2.2 Calibration 

Figure 2 details relevant parameters and calibration 

procedures employed in the development of the operational 

NNMSR system. In the resulting passive radiometer system, 

all beams are collinear and match the antenna gain pattern of 

NEXRAD and weather research radars. Elevation and azimuth 

beam matching between the K and W band radiometers was 

achieved by scanning a 1° by 1° grid encompassing the tallest 

peaks on the Front Range near Boulder, Colorado. These 

peaks were located approximately 7 km in distance from the 

radiometer. Many hours of vertical and horizontal profiles 

across these mountain targets were averaged and analyzed so 

that precise vertical and horizontal beam matching was 

achieved. 

NASA/CR—2010-216357 2 
Figure 2.—Parameters of the NNMSR system. 

3.0 Data Interpretation 

Lohnert and Crewell (2003) used a large radiosonde profile 

dataset to model clouds in three different cloud models, which 

all used a modified adiabatic assumption and a threshold for 

relative humidity. They developed nine different regression 

algorithms of LWP for multi-frequency ground-based 

radiometers and applied them to data sets where clouds were 

generated by the threshold method, gradient method and a 

cloud microphysical model. The generalized form of the 

retrieval is 

LWP = c0 + c*TB (1) 

where c is the coefficient vector with dimensions defined by 

the number of frequencies of brightness temperatures as a 

vector, TB, used in the retrieval. For this study, a LWP 

algorithm was selected for use based on availability and 

proximity of NNMSR channels to those in the reference 

publication, shown as 

 LWP= c0 – 7.5*TB23.0 + 6.6*TB28.5 + 4.5*TB90.0 (2) 

which had an RMS of 19.8 gm–2 and a COR2

 of 0.96 between 

the modeled and retrieved LWP. In their study, they found that 

the inclusion of the W-band channel made a significant 

improvement in the LWP correlation statistics. For the case 

studies in the following section, we will compute the LWP in 

this fashion as part of the analysis. 

It is important to note that liquid water on the radiometer 

dish can result in artificially high values of brightness 

temperature. None of the cases explored in the following 

sections involved precipitation reaching the surface. 

4.0 Case Studies 

Two case studies are discussed in this section which 

elucidate how the new NNMSR system can be utilized in 

concert with polarized S-band radars to detect in-flight icing 

hazards in the airport operational environment. 

(a)

(b)

Figure 3.—Atmospheric profiles of ambient temperature (Ta) and 

dewpoint temperature (Td) from 12Z on September 21th (a) 

and from 00Z on September 22nd (b) from Denver, Colorado. 

4.1 September 21, 2009 

The first case study is from September 21, 2009, when a cold 

front moved southward from Canada over the CHILL site. The 

progression of the front can be seen in Figure 3(a), as wind barbs 

from the north below 700 mb, and in Figure 3(b) as a cooling of 

the ambient temperature Ta in the atmospheric profile up to 

400 mb and a deepening of the northerly wind layer. By the later 

time period, there is a slight drying of the lowest levels, but a 

moistening from 3.5 to 6.5 km AGL. The more dense cold air 

sliding southward behind the front is drying the lowest levels due 

to its continental origin. At the same time the lower-level airmass 

is providing just enough lift to the airmass above it that the upper 

airmass is becoming saturated and supercooled cloud droplets are 

forming. We know this to be true because this time corresponds 

NASA/CR—2010-216357 3 
to when four ‘moderate’ and one ‘light’ icing PIREP were 

reported within 1 hr and 10 nmi of the CSU CHILL instrument 

site. All of these PIREPs were reported in the layer between 4 and 

8 km in altitude. The freezing level lowers from 1.6 to 0.9 km by 

00Z on September 22nd. No precipitation reached the ground at 

any time during the times encompassing this case study. 

We’ll begin by looking at the CHILL moment data and 

NNMSR derived LWP and 89 GHz polarization differences 

around 18:00 Z on September 21. All of the radar data 

imagery presented in this work are from range-height indicator 

(RHIs) scan format from 1° to 30° beam elevations, which 

means the radar was viewing vertical slices of the atmosphere 

at a fixed azimuth. The signal in the radar velocity field 

(Fig. 4(a)) supports the synoptic view of a cold front affecting 

the radar site. Red and orange radial velocity values from the 

surface up to 3 km indicate flow away from the radar, and 

since the radar is pointed southward (175° azimuth) this lower 

layer is the cold, dense airflow from the north behind the cold 

front. Blueish values in the layer between 4 and 7 km altitude 

have a flow component from the south. Very low reflectivity 

values below zero dBZ (Fig. 4(b)) in the layer between 4 and 

7 km are consistent with findings in previous research (Serke 

et al., 2008) as an indicator to the presence of supercooled 

liquid in winter. The differential reflectivity (ZDR, Fig. 5(a)) 

is a ratio of the returned vertically and horizontally polarized 

signals and gives some information on the shape and 

orientation of the dominant particles being viewed by the 

radar. In the layer between 4 and 7 km where the icing 

PIREPS are being reported, ZDR values are slightly positive. 

Values from zero to slightly positive indicate the vertical and 

horizontal axial dimensions of the targets in the viewing 

volume are similar, which is consistent with rounded particles. 

The LWP field was derived for 18:04 Z (Fig. 6(a)) as shown in 

Equation (2). Since NNMSR in its current form is unable to 

range liquid, it helps to think of this image as a sector of sky 

centered on due south (180° azimuth) where each pixel is a 

range integrated measurement of LWP. The supercooled 

liquid, which is detected otherwise as numerous positive icing 

PIREPs, show up in this plot as horizontal streaks of elevated 

LWP in excess of 600 gm–2. The horizontal ‘streakiness’ is 

likely due to the passage of super-cooled liquid pockets across 

the viewed sky sector in the 14 minutes it took to collect all 

the NNMSR channel data for the sky sector. The visual view 

of the same sky sector (Fig. 7) comes from a webcam 

positioned on an instrument tower right next to the NNMSR 

and depicts a grey, stratiform cloud deck with occasional gaps. 

The 89 GHz channel was included as part of this system 

because not only is this band sensitive to emission from liquid 

water, but it is also affected by the reflection and scattering of 

microwave radiation from glaciated particles. Oblate ice 

particles such as dendrites tend to fall with their long axis 

horizontal. Radiation that is absorbed and emitted is naturally 

unpolarized (Fig. 8), thus the only way to receive a polarized 

signal is if the particle mass effectively polarizes the signal. 

This is theorized to occur in the presence of oblate crystals (or 

(a)

(b)

Figure 4.—CHILL RHI views from 175° azimuth of radial 

velocity (a), [ms–1]) and reflectivity (b), [dBZ]) at 18:00Z on 

September 21st. Vertical and horizontal ranges are in 

kilometers. 

Figure 5.—CHILL RHI views from 175° azimuth of differential 

reflectivity [dBZ] at 18:00Z on September 21st. 

NASA/CR—2010-216357 4 
(a)

(b)

Figure 6.—NNMSR derived LWP (a), [gm–2]), 89 GHz V-H 

(b), [°K] at 18:04 Z. 

large rain drops) as horizontal radiation is preferentially 

reflected from the surfaces of all the particles at the given 

viewing angle. When the horizontal component is larger than 

the vertical, V-H is negative. This is the case in Figure 6(b) for 

areas where LWP values are smallest. At elevations and 

azimuths where LWP is largest, 89 V-H is near zero which is 

consistent with viewing round liquid particles which emit 

unpolarized radiance. At elevation angles of 5° and below, 

channel values can be suspect due to surface effects (Troitsky 

et al., 2003). Quick calculations based on 800 gm–2 of LWP 

(from Fig. 6(a)) distributed through the upper cloud layer with 

a path length of 1500 m (from Fig. 4(b)) at a 20° slant angle 

leads to a significant liquid water content of 0.4 to 0.5 gm–3 

through the cloud depth. This significant level of liquid water 

content is producing the local reports of moderate in-flight 

icing. 

Four hours later at 22:00Z, there were no reported icing 

PIREPs within 1 hr and 100 nmi of the CHILL instrument site. 

Both the radar and radiometer were operating in the same 

respective modes of viewing RHIs along 175° azimuth for 

CHILL and a similar southern-facing sky sector for the 

Figure 7.—Visual sky sector image at 18:04 Z. 

Figure 8.—Schematic of unpolarized microwave radiation 

becoming polarized and how horizontally oriented crystals 

create TBV – TBH < 0. 

NNMSR. The change in radar and radiometer signals from 

the earlier icing time period is dramatic. The radial velocity 

(Fig. 9(a)) field shows consistent flow from the north from the 

cloud base at 1 km AGL up to 5 km altitude. This is again 

consistent with a deepening layer of cold air flowing 

southward after a cold frontal passage. The reflectivity RHI 

(Fig. 9(b)) shows nearly all values are now above 0 dBZ, with 

the bulk being above 10 dBZ. Streamers of virga are seen 

reaching downward below the clouds, indicating that particles 

are large and weighty enough to begin falling out of the cloud, 

but are sublimating before they reach the surface. ZDR values 

(Fig. 10(a)) are somewhat positive near the cloud base and 

average about +1 dB near the cloud tops, consistent with small 

particles that are somewhat oriented. All of these clues from 

the CHILL moment data lead to the conclusions that the 

particle population in this increasingly cold cloud layer has a 

uniformly high reflectivity and a uniformly consistent shape 

and/or particle orientation. This particle mass must be almost 

fully glaciated, which is partially supported by the lack of 

positive icing PIREPs at a time of day when a significant 

volume of air traffic was transecting the region. 

NASA/CR—2010-216357 5 
(a)

(b)

Figure 9.—CHILL RHI views from 175° azimuth of radial 

velocity (a), [ms–1]) and reflectivity (b), [dBZ]) at 22:04Z on 

September 21st. 

Figure 10.—CHILL RHI views from 175° azimuth of differential 

reflectivity [dBZ] at 22:04Z on September 21st. 

Figure 11.—Gridded visual sky sector image at 22:28 Z 

on September 21st. 

(a)

(b)

Figure 12.—NNMSR derived LWP (a), [gm–2]), 89 GHz V-H 

(b), [°K] at 22:28Z on September 21st. 

The south-facing visual sky sector image (Fig. 11) shows a 

grey stratiform cloud deck with no gaps, with what appears to 

be blue skies at low elevation angles. Retrieved LWP 

(Fig. 12(a)) values at angles above 10° are uniformly below 

300 gm–2, which is half to one-third the values seen at the 

NASA/CR—2010-216357 6 
earlier case time. Figure 12(b) shows negative 2° to 3° V-H 

differences at viewing angles above 10°. This is due to 

relatively large (warm TB) emission from water droplets in the 

lower levels of the atmosphere being more preferentially 

scattered by horizontally oriented ice particles in the horizontal 

component than the vertical component back towards the 

passive NNMSR, thus creating a negative V-H channel 

difference. One curious feature of the LWP and 89 V-H views 

are the large values of each field below 10° elevation. Troitsky 

et al., (2003) demonstrated that theoretically calculated 

polarization differences at 85 GHz became large and positive at 

low viewing angles in the presence of horizontally oriented 

oblate particles (such as plates, dendrites or rods). Since the 3 

GHz CHILL radar ZDR is just slightly positive and the much 

higher frequency 89 GHz V-H is significantly negative, the 

preferentially oriented particles must be fairly small and not 

made up of larger dendrites.

4.2 September 12, 2009 

Late on September 12th, an easterly wind component behind a 

cold front led to the formation of discretely layered upslope 

clouds. Two light icing PIREPs were recorded within 1 hr and 

100 nmi of the instrument location at CHILL. By 12:00Z, the 

Denver temperature sounding (Fig. 13) had a freezing level at 

about 2 km altitude and a nearly saturated profile above 1.5 km 

that became saturated by 00Z on September 13th. The RHI 

reflectivity field (Fig. 14) looking south at 185° azimuth from 

CHILL exhibits three distinct cloud layers—centered on 3.7, 2 

and 0.5 km altitude. The vertical height scale of the reflectivity 

scale is matched up with the vertical scale of the temperature 

sounding for ease of comparison. All three layers offer only weak 

returns, with most values being below zero and only pockets of 

the upper layer reaching 6 dBZ. Analysis of the ZDR field (Fig. 

15(a)) leads to very interesting ramifications for the ability of 

satellite based detection methods to detect icing in this case. One 

can see that the lowest two layers have slightly positive ZDRs, 

indicating nearly round or axial-symmetric shapes of the 

reflectivity-weighted particle distribution. The upper level, 

however, has a mean ZDR of about +2 dB. This means that the 

dominant reflectivity-weighted hydrometeors in the volume are 

horizontally oriented. Significantly oriented particles at –15 °C 

must be plates or dendrites as opposed to oblate large raindrops, 

and since the layer reflectivity is so low the glaciated particles 

must be small and sparse. 

On this day, the radiometer was collecting data every 5° 

azimuth and elevation with 1° resolution, which is why the image 

resolution (Fig. 16(a)) seems reduced compared to the previous 

case study. The LWP field has discrete regions of relative 

maxima of about 350 gm-2 at elevations above 10°. Relative 

maxima in LWP spatially correspond to 89 V-H values near zero 

(Fig. 16(b)), which is consistent with round particles. Other areas 

above 10° elevation have V-H values of –1 dB or below, which is 

consistent with oriented particles. The visual view of the sampled 

sky sector in Figure 17 shows a continuous grey stratiform cloud 

deck. 

Figure 14.—CHILL RHI view from 185° azimuth of reflectivity 

(b, [dBZ]) at 16:37Z on September 12th. 

Figure 15.—CHILL RHI views from 185° azimuth of differential 

reflectivity [dBZ] at 16:37Z on September 12th. 

NASA/CR—2010-216357 7 
(a)

(b)

Figure 16.—NNMSR derived LWP (a), [gm-2]), 89 GHz V-H 

(b), [°K] at 16:37Z on September 12th. 

Figure 17.—Gridded visual sky sector image at 16:37 Z on 

September 12th. 

The important fact to note in this case is that satellite-based 

visible and infrared icing detection methods will sense only 

the glaciated upper layer of clouds and not be able warn for inflight icing for the cloud layers lower down. Also, icing in 

multi-layer clouds are a very important scenario to detect since 

they can lead to sequenced icing events that can be more 

dangerous and unpredictable for controlled flight than icing 

from deeper single layered clouds. A ground-based system 

such as the NASA Icing Remote Sensing System, of which 

NNMSR will be a part, can efficiently detect the icing threat 

in the middle layer when positioned with a polarized S-band 

radar. 

5.0 Summary 

The first purpose of this summer field program was to test 

the new, one-of-a-kind system for robustness and stability. 

After the two months of field testing and data collection, the 

scanhead drive and receivers seemed very stable. The system 

was operated remotely in an automated fashion for most of the 

test period. 

The second purpose of this study was to determine if the 

new NNMSR could aid in the detection of in-flight icing 

hazards. One case study time had multiple icing PIREPs 

located close to the instrumentation. Low radar reflectivity 

(<0 dBZ) indicated a lack of large reflectors. High radiometer 

LWP values and no preferred particle orientation were 

consistent with the presence of significant liquid drops aloft at 

a time with many positive icing PIREPs. At a later time with 

no reported PIREPs, high radar reflectivity (>10 dBZ) 

indicated the presence of large reflectors which are known to 

effectively scavenge available liquid drops. Positive ZDR 

values meant somewhat oriented particles. Low radiometer 

LWP values and a horizontal particle preference detected in 

the 89 GHz V-H signal were consistent with an all glaciated 

cloud and no icing PIREPs. 

The second case study had three discrete cloud layers, the 

top of which was clearly glaciated based on the radar ZDR 

values. Two ‘light’ icing PIREPs were reported roughly at the 

height of the middle cloud layer. Satellite-based in-flight icing 

hazard warning systems, such as CIP, would not be able detect 

icing conditions in this case since they can only detect the 

highest cloud top. The NNMSR products were able to discern 

patchy relative maxima in LWP and 89 GHz V-H differences 

consistent with more round particles. 

Based on the system’s overall stability and ability to detect 

elevated LWP in association with icing verification from 

PIREPs, we have determined that the NNMSR would be a 

valuable addition to NIRSS for detecting in-flight icing 

hazards in the airport environment. This will especially be true 

in the coming years as the national network of S-band 

NEXRADs are upgraded to collect polarimetric moment data, 

as was available for this study at CSU’s CHILL. 

NASA/CR—2010-216357 8 
NASA/CR—2010-216357 9 

Future work includes more summer 2009 case analysis by 

averaging the CHILL moment data along the radar beam and 

comparing the results to radiometer LWP. Also, it might be 

useful to compare areal averaged GOES LWP product to 

radiometer LWP for the collected case studies. In 2010, the 

NNMSR will be positioned at NASA Glenn Research Center 

with NASA’s Icing Remote Sensing System. Work will focus 

on applying the NIRSS algorithms with the NNMSR and 

NEXRAD data. 

References 

Bernstein, B., McDonough, F., Politovich, M., Brown, B., Ratvasky, 

T., Miller, D., Wolff, C., and Cunning, G., “Current Icing Potential: 

Algorithm description and comparison to aircraft observations,” 

Journal of Applied Meteorology, 44, pp. 969–986, 2005. 

Fabry, F., and Meunier, V., “Conceptualisation and design of a 

Mesoscale Radiometer,” 8th International Symposium on 

Tropospheric Profiling, S06–P03–1, Delft, NL, 2009. 

Lohnert, U., and S. Crewell, “Accuracy of cloud liquid water path 

from ground-based microwave radiometry, 1, Dependency on 

cloud model statistics,” Radio. Sci., 38(3), 8041, 2003 

Reehorst, A., Politovich, M., Zednik, S., Isaac, G., and Cober, S.,

“Progress in the Development of Practical Remote Detection of 

Icing Conditions”, Report NASA/TM—2006-214242, 2006. 

Serke, D.J., F. McDonough and M. Politovich, “Analysis of 3-D 

NEXRAD Mosaic Reflectivity Data Collocated with Research 

Aircraft and Satellite Data: Implications on In-Flight Icing,” 13th

Conference on Aviation, Range and Aerospace Meteorology 

Preprint, New Orleans, LA, Jan. 20–25, 2008. 

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“Thermal Microwave Atmospheric Radiation Due to Scattering 

by Ice Particles in Clouds,” Journal of the Atmospheric Sciences, 

60, pp. 1608–1620, 2003. 
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1. REPORT DATE (DD-MM-YYYY)

01-07-2010 

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Final Contractor Report 

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4. TITLE AND SUBTITLE

A New Narrowbeam, Multi-Frequency Scanning Radiometer and Its Application to In-Flight 

Icing Detection 

5a. CONTRACT NUMBER

NNC06E046T 

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Serke, David, J.; Beaty, Paul; Kennedy, Pat; Solheim, Frederick; Ware, Randolph; Politovich, 

Marcia, K.; Brunkow, David; Bowie, Robert 

5d. PROJECT NUMBER

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WBS 609866.02.07.03.04 

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National Center for Atmospheric Research 

P.O. Box 3000 

Boulder, Colorado 80307-3000 

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E-17293 

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National Aeronautics and Space Administration 

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NASA 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

A narrow-beam (1° beamwidth), multi-channel (20 to 30 and 89 GHz), polarized (89 vertical and horizontal) radiometer with full azimuth 

and elevation scanning capabilities has been built with the purpose of improving the detection of in-flight icing hazards to aircraft in the near 

airport environment. This goal was achieved by co-locating the radiometer with Colorado State University's CHILL polarized Doppler radar 

and taking advantage of similar beamwidth and volume scan regiments. In this way, the liquid water path and water vapor measurements 

derived from the radiometer were merged with CHILL's moment fields to provide diagnoses of water phase and microphysics aloft. The 

radiometer was field tested at Colorado State University's CHILL radar site near Greeley, Colorado, during the summer of 2009. Instrument 

design, calibration and initial field testing results are discussed in this paper.

15. SUBJECT TERMS

Aircraft icing; Radiometers; Meteorology; Meteorological radar; Clouds (meteorology); Aircraft hazards; Aviation meteorology; 

Aircraft safety 

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