Kirtzel, Hans-Jürgen: FM-CW Wind Lidar “Wind Ranger” and Multi-Path Sonic “uSonic-3 MP”

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Wind Ranger 100/200
FM-CW Doppler Wind Lidar for Wind Profiles for Low Range Wind Profiles
Hans-Jürgen Kirtzel, Metek GmbH
1
ICOS Meeting 2022, Utrecht

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LiDAR Basics - How to Calculate Wind Vectors
2
Scattering at aerosol particles
Laser source
 Transmitted laser signal is back scattered at aerosol particles
 Scattered signal is Doppler shifted as aerosol moves with the
wind.

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θ
Tildt angle θ
x = horizontal wind
component
laser beam, line of sight (LOS)
Emitted frequency fE
Received frequency fR
Doppler shift f = (fR – fE)
Light velocity c
Radial wind component VR ≈ c · f /(2·fE)
Horizontal wind component x = VR / sin θ
Reflected signal is Doppler shifted
-> LiDAR measures radial wind component
laser beam
moving
areosol
VR = wind component projected on the LOS

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LiDAR Basics – How to Calculate Windvectors
4
To calculate three orthogonal components of the unknown wind vector
(x, y, z)

... requires three independent radial components
(VR1, VR2, VR3)

... And so it requires measurements on at least three non-complanar beams.

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Δϕ ≥ 30
VAD,
3 beams (typ. 6 - 8 beams) or continuous scans
Doppler Beam Swinging
(DBS), 3 beams
(1 vertical recommended)

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radial
windspeed
azimuth
Top view of typical scan pattern: VAD scan mode
windspeed
vertical windspeed
wind direction

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A new family of FM-CW Doppler LiDARs
7
Continuous Wave Ranging by focus adjustment
Short range, 7 … 100/200 m
High spatial and temporal resolution, 0.08 … 16/32 m, ≥ 1 s
Range gates measured sequentially
Pulsed Ranging by travel time, dead band approx. 50 m … 100 m (100 ns … 400 ns)
Long range, max 12.000 m @ 10 kHz
Low spatial and temporal resolution, ≥ approx. 20m, ≥ 10 s
All ranges simultaneously

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A new family of FM-CW Doppler LiDARs (effects of narrow cone angle)
8
0 10 20 30 40 50 60 70 80 90 100
0
20
40
60
80
100
120
140
160
180
200
Radius of Measurement Cone
Height
10° zenith
30° zenith
Effects on small cone angle (10 ° vs. 30 °)
• Measurements at narrow sites available (urban areas, street canyons,
forest clearings, …)
• Smaller separation between measuring volumes, i.e. assumed flow
homogeneity more easily fulfilled
• High measuring sensitivity to vertical wind component
h1
h2
h3
h4
h5
10 ° zenith angle
30 ° zenith angle

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h1
h2
h3
h4
h5
Due to geometric reasons the separation of focal areas from neigbored ranges
becomes worse with increasing ranges!

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h1
h2
h3
h4
h5 Due to geometric reasons the separation of the focal area from neigbored ranges
becomes worse with increasing ranges!
In case of strong changes of the back scattering along the propagating path the
localization by the focal effect can be impaired,
e.g. the optics is adjusted to 100 m but the main signal contribution originates
from 300 m (from a low hanging cloud) and the wind speed is falsely measured.
The frequency modulation used at first time in Wind Lidar technique allows
to determine the range of the „effective“ measuring volume!
Height / Lens diameter 2“ lens 3“ lens
10 m 0,16 m 0,08 m
20 m 0,64 m 0,32
100 m 16 m 8 m
200 m 64 m /NA 32 m

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11
FW-CW Wind Lidar Wind Ranger 100/200
• Tri-angular frequency modulation
• Ranging by focus adjustment, no dead band
• Short range, 7 … 100/200 m
• High spatial and temporal resolution, 0.08 … 16/32 m, ≥ 1 s
• Range gates measured sequentially
• Low hanging clouds overcompensate the spatial separation between neigbored measuring heights, but the
effective measuring height is known (quality check)
• No blind zone at zero wind component
• Sign of radial wind is determined, no further wind device needed

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Time
Optical
Frequency
VR = 0
Time
0
𝑓+ 𝑓−
12
„negative frequencies are measured
at the receiver as positive values“
Observed
frequency
Triangular modulation
The transition intervals 𝜏
(dashed beat frequency) are
discarded.
𝜏 is short compared with the
observation time.
𝜏 = 2𝑟 𝑐 , with 𝑟 = ℎ cos 𝜃
range of the focal spot.

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Time
Optical
Frequency 0
Time
𝑓+ 𝑓−
Doppler shift
13
VR > 0
Observed
frequency

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Time
Optical
Frequency
Time
0
𝑓+ 𝑓−
14
Doppler shift
VR < 0
Observed
frequency

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uSonic-3 Scientific, 15 m
(appearent tilt angle of mast
only due to a sub-optimum
camera operation)
Measuring volume of
Wind Ranger is about
0.4 x 0.4 x 0.4 m @ 15 m
height
15
Metek Wind Ranger
Comparison Wind Ranger (15 m) to Sonic Anemometer (15 m), at Airfield „Hungriger Wolf“, July 2018

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Metek Wind Ranger 100
10 minute averages
10 minute averages

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10 minute averages

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(A constant factor was applied to Lidar data to compensate the volume averaging effect.)
10 minute averages

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(A constant factor was applied to Lidar data to compensate the volume averaging effect.)
10 minute averages

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Free air signal, 10 m distance Signal from hard target, 20 m distance
Measurements in Precence of Strong Echoes, Spectrum
Internal reflection,
2 m distance
20
Separation of real atmospheric signal and
unwanted signals from other heights;
possible due to frequency modulation

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Flow Measurements in Precence of Strong Echoes, Spectrogram
Internal reflection,
≈ 2 m distance
Wind signal,
10 m distance Reflection from hard target,
20 m distance
21
Separation of real atmospheric signal
from adjusted 10 m distance and
unwanted signals from other ranges;
possible due to frequency modulation
Measurements

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„Perfect Day“, 24.08.2022
Setting of heights is user defined, e.g. 7 + 10 + 13 16+ 20 + 50 would be possible
22

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Mast Comparisons
23

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General Specifications Wind Ranger 100/200
Transmitted wavelength 1550 nm, eye safe according to Class 1M
Aperture 50 mm / 75 mm
Power consumption 60 W without cooling / 200 W with cooling
Power input 15 … 36 V
Size Enclosure dimensions (H x W x D) 620 mm x 530 mm x 340 mm
(incl. 4 height adjustable supports) 840 mm x 540 mm x 580 mm
Weight 50 kg approx.
Temperature range -30 … 45 °C
Windspeed range 0 … 100 m/s
Data rate 100 Hz (radial)
1 Hz (wind vector)
Communication LAN
Data format NetCDF, ASCII
24
Metek Wind Ranger

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Multi-Path Ultrasonic Anemometer
uSonic-3 Class A MP and Cage MP
MOSAIC 2020/2021
North Polar Drift Campaign
Photos on courtesy of
Matthew Shupe, NOAA
uSonic-3 Cage MP

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Demands:
• Must be accurate, minimizing shadow effects and flow distortion
• Must sustain and perform in nearly all weather types
• Must be serviceable for the next 2 decades
• Must cope with all common data aquisition techniques
• Must allow flexibility in the setup
• Must provide sophisticated onsite monitoring of system status and data quality
• Must allow internal data storage
Priorities
• Priority on vertical wind measurement
• Priority on strong vertical inflow angles
26
Motivation:
How to built the most advanced ultrasonic anemometer for turbulence
measurements?

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Demands:
• Must be accurate, minimizing shadow effects and flow distortion
• Must sustain and perform in all weather types
• Must be serviceable for the next 2 decades
• Must cope with all common data aquisition techniques
• Must allow flexibility in the setup
• Must provide sophisticated onsite online system status monitoring
• Must allow internal data storage
Priorities
• Priority on vertical wind measurement
• Priority on strong vertical inflow angles
Motivation:
measurements?

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MP Concept
here: measurements of vertical component with minimum of flow distortion
Transducers are aligned vertically to each other

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MP Concept of Vertically Aligned Transducers and Multiple Measuring Paths
• 3 x 3 measuring paths
• 6 tilted measuring paths
• 3 vertically aligned paths
• 6 tilted radial winds
• 3 vertical winds
• 6+3 virtual temperatures
• Automatic derivation of x, y, z and
Tv from advantageously positioned
paths
• Flow distortion minimized!
• Shadow effects minimized!
• Redundancy allows even operation
in case of a transducer failure
(waiving the MP benefits)

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Selection of the wind ward positioned measuring path, works also for strong vertical wind components

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0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
1.40
1.50
0 30 60 90 120 150 180 210 240 270 300 330 360
Gewichtung
()
Anströmrichtung (°)
Weighting Function Vertical Paths
g1a g1b g2a g2b g3a g3b
The weighting functions for the vertical wind component are identical for the Class A MP and Cage MP

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MP Concept
here: measurements of vertical component with minimum shadow effect.
T2
sonic path with length
T1 sonic transducer with diameter
r i wind component 2
Slope
(d(r/vel)/d𝜃
90° 60° 0°
120°
180°
= 22
𝑟
90° 60° 0°
120°
180°
responce function of shadow effect (left) and its first derivate (right)
green arrow indicates a vertically aligned measuring path
𝑟
= − − − 2
with = cos 𝜃 and = 𝑓(

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Demands:
• Must be accurate, minimizing shadow effects and flow distortion Vertical paths, Multi-Path technique
• Must sustain and perform in practically all weather types Icing protection by smart heating,
-40 … 60 °C temp. range, online quality check
• Must cope with all common data aquisition techniques Output via RS422, Ethernet, SD card, 4 analog ports
• Must allow flexibility in the setup Independent setting of output ports
• Must provide sophisticated onsite system status monitoring Analysis of analog sonic signals for status check
• Must provide online system status monitoring Status signals are part of output protocol
• Must provide data safety Internal data storage of 8 / 64 GB SD card
• Must be serviceable for the next 2 decades Components used in car industry
Priorities
• Priority on vertical wind measurement Vertical paths
• Priority on strong vertical inflow angles Vertical paths
Motivation:
measurements

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Conclusion 1
Wind Ranger 100/200 is a compact, light weight and easy-to-deploy FM-CW Lidar for
measurements of the 3D wind vector for profiling up to 200 m starting at 7 m agl and fine
height (starting at 8 cm/s) and time resolution (1 s).
Conclusion 2
Multi-Path sonics Class A MP and Cage MP uses 3 x 2 tilted and 3 vertical measuring paths
to derive wind and tiurbulence data with minimized shadow effect and minimized flow
distortion. The offer various output techniques, flexible operation, internal data storage,
smart heating functions and online monitoring of sensor status and data quality.
Thank you for your attention!

Kirtzel, Hans-Jürgen: FM-CW Wind Lidar “Wind Ranger” and Multi-Path Sonic “uSonic-3 MP”

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