working group on space-based lidar winds destin, florida february 3, 2010 tom apedaile
DESCRIPTION
ValidWind ™: Improved Techniques and Results for Ground-Based Remote Sensing of Low Altitude Wind Profiles. Working Group on Space-Based Lidar Winds Destin, Florida February 3, 2010 Tom Apedaile Bill Bradford Alan Marchant Danny Scholes Tom Wilkerson. ™ USU Research Foundation, 2009. - PowerPoint PPT PresentationTRANSCRIPT
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Working Group on Space-Based Lidar Winds
Destin, Florida
February 3, 2010
Tom Apedaile
Bill Bradford
Alan Marchant
Danny Scholes
Tom Wilkerson
™ USU Research Foundation, 2009
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ValidWind capabilities:• horizontal range 2km
• altitude range 1km
• velocity accuracy 1% at all wind speeds
• direction accuracy 1º for v > 1m/s
• profile resolution 20m
• profiling rate 5 – 10 min
• small balloon tracer- 11” He-filled latex
• retroreflector tape
• laser rangefinder- built-in inclinometer
- integrated compass
- bluetooth data link
• 3D balloon trajectory
• trajectory analysis S/W
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The ValidWind Concept
• Applications for Local Wind Profiling
• Intrinsic Accuracy and Aerodynamics
• Data Processing
• Validation Campaigns
• System Improvements
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Aug 19
Aug 20
• proposed wind turbine site at the mouth of Logan canyon
• supplementary power for USU campus
• exploit canyon drainage wind• campaign results:
- nocturnal jet develops from the bottom up, then decays coherently
- ideal turbine height ~ 100m (unobtrusive)
- jet duration 11 hours (winter evaluation needed)
time of day (MDT)
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-200 0 200 400 600 800 1000 1200 1400-200
-100
0
100
200
300
400
horizontal distance (m)
alti
tud
e w
.r.t
. se
nso
r (m
)
v > 7 m/s
v < 7 m/s
leeward terrain
• wind field cross-section projected to plane 52 from North (the prevailing wind direction on 9/19/09)
• strong updraft at the ridgeline transitions to a strong leeward downdraft• horizontal velocity steady at 7.8 ± 1.3 m/s• vertical flow shifts dramatically from +1.6 to -3.5 m/s• preferred turbine location may be slightly leeward
wind vector field constructed from multiple balloon trajectorieswind vector field constructed from multiple balloon trajectories
Clarkston ridge, West of Logan9/19/09
NE
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Danish Flats campaign.
ValidWind profiling was performed over or near the processing facility.ValidWind profiling was performed over or near the processing facility.
Air-quality campaign at Danish Flats treatment facility, 10/22-26/09
• ValidWind used to monitor wind profiles.
• Wind data coordinated with other instruments to assess fluxes.
• Wind data Balloon flights coordinated to provide profiles over the facility.
• Good agreement with a 15m tower.
• Comparison w/ Remtech sodar.- average speed and direction ok
- sodar yields poor profile accuracy
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Jimsphere• Metalized balloon, tracked
by radar.• Intentionally roughened to
minimize “lift instabilities.”• “Standard for upper level
wind measurement.”
PIBAL – Pilot Balloon• First described ~1872.
• Developed to check upper level winds before manned balloon flights.
• Passive balloon.
• Direction measured by theodolite.
• Range based on a typical rate of ascent.
Rawinsonde• Weather balloon with
telemetry.
• Trajectory traced by GPS.
• Flights may last hours and extend above the troposphere.
All of these balloons have limited advection accuracy.All of these balloons have limited advection accuracy.
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Balloon motion relative to the wind.
CD, Re, terminal velocity
Lift-induced perturbations.
Transient slip.
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air
air DU
Re
Aerodynamic properties scale with Reynolds number:
where U = velocity (rate of rise) and D = diameter.
For ValidWind, D 13”, Vz ~ 2 m/s, Re ~ 44,000.
For weather balloons, D 2m, Vz ~ 7 m/s, Re ~ 900,000.
The drag coefficient is a function of Re defined by:22
8DUCF airDdrag
subcritical flow
supercritical flow
transition from laminar to turbulent boundary layer
CD = 0.4 – 0.5 for all Re of interestCD = 0.4 – 0.5 for all Re of interest
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Terminal rate of rise is reached when the drag force cancels the loft:
or
For the nominal ValidWind parameters, Vz = 2.0 m/s.
Observation:
• Loss of He reduces the loft and the expected Vz. (Latex is leaky.)
• Up/down drafts contribute variability.
• The results are consistent with the spherical balloon model.
2/1
2
8V
DCD
z
DF
trajectory-averaged rate of risetrajectory-averaged rate of rise
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“Lift” is an aerodynamic force normal to motion through the fluid.
The lift coefficient is analogous to the drag coefficient:
Experiments and simulation show CL fluctuating with an amplitude 0.05 – 0.1 for subcritical flow. Fluctuations in CD are much smaller.
The typical fluctuation frequency is with a Strouhal number S ~ 0.1 – 0.2. For ValidWind, the fluctuation frequency is 0.5 – 1 Hz.
Trajectory perturbations are estimated by integrating the equation of motion:
where m’ is the balloon inertial mass plus the aerodynamic “added mass.”
For ValidWind, with worst-case values of CL and S, the rms velocity perturbation is V < 0.2 m/s. This is strongly damped by trajectory averaging.
22
8DUCF airL
DUSfL /
)2sin(2
x2
tfm
AVC L
zL
For super-critical flow, CL is somewhat larger. More importantly, CL develops significant power at low frequencies.
mS
DVCV zL
16
3
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How does the balloon respond to a large velocity offset?• V with respect to the vertical terminal velocity
• balloon launched, starting from rest
• balloon passes through an abrupt sheer layer
Equation of motion:• ignoring perturbations due to lift and turbulence
• co-moving coordinate system
Solution for transverse motion:
where atan(V/Vz) and
Transient decay is approximately exponential with a time constant of order 1s.
For V = 2 m/s, total slip is < 1m.
zu8
a2
mm
DuCD
te )2/tan()2/tan( 0
m
DVC zD
8
2
It’s very hard to throw a balloon.It’s very hard to throw a balloon.
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Raw Data collected by MatLab scriptRaw Data collected by MatLab script
compass inclinometer rangefinder timetagflight resetpre-flight trial
dust
Parse Data remove false readingsParse Data remove false readings
. . . e.g. rangefinder failures, background or foreground interference, telemetry errors.
Convert Data to Cartesian coordinatesConvert Data to Cartesian coordinates
East North AGL t
Filter Data w.r.t. time & Fit Velocity Vector
Filter Data w.r.t. time & Fit Velocity Vector
• accommodate asynchronous trajectory sampling• low-pass temporal filter with a uniform scale• smooth the trajectory and estimate velocity in a
single step (minimize processing noise)• accommodate wind shear
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• Gaussian-weighted Quadratic Least squares Filter.
• A type of LOESS (locally estimated scatterplot smoothing) filter.
• MatLab m-file: gqlf(t, ti, X, sigma)
{X} are measurements of a cartesian coordinate corresponding to {t}.
{ti} are the evaluation times, bounded by {t}.
The weighting function is exp(-t2/2sigma2). = 10s, typical
Returns NaN if data density is too low (less than 3 data points within ti±3).
• Return values:
qF.b0 profile estimate (at each value ti) balloon trajectory
qF.b1 slope estimate (dX/dt) velocity profile
qF.b2 2nd derivative estimate (d2X/dt2) ~ wind shear vz
qF.err weighted fit error (indicates pointwise quality of b0)
• Inputs need not be uniformly spaced.
• Filter resolution is uniform all along the trajectory.
• For ValidWind vector profiles, repeat GQLF for x, y, and z.
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-1400 -1200 -1000 -800 -600 -400 -200 0-1000
-500
00
200
400
600
800
1000
1200
1400
1600
Danish Flats
10/26/09, 10:39 am MDT
GQLF filter with = 10s
Danish Flats
10/26/09, 10:39 am MDT
GQLF filter with = 10s
altit
ude
(m,
AG
L)
NorthEast
insufficient sample rate
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0 100 200 300 400 500 600 700 800 900 10000
1
2
3
4
5
6
time (seconds)
rms
tra
ject
ory
sm
oo
thin
g r
esi
du
al (
m)
x component (EW)
y component (NS)
z component (vertical)
• residual errors typically 1 - 2m, consistent with sensor precision and pointing repeatability
• errors due to pointing increase with range (r x d)• velocity uncertainty from a 2m residual is < 0.1m/s
Flig
ht #
1, 1
0/26
/09,
Dan
ish
Fla
ts
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Boulder Atmospheric Observatory
300m met tower
Sept 30, 2009
(Dan Wolfe, NOAA)
miniMOPA Doppler Lidar
Sept 29, 2009
(Alan Brewer et al., NOAA)
BAO tower40.0500-105.0039latitude 40.05
longitude -105.01per MapQuest
ValidWindinstrument40.0448-105.0056
ValidWind campaign, September 29, 2009.The location was selected to provide balloon tracks passing the miniMOPA outside its 1 km “dead zone.” Initial wind was from the South.
mMOPA lidarlatitude 39.9701longitude -105.1178
ValidWindinstrument39.9634-105.0996
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• wind velocities are consistent
• wind direction offset calibrate ValidWind compass
• wind velocities are consistent
• wind direction offset calibrate ValidWind compass
10 11 12 13 14 15 16 17 180
2
4
6
8
10
12
14
16
18
20
win
d sp
eed
(m/s
)
time (hours, MDT)
ValidWind vs. BAO: -0.25 ± 1.4
win
d so
urce
dire
ctio
n (d
eg)
10 11 12 13 14 15 16 17 180
45
90
135
180
225
270
315
360
ValidWind vs. BAO: 28º ± 1.0
Val
idW
ind
resu
lts a
t 10
0m v
s.
BA
O a
nem
omet
er a
t 10
0m
sim
ilar
resu
lst
at 5
0, 1
50,
& 2
00m
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12 13 14 15 16 17 18 19 20 210
100
200
300
400
500
600
700
800
900
time (MDT)
alti
tud
e (
m, A
GL
)
ValidWind, Boulder, CO, 9/29/09
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5wind speed (m/s)
00:00 UTC
excellent qualitative agreement• wind directions• wind shift event at 23:00 UTC• wind profile features
arrows show wind direction; colors show wind speed
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quantitative agreement in the early afternoon and evening
• wind velocities• profile features• lidar shows a homogeneous, area-
wide wind field
-6 -4 -2 0 2 4 60
100
200
300
400
500
600
700
800
900
100019:37 MDT, 9/29/09
wind velocity component (m/s)
alti
tud
e (
m, A
GL
)
ValidWind NS
ValidWind EWmMOPA NS
mMOPA EW
-6 -4 -2 0 2 4 60
100
200
300
400
500
600
700
800
900
100016:39 MDT, 9/29/09
wind velocity component (m/s)
alti
tud
e (
m, A
GL
)
ValidWind NS
ValidWind EWmMOPA NS
mMOPA EW
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Agreement fails when:• wind shift event at 23:00 UTC• lidar shows strong wind field inhomogeneity
mMOPA verifies a local Easterly wind component
-6 -4 -2 0 2 4 60
100
200
300
400
500
600
700
800
900
100017:23 MDT, 9/29/09
wind velocity component (m/s)
alti
tud
e (
m, A
GL
)
ValidWind NS
ValidWind EWmMOPA NS
mMOPA EW
map of Doppler residuals over the ValidWind site
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Automatic balloon tracking• increased tracking accuracy
• increased sample frequency
• eliminate human limitations on balloon tracking
compass
rangefinder
motorized gimbal
tracking camera
Real-time data processing.• manage the video tracker
• automatic data parsing
• field displays of trajectories and wind profiles