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
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
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
The ValidWind Concept
• Applications for Local Wind Profiling
• Intrinsic Accuracy and Aerodynamics
• Data Processing
• Validation Campaigns
• System Improvements
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)
-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
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
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.
Balloon motion relative to the wind.
CD, Re, terminal velocity
Lift-induced perturbations.
Transient slip.
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
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
“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
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.
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
• 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.
-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
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
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
• 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
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
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
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
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