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