B. Gentry/GSFCSLWG 06/29/05 Scaling Ground-Based Molecular Direct Detection Doppler Lidar...

B. Gentry/GSFC SLWG 06/29/05

Scaling Ground-Based Molecular Direct Detection Doppler Lidar

Measurements to Space Using Wind Profile Measurements from

GLOW

B. Gentry, J. Comer, M. McGillNASA / GSFC


Q: How can we use ground based measurements to refine and validate future space based lidar system designs?

1) Validate the instrument performance behaves predictably versus measurable quantity (signal photocounts; signal to noise) under a variety of conditions.

2) Establish reference system designs to examine impact of performance trades (e.g. spatial and temporal averaging schemes) or engineering trades

3) Scaling of ground based system performance to equivalent space-based system reveals where improvements are required and provides direction for technology and instrument system development programs

4) Scaling also provides a sanity check for space based designs


Mobile Lidar Optical Layout


-0.5

0

0.5

1

1.5

2

2.5

3

-6 -4 -2 0 2 4 6

Lidar Signal vs. Etalon Transmision

Frequency (GHz)

Edge2 Filter

Locking Filter

Edge1 Filter

Aerosol Spectrum

Rayleigh Spectrum

Double Edge Etalon Channels


Wind Measurement and Error Analysis

• Case study: Field measurements of wind speedand direction in stable atmospheric conditions

• HARGLO-2, November 16, 2001 • Algorithms used to determine wind speed and direction• Error analysis based on shot noise limited error


101 102 103 104 105 106

Edge 1 Detected Photocounts

0

5

10

15

20

25

30

Altitude (km)

11/15/01 23:48 (80 mJ)11/16/01 12:58 (65 mJ)11/16/01 16:14 ( 2 mJ)11/16/01 22:30 (30 mJ)11/17/01 16:48 ( 2 mJ)11/19/01 22:23 ( 3 mJ)

HARGLO-2: GLOW Signal LevelsEdge Channel 1 PMT Detected Counts

Gate On


Θ+−

=

Θ+−

=

+=

==

Θ

cos*

1*

)(

)(v

cos*

1*

)(

)(v

vv v

bygiven is vspeed windthe

,,,;2

1

ratios theand y sensitivit aGiven

degrees. ofelevation at EW,S,N, azimuths 4 from

obtained are from Edg2 and Edg1 signals Measured

y

x

2y

2x

SensRR

RR

SensRR

RR

where

WESNiEdg

EdgR

Sens

SN

SN

EW

EW

i

ii

1

2

3

4

5


Combined Molecular Sensitivity vs. T and vT= 150K to 350K , v = 0 to 100 m/s


0 10 20 30

Speed (m/s)

0

5

10

15

Height (km)

GLOWLoran Sonde

HARGLO-2 11/16/01 12:58Z

0 100 200 300

Direction (deg)

0

5

10

15

Height (km)

GLOWLoran Sonde


v

v

v

v v

v

v

gives Edg2 and Edg1 signals detected the in

noise shot the by dominated is s velocitiecomponent measured in error Assuming

v

v

v

v and

v

v

v

v

vv

v v

v

v v

by given is v, speed measured the

in error the ,v and v errors their andv, vs velocitiecomponent Given

y

x2

y

x

y

y

x

x

yy

xx

2

y x y x

⎟⎟⎠

⎞⎜⎜⎝

⎛+++⎟⎟

⎠

⎞⎜⎜⎝

⎛Θ+

+⎟⎟⎠

⎞⎜⎜⎝

⎛+++⎟⎟

⎠

⎞⎜⎜⎝

⎛Θ+

=Δ

+++Θ+

=Δ

+++Θ+

=Δ

=∂∂

=∂∂

⎟⎟⎠

⎞⎜⎜⎝

⎛Δ

∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛Δ

∂∂

=Δ

Δ

ΔΔ

SSNNSN

SN

WEWWEW

EW

SSNNSN

SN

WEWWEW

EW

EdgEdgEdgEdgSensRRRR



and


where

21

11

21

11

*cos*1

*)(

2*

...2

11

12

11

1*

cos*1

*)(

2*

21

11

21

11

*cos*1

*)(

2

21

11

21

11

*cos*1

*)(

2

2

2

2

2

2

2

22


0 2 4 6 8 10

Speed error (m/s)

0

5

10

15

20

Altitude (km)

Std dev all profilesShot noise error 12:58Shot noise error 13:30Shot noise error 14:01Shot noise error 14:33Shot noise error 15:04

Wind Errors - mcs0111161258Δz=200 m

0 5 10 15 20 25 30

Direction error (deg)

0

5

10

15

20

( )Altitude km


Q: How can we use ground based measurements to refine and validate future space based lidar system designs?

1) Validate the instrument performance behaves predictably versus measurable quantity (signal photocounts; signal to noise).

2) Establish reference system designs to examine impact of performance trades (e.g. spatial and temporal averaging schemes) or engineering trades

3) Scaling of ground based system performance to equivalent space-based system reveals where improvements are required and provide direction for technology and instrument system development programs

4) Scaling also provides a sanity check for space based designs


NS= number of laser shots atm()=1 way atmos transmission

A= telescope area a()= aerosol backscatter E= laser pulse energy m()=molecular backscatter= detection efficiency R= range to sample volumeopt= optical efficiency ΔR= range resolutionh= photon energy

Direct Detection Doppler Lidar SNR

NS EAopt atm2

() [a()+ m()]ΔR

hR2

SNR=sqrt


Wavelength 354.7 nmTelescope/Scanner Area 0.116 m2

Laser Linewidth (FWHH) 80 MHzLaser Energy/Pulse 25 mJ @ 50ppsEtalon FSR 12 GHzEtalon FWHH 1.7 GHzEdge Channel Separation 5.1 GHzLocking Channel Separation 1.7 GHzInterference filter BW (FWHH) 150 pmPMT Quantum Efficiency 22%

GLOW Lidar System Parameters-- June 21, 2005


GLOW System Efficiencies (6/21/2005)

Energy Monitor Channel

Edge Channels

Telescope/Scanner 0.26 0.26

FO Attenuation 0.82 0.82

FO Coupling 0.75* 0.75*

Interference Filter 0.42 0.42

Receiver Optics 0.93 0.90

Optical efficiency (w/o BS and Etalon)

0.083 0.080

BS 0.056 0.41

Etalon Trans (Mol. Edge)

-- 0.154

PMT PD 0.22 0.22

Total efficiency 0.001 0.0011* Estimated value. Includes Fresnel losses, boresight and alignment losses.


Comparison of Measured and Simulated SignalsJune 21, 2005

100 101 102 103 104 105 106

Detected Photocounts

0

5

10

15

20

Altitude (km)

Edge 1, 90 deg: Simulated Edge 1, 90 deg: Jun 21,2005Edge 1, 45 deg: Simulated Edge 1, 45 deg: Jun 21,2005

t= 10 sec

ΔR= 45 mE= 25 mJPRF = 50 pps


GLOW LOS Error Δz=0.5 km; t=1 min


Scaling GLOW to 400 km at z=10km

Ground Space Scaling factor parameters

Integration Time (s) 60 10 6

Δz/cos (km) 0.707 1.41 0.5

Laser Power J/s 1.25 W(50 Hz, 0.025 J)

30W(100 Hz, 0.3 J)

0.0417

Telescope area (m2) 0.116 0.75 0.155

Atmospheric transmission 0.2 0.95 0.21

Detector quantum efficiency

0.22 0.3 0.73

Optics transmission 0.06 0.30 0.2

Range to Target Volume (km)

14.14 551.6 1522

Scale factor product = 0.9


Edge Signals from 400 km


Simulated LOS Error from 400 km Δz=1 km; t=10 sec


Summary

• Ground based lidar measurements provide important insight into performance of future air and space based lidar systems– Measurements provide experimental validation of

atmospheric and instrument models– Inversion of lidar measurement performance can be

scaled to space for a single altitude/signal level – This information can be used to guide technology

development and explore sysetem trades for future designs


1.000e-8 1.000e-7 1.000e-6 1.000e-5 1.000e-42 3 4 5 2 3 4 5 2 3 4 5 2 3 4 5

Backscatter (m-1 sr-1)

0

5

10

15

Altitude (km)

MolecularAerosol

Model Backscatter Coefficient 355 nm


0.2 0.4 0.6 0.8 1.0

2 way atmos transmission

0

5

10

15

Altitude at 45 deg elevation

2-Way Atmospheric Transmission at 355nm


Incident Photon Count Rate


2-way atmospheric transmission


-60 -40 -20 0 20

0

5

10

15

Altitude (km)

GLOW Simulated wind error profile File: mcs0009251442 - 1.65 microsec; 600 shots

B. Gentry/GSFCSLWG 06/29/05 Scaling Ground-Based Molecular Direct Detection Doppler Lidar...

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