Preliminary comparison results of the October 2003 experiment with GroundWinds NH and NOAA's mini-MOPA lidar S. Tucker 1,2, I. Dors 3, R. Michael Hardesty 1, and Wm. Alan Brewer 1 Acknowledgements: A. Weickmann 1,2 and M. J. Post 4 ¹ Optical Remote Sensing Group Chemical Sciences Division (CSD) Earth System Research Laboratory ²Cooperative Institute for Research in Environmental Science University of Colorado, Boulder, CO ³University of New Hampshire, 4 Zel Technologies, LLC/NOAA, Working Group on Space-Based Lidar Winds Key West, FL, January 17-20, 2005

October 2003 Field Experiment NOAA’s mini-MOPA Coherent DWL GroundWinds New Hampshire DWL Occasional balloon-sonde launches NOAA’s 2005 Comparison and Validation Objectives Use analysis and comparisons to mini-MOPA data to: Verify GWNH performance –Ability to accurately measure wind profiles –Precision & accuracy (in stares and profiles) Check for improvements over GWNH 2000 data Verify photon count – extend to technological scaling to space. Quantify sensitivity improvements due to Photon Recycling

Additional Activities: Mini-MOPA Analysis Take advantage of long stare times in windy climate to study: –Sensitivity versus theoretical limit of the instrument –Effect of pulse duration on sensitivity –Extraction of mini-MOPA data at low SNR in the free troposphere –Pulse modeling –Turbulence profiling

Velocity Variance Estimation Methods Zeroth lag estimation: Mayor, et. al., J. Atmos. Oceanic Tech, 1997 Spectral noise floor estimation lags autocorrelation Autocovariance function at 1.26 km Range N lag ACF linear fit ACF Frequency (Hz) spectral amplitude Spectrum at 1.26 km range Spectrum at range 2 gate mean floor Brovko-Zrnic Cramer-Rao Lower Bound: Rye & Hardesty, IEEE Trans Geoscience & Remote Sensing,1993. UNH method: Standard deviation of 1 minute sliding window (5-6 samples at 10 s averaging times)

Wavelength9-11 micron Pulse Energy1-2 mJ PRF300 Hz Max Range18 km Scanning Full Hemispheric Precision10 cm/s Range Resolution m Mini-MOPA Doppler Lidar

CRLB: Rye & Hardesty, IEEE Trans Geoscience & Remote Sensing,1993. Mini-MOPA: Sensitivity versus theoretical limit of the instrument CNR dependent-minimum standard deviation values calculated using the linear fit to 0th lag of the ACF Black line: BZ-CRLB for these CNR values Square fill colors represent altitude according to the colorbar. Room for improvement?

Lags MOPA xcov MOPA 1  s Gaussian 1  s Autocovariance Function Mini-MOPA pulses: effect on velocity variance Pulse Shape

Variable Pulse Width & Accumulation Time

NOAA’s GWNH Validation Activities and mini-MOPA comparisons Verify MOPA’s usefulness as a comparison measurement Independent estimation of GWNH velocity variance –Range-independent variation removal –Photon-recycling vs. no Photon-recycling Comparison between GWNH and NOAA’s mini-MOPA lidar –Comparison of wind measurements –Comparison of turbulence measurements –Characterization of measurement biases –Characterization of systematic effects –Comparison of boundary layer performance LWG – Key West, FL January 17-20, 2005

Mini-MOPA wind profile validation MOPA profile:3:27:43 D MWO 10/31/03MOPA & Balloon-Sonde Wind Speed (m/s) Altitude (km) Balloon MOPA /31/03MOPA & Balloon-Sonde Wind Direction (deg.) Balloon MOPA

Mini-MOPA wind profile validation

Removal of GWNH offsets affecting all range gates (to improve precision estimates) 1.Take signal at each range gate & find linear trend. 2.Remove linear trend – left with variations about that trend. 3.Average the variations (not applicable in cases of strong turbulence)

Effects of NOAA/CSD-correction for instrument offsets

 v (m/s) Altitude (km) Standard Deviation vs. Altitude NH_ _M57 CSD-corrected linear fit ACF Uncorrected - linear fit ACF CSD-corrected Spectral noise floor Uncorrected - Spectral noise floor CSD-corrected 1 min std Uncorrected 1 min std (UNH method). UNH supplied Meas. Limit BW/  (N PED ) GW Variance estimates (photon recycled data) σ v estimates match UNH supplied measurement limit at altitudes above 6.5 km – Instrument/Camera limitations dominate Difference between UNH’s measurement limit and photon limit is described in UNH reports. sub 6.5 km results – Instrument and camera limitations cease to dominate. Other limitations?

 v (m/s) Altitude (km) Standard Deviation vs. Altitude NH_ _M57 CSD-corrected linear fit ACF CSD-corrected Spectral noise floor CSD-corrected 1 min std Uncorrected - linear fit ACF Uncorrected - Spectral noise floor Uncorrected 1 min std. UNH supplied Meas. Limit GW Variance estimates post-correction (PR) Uncorrected σ v estimates: ACF and Spectral methods more optimistic then 1 minute σ v estimates. BW/  (N PED ) Post-correction σ v estimates match UNH supplied measurement limit down to ~ 2km Near 2 km altitude errors due to presence of thin clouds.

 v (m/s) Altitude (km) Standard Deviation vs. Altitude NH_ _M57 linear fit 0 th lag ACF linear fit 0 th lag ACF PR UNH Meas. Lim UNH Meas. Lim PR   BW/(N PED ) BW/(N PED (PR)) (post-correction) σ v Ratios 1/  (PED ratio) Spectral noise floor ratio ACF 0 th lag est. ratio Measurement limit ratio 1 minute  v ratio P HOTON R ECYCLING : σ v Ratios Photon count ratios of ~2, ideally correspond to σ v ratios of ~0.71. Ratio of Photon Recycling (PR) to non PR σ v estimates vary around the ratios of UNH supplied measurement limits (usually 0.75 to 0.9) See UNH report regarding PR “quality factor”

Wind Profile Comparisons

Altitude (km)

Az =180 , GW Time:231.3 MOPA profile:231.7 Altitude (km) V est (m/s) Az =225 , GW Time:251.6 MOPA profile:252 V est (m/s) Az =270 , GW Time:271.7 MOPA profile:270.8 V est (m/s) Az =315 , GW Time:287 MOPA profile:286 V est (m/s) Az =0 , GW Time:302.4 MOPA profile:303.1 Altitude (km) V est (m/s) Az =45 , GW Time:316.7 MOPA profile:315 V est (m/s) Az =90 , GW Time:331 MOPA profile:323.3 V est (m/s) Molecular Molecular PR balloon MOPA projected MOPA Direct Single Az. Profile Comparisons for Molecular Channel

Stare Comparisons

Stare Comparisons: Offsets?

Summary Mini-MOPA performance is as modeled. MOPA data provides useful comparisons for low-level GW data. GWNH wind profiles generally compare well to those of MOPA and balloon-sonde data when clouds are not present. GWNH velocity variations approach the measurement limit modeled by UNH, however they are significantly higher than the theoretical detected-photon limit. UNH has attributed this degradation in velocity-variation, relative to the photon-limit, to receiver limitations. GWNH measurements show variable offsets relative to mini-MOPA and balloon-sonde data.

B. J. Rye, “Estimate optimization parameters for incoherent backscatter heterodyne lidar including unknown signal bandwidth,” Appl. Opt., 39, (2000). B. J. Rye, “Comparative precision of distributed backscatter Doppler lidars,” Appl. Opt. 34, (1995). R. Frehlich, “Estimation of Velocity Error for Doppler Lidar Measurements,” J. Atmos. Oceanic. Tech, 18, 2001, D. H. Lenschow, V. Wulfmeyer, and C. Senff, “Measuring Second- through Fourth-order Moments in Noisy Data,” J. of Atmos. Ocean. Tech., 17, , (2000). S. D. Mayor, D. H. Lenschow, R. L. Schwiesow, J. Mann, C. L. Frush, and M. K. Simon, “Validation of NCAR  m CO2 Doppler Lidar Radial Velocity Measurements and Comparison with a 915-MHz Profiler,” J. Atmos. Oceanic Tech., 14, 1997, B. J. Rye, R. M. Hardesty, “Discrete Spectral Peak Estimation in Incoherent Backscatter Heterodyne Lidar. I: Spectral Accumulation and the Cramer-Rao Lower Bound,” IEEE Trans Geoscience & Remote Sensing, 31, 1993, pp Assorted References LWG – Key West, FL January 17-20, 2005

miscellaneous

Stare Comparisons: Boundary Layer

Az =180 , GW Time:231.3 MOPA profile:231.7 Altitude (km) HV est (m/s) Az =225 , GW Time:251.6 MOPA profile:252 V est (m/s) Az =270 , GW Time:271.7 MOPA profile:270.8 V est (m/s) Az =315 , GW Time:287 MOPA profile:286 V est (m/s) Az =0 , GW Time:302.4 MOPA profile:303.1 Altitude (km) V est (m/s) Az =45 , GW Time:316.7 MOPA profile:315 V est (m/s) Az =90 , GW Time:331 MOPA profile:323.3 V est (m/s) Aerosol Aerosol PR balloon MOPA projected MOPA Direct Single Az. Profile Comparisons for Aerosol Channel

8 GWNH profile:03:40:30 MOPA profile:3:27:43 D MWO 10/31/03, GWNH with Photon Recycling _M110 Wind Speed (m/s) Altitude (m) Balloon MOPA GWNH-A GWNH-M

/31/03, GWNH without Photon Recycling _M110 Wind Direction (deg.) GWNH profile:03:40:30 MOPA profile:3:27:43 D MWO Balloon MOPA GWNH-A GWNH-M /31/03, GWNH with Photon Recycling _M110 Wind Direction (deg.) GWNH profile:03:40:30 MOPA profile:3:27:43 D MWO Balloon MOPA GWNH-A GWNH-M

GWNH Validation Activities GroundWinds –Sensitivity versus theoretical limit of the instrument for NH and HA systems –Sensitivity improvements made at GWNH since the LidarFest. –Total system transmission and recycling efficiencies –Technological scaling to potential airborne and space systems –Comparison of performance between the New Hampshire and Hawaii systems LWG – Key West, FL January 17-20, 2005

Distribution of (post-correction) σ v Ratios

Distribution of (no correction) σ v Ratios

Decreasing Pulse Width: Increased velocity variance & offset Velocity Estimate (m/s) Pulse Width (  s) Inconsistent CRLB fits and velocity offsets led to further investigation of the MOPA pulse formation process…

Mini-MOPA Pulse Formation: Block Diagram CW CO 2 Laser RF Discharge Optical Amplifiers ω0ω0 AOM MHz 12 Pass H(ω) output from AOMs FFT 6 Pass H(ω) AOM MHz FFT output from amplifiers x Lorentzian Gain, |H( ω )| frequency normalized gain x Lorentzian Phase frequency normalized phase Line center Pulse center

Mini-MOPA pulse modeling Exaggerated examples of asymmetric effect on velocity estimates frequency Normalized Amplitude 1 μs pulse Δf=0.1Mhz=-0.5m/s frequency Normalized Amplitude 500 ns pulse frequency Normalized Amplitude 500 ns pulse Δf=0.55Mhz=-2.5m/s frequency Normalized Amplitude 1 μs pulse 10 MHz

CNR (dB) CRLB MOPA 1  s Gaussian 1  s MOPA 500 ns Gaussian 500 ns Lags MOPA xcov MOPA 1  s Gaussian 1  s MOPA 500 ns Gaussian 500 ns Model with pulses at 10 MHz off amplifier line- center ACF CRLB Mini-MOPA pulses: effect on velocity variance

Mini-MOPA: Velocity Offset vs. Pulse Width Pulse Width ( μs) Velocity Estimate (m/s) range (km) 60 m pulse, vertical stare velocity estimates Average frequency monitor velocity estimate vs. pulse width