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Update on Hybrid Detection DWL Study*

This paper discusses the importance of global wind observations, the results of Observing System Experiments (OSE) and Observing System Simulation Experiments (OSSE), and the current wind observing systems such as rawinsondes and scatterometers. It explores the potential for new wind observing systems, including UAVs and constant level balloons. The discussion highlights direct and coherent detection methods, their accuracies, and spatial resolution. The study also reviews the performance of hybrid detection systems in providing accurate wind data from space, contributing to numerical weather predictions.

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Update on Hybrid Detection DWL Study*

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  1. Update on Hybrid Detection DWL Study* G. D. Emmitt WG on Space-based Lidar Winds Oxnard, CA 7-9 February, 2001 *funded by the IPO

  2. Study Team • Bruce Gentry (GSFC) • Upendra Singh (LaRC) • Michael Kavaya (LaRC) • Gary Spiers (JPL) • Bob Menzies (JPL) • Dave Emmitt (SWA) PI

  3. Outline • Importance of global wind observations • OSE and OSSE results • Current wind observing systems • Accuracy, coverage and resolution • Role for Doppler wind lidars • Direct detection • Coherent detection

  4. PrimaryCurrent Wind Observing Systems • Rawinsondes (~ 1-3 m/s) • Surface stations (~1 m/s) • ACARS (~1 m/s) • Scatterometer (~2 m/s) • Cloud motion (5-7 m/s) • Water vapor motion (4 -5m/s) • Assimilating model’s first guess (~2-3 m/s)

  5. Potential new wind observing systems • Constant level balloons with dropsondes or DWLs • UAVs for targeted observations • Higher resolution water vapor winds (GIFTS) • GPS soundings…derived winds

  6. Data Utility • Most global wind information results from assimilating direct (t,q.u,v…) observations into numerical models • 4DVAR data assimilation becoming common • All observations must “compete” with other observations and model derived “first guesses” • Consequently the NWP community favors accuracy over coverage if trade is necessary • Spatial averaging < .1-.5 the model resolution (not necessarily the grid size) ~ 15 - 25 km averaging for today’s global research models

  7. Direct Detection • Photon counting • spectral bins or channels • edge filter • Broad molecular velocity spectrum • Narrow aerosol velocity spectrum • Instrument measurement accuracy is a function of #photons

  8. Coherent Detection • Heterodyne…frequency shift detection • Aerosol (and cloud particle) motions • Inherently accurate (<1 m/s) for SNR >2-5 dB • Data coverage is a function of threshold sensitivity (`10-30 coherent photons)

  9. Baseline Systems • Each concept is considered as SOA and is held to 250 watts for the laser subsystems and flown in a 400 km orbit • Non-scanning (for ease of comparison) with an along track product resolution of 200 km • LOSP Direct = 2.43 m/s at 3.5 km AGL • LOSP Coherent = .15 m/s at 3.5 km AGL • (90) for coherent system = 1.4 E-9 m-1sr -1

  10. Target Data Product • An LOSP with a normally distributed error of  = 1 m/s • Horizontal resolution: 100 X 100 km • Vertical resolution: 1 km (worst case) • Minimum swath width: 1300 km (50% coverage of equatorial band) • Useful data product obtained 90% of time from 3-4 km layer when intervening cloud fraction is < 50%

  11. Scaled Rayleigh System ORBIT EAP PWR Baseline 6.2 .25 KW 400 KM 2474 (400X) 25 KW* 833 km 6630 (1060X) 67 KW* * assumes a 2 meter telescope

  12. Scaled Coherent System ORBIT EAP PWR Baseline 2.4 .25KW 400 km 49 (20X) 1.2 KW* 833 km 118(49X) 3.0 KW* * assumes a 1 meter telescope

  13. Hybrid System Data Products(400 km orbit) Sub-system Resolution Soundings* LOSP  (km) (#) (m/s) Rayleigh 300 266 1.6 Coherent 100 1864 .71** * number of LOS soundings per orbit (may involve shot accumulation per sounding) **  (90) = 5.4 E-8 (6.8 E-8) m-1sr -1

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