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GWOLF and VALIDAR Comparisons

This article discusses the Lidar Intercomparison Facility at NASA/LaRC and its use for intercomparisons of VALIDAR and GWOLF lidar systems. The facility features target lights, paved parking lot, and utilities for data collection and validation experiments.

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GWOLF and VALIDAR Comparisons

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  1. GWOLF and VALIDAR Comparisons M. Kavaya & G. KochNASA/LaRC D. Emmitt & S. Wood SWA Lidar Working Group Meeting Sedona, AZ 27-29 January 2004

  2. Outline • NASA/LaRC’s Lidar Intercomparison Facility • VALIDAR • GWOLF • VALIDAR intercomparisons • Hard target experiments • Cloud returns • Vertical motion

  3. Lidar Intercomparison Facility (LIF) at NASA Langley Research Center

  4. Lidar Intercomparison Facility • Features: • Inside NASA grounds • Paved parking lot for up to 4 lidar systems • Row of surveyed marks on parking lot with 32-foot spacing • Row of 4 target lights on tall structure with 32-foot spacing • Surveyed positions of lidars and targets allows for parallel alignment among the lidars • Target lights at 677-m range, and 6° elevation angle • Target lights atop poles allowing atmospheric data collection while aimed at lights • Utilities available including telephone, intercom, internet, and electrical power

  5. VALIDAR & GWOLF at the Lidar Intercomparison Facility Location Of Target Lights Bldg 1297 R-B-Y-G

  6. View Of Lidars From The Target Lights’ Location Location Of Lidars Bldg 1159

  7. Lidar Intercomparison Facility • Possible Enhancements: • Lidar aim compensation for differing beam departure heights • Calibrated flat targets mounted on flat structure or at ground level for horizontal path • Calibrated velocity moving targets (> ? m/s) • Detectors near the target lights to confirm lidar aiming • Ancillary in situ and/or lidar sensors

  8. Validar • Objectives: • Demonstrate advanced 2-mm lidar components in a complete lidar • system. • High-energy lasers, receiver optics, detectors, and electronics are • being developed at LaRC from a variety of funding sources. Validar • serves as a testbed for this development. • Make field measurements as required for validation. • FY ’04 Specifications are • - laser pulse energy = 100 mJ (78 mJ) • - pulse repetition rate = 5 Hz (10 Hz) • - pulse width = 150 ns • - wavelength = 2053.5 nm

  9. Lidar Specifications FY 02 FY 03 FY 04 (water cooled) (cond. cooled) (cond. cooled) pulse energy 30 mJ 83 mJ (65 mJ) 100 mJ (78 mJ) pulse rep. freq. 5 Hz 5 Hz (10 Hz) 5 Hz (10 Hz) wavelength 2050.8 nm 2050.8 nm 2053.5 nm pulse length 180 ns 150 ns 150 ns spectrum single freq. single freq. single freq.

  10. Validation Lidar Facility VALIDAR Trailer Data Analysis & Visitors Rooms Lidar System

  11. Validation Lidar Facility • Validation Lidar (VALIDAR) Facility: • Well-instrumented 48 ft long Trailer • Hemispherical Scanner with 20 cm effective aperture • Elaborate Video System consisting of 2 sets of cameras, monitors, and recorders • Weather Station • GPS Receiver • Powerful state-of-the-art Coherent Doppler Lidar • 50-150 mJ, 5-10 Hz, Diode-pumped Transmitters • 10 cm COTS and 25 cm SPARCLE Telescopes • Real-time data processor and display

  12. GWOLF(Groundbased Wind Observing Lidar Facility) • Funded by IPO as part of NPOESS development of cal/val program for space based wind observing systems such as QuikScat, WindSat, CMV, WVMV and future DWLs • Currently the TODWL system mounted in a trailer; plan to replace TODWL scanner with a roof mounted hemispherical scanner.

  13. Validar/GWOLF Comparisons • Performed at LaRC’s LIF • Horizontal and vertical stares • 200m resolution for Validar • 1 minute averaging

  14. GWOLF hard target and threading • Performed at LaRC’s LIF • Using corrugated metal enclosed elevator shaft at 677 meters from lidar as hard target • 100 meter range gates • 5 peak threading

  15. Cloud returns • Performed at LaRC’s LIF • Objective is to understand how to process and interpret GWOLF returns from cloud boundaries (large ~ 15 -20 dB backscatter gradients)

  16. Vertical velocity from VADs • Performed at LaRC’s LIF • Question is “ How accurate and reliable is the estimate of the vertical velocity using the offset in the sine fit of a partial VAD” • Interweaved a 25 second vertical stare into a 7 point partial VAD.

  17. Summary • The LaRC’s Lidar Intercomparison Facility enables long term, iterative evaluation of specific lidar performance issues. • Cloud boundary returns, hard target (ground surrogate) returns, instrument stability and low SNR signal processing investigations • Plan is to bring direct detection systems to LaRC for detailed investigations of both individual as well as hybrid wind sensing issues.

  18. Clouds • Backscatter values based upon backscatter data at wavelengths other than 2 microns • Modeled to 2 microns (rather wavelength independent) • Cirrus (0 to -37 C): 7.0 E-5 m-1sr-1 • Warm, opaque: 1.8 E-5 m-1sr-1

  19. TODWL 03 Per hard target calibration Per current theory

  20. Cirrus at 5800 m agl

  21. Lidar Design

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