2-Micron high-repetition rate laser transmitter for coherent DIAL measurements of atmospheric CO2

Transcription

1 2-Micron high-repetition rate laser transmitter for coherent DIAL measurements of atmospheric CO2 Fabien Gibert, Dimitri Edouart, Claire Cénac, Florian Le Mounier, Pierre H. Flamant Laboratoire de Météorologie Dynamique Institut Pierre et Simon Laplace Equipe Lidar, Atmosphère, Biosphère & Climat (ABC)

2 Needs on Carbon dioxide and Climate issue Better understanding of climate change direction in near future is based on assessment of carbon sources and sinks strengths with time and locations and atmospheric CO2 fluxes Monthly CO2 fluxes at global scales call for accurate and evenly distributed CO2 concentration that in turn call for remote sensing techniques (passive and active) for flexibility to overcome inherent sparse and limited deployment of surface network, TCCON sites and airborne flask measurements Active remote sensing technique i.e. DiAL technique in space is promising for GHG such as CO2 but it requires further airborne and ground based studies and key technology demonstration Geo-science engineering i.e. CO2 geological sequestration sites, as viable solution wrt climate change issue call for demonstration with limited and manageable hazard issues Basic science question such small scale CO2 flux and scale integration still need dedicated studies with appropriate tools In this context, the ABC(t) team is contributing to several areas in developing i) a flexible transportable CO2 and Wind lidar for field campaigns and ii) a new laser transmitter based on a pump fiber laser and multiple fiber components for both heterodyne and direct detections 2

3 CO2 concentration - Sentinelle project First sequestration site for CO2 in Lacq, France CO2 global budget (-5000 m 2000 m) Measurement campaign: March 2012 FTIR In situ sensors Dial LiDAR high-pressure CO2 3

4 Measurement specifications Science requirements: High temporal/spatial resolution 3D measurements: range resolved using distributed scatterers and LOS scanning Monitoring: simultaneous wind velocity and CO2 mixing ratio measurements Fluxes: combined wind velocity & CO2 mixing ratio measurements using eddy correlation technique Monitoring Flux Spatial resolution 150 m 150 m Temporal resolution 1 min 10 s 0.5 m/s 0.5 m/s 4 ppm 10 ppm Wind velocity accuracy CO2 concentration accuracy 4

5 COWI/g set-up Telescope CW Local Oscillator Tm fiber pump laser 2 µm pulsed laser Free space cavity Detection Injection Detection Reference 5

6 Optimisation of laser transmitter for heterodyne detection 1 - Efficiency: Energy per pulse P CNR = >1 Pnoise 2 Optimisation of the number of independent samples σ ( ρ CO 2 ) t / PRF 3.10 CNR at furthest range of interest 2 khz < PRF < 4 khz 6

7 Master oscillator output frequency 1- Ramp & fire injection seeding: set-up 1939 nm CW Tm Fiber laser D CW Tm, Ho laser Resonance peaks Ho:YLF Lyot Vpzt Master oscillator at 2051 nm AOM P (W) Free-space cavity 7 D Heterodyne signal

8 Master oscillator output frequency 1- Ramp & fire injection seeding: results 20W - 2 khz -> 1 mj 130 ns Peak detection gate PZT Q-switch gate Resonance peak SLM laser pulse 8

9 Master oscillator output frequency 2 Pound-Drever-Hall injection seeding: set-up CW Tm Fiber laser Vpd 20 MHz EOM PDH ε D CW Tm, Ho laser Resonance peaks Ho:YLF ε PI Vpzt Power oscillator at 2051 nm Lyot P (W) AOM Free-space cavity 9 D Heterodyne signal

10 Master oscillator output frequency 2 Pound-Drever-Hall injection seeding: results Vpd CW mode Lock on resonance peak Dithering excursion : Δν = 3 MHz Recorded beat signal ε Vpzt Vpzt Q-switch mode Lock on resonance peak Hold-off Dithering excursion: Δν = 1.5 MHz Q-switch gate Laser pulse 10

11 Real-time acquisition and processing by FPGA (Field Programmable Gate Array) : set-up Benefits: high PRF acquisition real-time pre-processing: data set reduction Tasks: real-time spectrums means FIFO 1 Apodisation Rectangle Hanning FFT Spectrum MUXs Switch ON/OFF ON Means OFF 11 FIFO 3

12 Conclusion Best lidar operation according to trade-off between pulse energy, pulse duration and pulse repetition frequency for optimal DIAL and wind measurements accuracies MO performance: 2 khz, 1 mj injection seeded thanks to the ramp and fire technique Future works: - DFBs amplified by TDFA set-up will be tested for injection seeding - Implementation of PDH locking technique in Q-switch mode - FPGA tests in real operation - Laboratory tests in October st field campaign for transportable lidar in March