Remote Observations of the Electric Field within Thundercloud: New LIDAR - Based Techniques The real time measurement of spatial and temporal distribution of the electric field in and around thunderclouds is important for understanding the formation mechanisms of thunderclouds, for predicting the appearance of lightning strokes and for understanding the processes of the cosmic ray electrons acceleration and the bremsstrahlung photons generation caused by the electric field of clouds. Now the electric field meters, used for this purpose, are set on Earth surfaces or installed on balloons. These techniques are limited as they typically provide a single sample at discrete altitudes at one time. LIDAR systems are the main instrument which allows to realize real time remote measurement of the electric field strength and direction with high spatial and temporal resolution. LIDAR systems are based on the absorption and/or scattering of light by the gas, liquid or solid
21
Embed
Remote Observations of the Electric Field within Thundercloud: New LIDAR - Based Techniques The real time measurement of spatial and temporal distribution.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Remote Observations of the Electric Field within Thundercloud:New LIDAR - Based Techniques
The real time measurement of spatial and temporal distribution of the electric field in and around thunderclouds is important for understanding the formation mechanisms of thunderclouds, for predicting the appearance of lightning strokes and for understanding the processes of the cosmic ray electrons acceleration and the bremsstrahlung photons generation caused by the electric field of clouds. Now the electric field meters, used for this purpose, are set on Earth surfaces or installed on balloons. These techniques are limited as they typically provide a single sample at discrete altitudes at one time. LIDAR systems are the main instrument which allows to realize real time remote measurement of the electric field strength and direction with high spatial and temporal resolution. LIDAR systems are based on the absorption and/or scattering of light by the gas, liquid or solid state. Atomic and molecular spectra can be measured very accurately and sensitively using spectroscopy techniques.
Scattering of Electromagnetic Waves
EM wave induced dipole moment
Linear Nonlinear
P ~ χ (1)E + χ (2)E1E2 + χ (3)E1E2E3 + …
Elastic
Non Elastic
GeometricMie
ReyleighBack Raman
Fluorescence
Four Wave Mixing
P ~ χ (3)E1E2E3exp{ i [ΔKr – Δωt ]} ω = ω1 – ω2 + ω3
K = K1 – K2 + K3
I ~ │χ(3)│2 I1I2I3
Four Wave Mixing & Electric Field
1. Difference Frequency Generation
P ~ χ (3)E1E2E ωE = ω3 = 0 => ω = ω1 – ω2
K = K1 – K2
I ~ │χ(3)│2 I1I2E2
Experimentally realized (laboratory)!!!
2. Sum Frequency Generation
P ~ χ (3)E1E3E ωE = ω2 = 0 => ω = ω1 + ω3
K = K1 + K3
I ~ │χ(3)│2 I1I3E2
Experimentally realized (laboratory)!!!
V. N. Ochkin et all. 19951atm, 532nm, 683nm
H2 – 2.4 μm => 20V/cm
Second and Third Harmonic Generation & Electric Field
Electric Field Induced Second harmonic generation (EFISH)
Nonlinear spectroscopyAdvantages:Direct measurement of the electric field.High spectral resolution (Limited by laser line-widths).Disadvantages:Required two laser sources.Registration of IR signal (required fast IR detector for spatial and temporal resolution).Strong absorption of the IR radiation by water (required additional investigations).Development for other molecules, atoms, charged molecules, ions, isotopes etc.Development of Nonlinear spectroscopy techniques for remote sensing in situ.
Linear Spectroscopy Advantages:One laser sourceDisadvantages:Electric field measurement via its influence on the spectrum of gases (not direct).Required high resolution spectrometer, including IR.Required large aperture receiving optics.Required (in some cases) high power IR laser.
The electric field remote sensing methodology in thunderclouds need additional investigations and development !!!
Development of Atmospheric Polarization LIDAR System
The green points are the separated cross-polarized beams.
Laser Emitter and Receiving Optical System Alignment
Alignment Laboratory Stand
By means of the laboratory stand was aligned: The Laser, including, laser oscillator and laser amplifier. The Laser with Beam Expander (14X). Diode Laser beam with its beam expander (200X). Diode Laser beam optical axis with RT housing tube axis. Receiving Telescope (RT) mirror optical axis with Diode Laser beam optical axis and RT housing axis. Polarization Separator (PS) optical axis with RT Mirror optical axis. PS with cross-polarized beams outputs and RT mirror focus. Signal transportation fibers with cross-polarized beams. Adjustment of PMTs for registration of GLD beam.
The YerPhI LIDAR System
The Laser
Laser Beam Expander
PMTs
Aiming Optics
Receiving Telescope
Laser Cooling Pipes
Flash-lamp Supply Cables
Q-Switch Driver Cables
Laser Emitter Alignment
System Triggering Photodiode
Signal and Supply Cables
LIDAR System
Polarization Separator
Optical Signal Transportation Fibers to PMTs
The Laser
Laser Beam Expander
Receiving Telescope
Laser Emitter Alignment Mount
Polarization Separator
Alignment Mount
PMTs
Registration System
Triggering Photodiode
Stepper Motor
Stepper Motor end Switch
Play-free Gear
Optical Filter Boxes
Laser Emitter Alignment
Registration System
Triggering FiberAiming Optics
Optical Signal Outputs
Laser Emitter Output Energy Control Fibers
Receiving Mirror Focus Finder
The LIDAR Registration and Control System
Triggering Pulse (5nsec/div).
System Triggering PD and its electronics
PMT Power Supplies
PD and PMT Amplifier Power Supplies
NI DAQ BNC Inputs and Outputs
NI USB DAQ
Oscilloscope 500MHz
LIDAR Controllable Parameters
LE beam 1064nm output energy. LE beam 532nm output energy. LE beam repetition rate. LE Q-Switch driver pulse delay. LE beam polarization finder. PS – LE beam polarization angle. Registration delay. LE – RT angle. PMT supply voltage. LIDAR azimuth and elevation. LE cooling temperature.
Laser flash-lamp background and Reflected from a wall signal (250m).Horizontal - 30m/div;Vertical signals - 0.1V/div;Vertical trigger - 2V/div;PMT - 0.5kV.
First Backscattered Signal Observations
Scattering from Atmosphere and Clouds. (Hor.-750m/div; Ver.-20mV/div; PMT-2kV; PS-90deg).
First Backscattered Signal Observations
Scattering from Atmosphere and Clouds.Horizontal - 750m/div;Vertical - 50mV/div; PMT - 2kV; PS ~ 45deg).