LIDAR, episode 4 A NEW HOPE

LIDAR, Episode IVTHE PURSUIT OF DATA David Colucci Derek Burke

TheoryLaser fired into atmosphereVaried return based on backscatter from clouds/aerosol etc.Time measured from pulse fired to backscatter return is used to calculate cloud height and other valuesReturn signal is diminished according to inverse square law and needs to be normalized

Cover the power output of the laser and considerations of wattage considering safety

Major return due to clouds, dwindling aerosol return

Height is found by cutting the time from pulse to return in half (because of travel and return) and multiplying by the speed of light

Normalizing includes multiplying by square of height this however accentuates noise2

Applications

Valuable as a ceilometer at airportsVolcanic ash warning system for aircraftUsed to study atmospheric aerosol ->

Courtesy of NASA4Time Lapse Photography

Bust out the vaisalia data6

Lidar Development: Phase IEntry level including the major components just to test the basic concept.

Simple laser pointer aimed at ceiling (green)Lens to focus returnFilter to cut returnPhotodiode andRead signal in voltage on fluke-meter

7Board for photodiodeOp amp 410 MHzGain increased by Resistor valueAmplifies signal from the diodePhotodiode connects to triport on back of board with use of 10nm filter

Board in OperationFor the amplifier, a positive and negative voltage are pulled.The signal out is shown as the white wireSignal is read on the voltmeter

9Lidar Development Phase IIBegin the full scale implementation of a lidar device.Photodiode/Filter UPGRADED100mm active area photodiode with BNC mount532nm Filter with 2nm toleranceSM tube assembly

LASER532nm, 100 mW outputQ-switched adjustable pulse frequencySafety doesnt take a vacation

Triggering the ScopeWe needed the scope to start acquiring when the laser firedThe external trigger on the laser driver gave a faint square wave that followed the laserWe amplified and filtered this signal to trigger acquisitionCircuit shown