LIDAR TECHNOLOGIES FOR EARTH OBSERVATION January 2008 Dr Kim Hampton Lidar Technologies Ltd. khampton@hovemere.com.

LIDAR TECHNOLOGIES FOR EARTH

OBSERVATION

January 2008

Dr Kim HamptonLidar Technologies Ltd.

khampton@hovemere.com

Lidar

• Atmospheric Lidar– Range resolved (multiple range measurements)– No hard target needed– Elastic backscattering

• Aerosols (Mie)• Wind (Mie, Rayleigh)• Chemicals (DIAL - Differential Absorption Lidar)

– Inelastic backscattering (for chemicals mainly)• Raman Lidar • Resonance Lidar• Fluorescence Lidar

• Range Finder/ Altimeter– Single precise range measurement – Require hard target

• Sounder– Range resolution sacrificed (secondary property)– Require hard target– Chemical concentration integrated over the total column

LaserBeam Conditioning

Telescope

Detector

Filter/SpectralAnalysis

Data Acquisition

Clouds

Data Products

AerosolsMolecules

Basic Lidar Components

Power * ApertureProduct [W*m2]

Power * ApertureProduct [W*m2]

Power – Aperture Product

Atmospheric Lidar

> 10 W.m2

Atmospheric Lidar

> 10 W.m2

Sounder

3 ...10 W.m2

Sounder

3 ...10 W.m2

Altimeter

< 1 W.m2

Altimeter

< 1 W.m2

ignore atmospheric signal

increase range resolution

reduce size and power

limit range resolution

limit spatial resolution

use DIAL

Imaging Lidar

<< 1 W.m2

Imaging Lidar

<< 1 W.m2

short range

scanning

UV

IR

NIR

UV

Applications

• Cloud top profiling

• Aerosol monitoring

• Pollution monitoring

• Wind measurement

• Surface mapping

• Vegetation canopy thickness

• 3D imaging for landing, docking and formation flying

What a Satellite Lidar Can/Cannot Do

Measure wind

Measure gas concentration

Measure altitude

Measure vegetation canopy thickness

Build 3D elevation map

Measure fluorescence

Cover large area (10km)

Measure in a small spot 10m (>100m)

Be small and cheap

Lidar Missions

• Extensive experience in NASA – Multiple altimeter missions – Earth, Moon, Mars, Mercury, Asteroids– Atmospheric measurements from space – GLAS, CALIPSO

• ESA gathering speed– AEOLUS (ADM) - first space wind lidar– ATLID (EarthCARE) – aerosol and cloud monitoring

• Future– MESOSPHERE– Imaging Lidar for Mars / Moon Landing and Rendezvous and Docking– A-SCOPE (sounder, CO2 monitoring)

Lasers For Space Lidars

• Lasers are the most critical component

• Primary concerns

– Reliability (at least two lasers needed)

– Wallplug efficiency

• High pulse energies needed (10 – 150 mJ)

– Large distance

– Limited integration of multiple measurements due to high speed

• Short pulses needed (ns level)

– 1-5 ns for altimeters

– 10-20 ns for atmospheric Lidars

– 50-100 ns for sounders

Prospective Laser Technologies

• Under development by ESA and NASA

– Diode Pumped Solid State Lasers – atmospheric Lidars, altimetry– Microchip Lasers – altimetry, imaging Lidars– Fibre Lasers (MOPA) – sounders, altimetry– Femtosecond lasers – metrology

• Target wallplug efficiencies – 15 - 30 %

Filters For Lidars

• Critical for atmospheric Lidars– Atmospheric Lidars – pm level bandwidth required– Altimeters - < 1 nm bandwidth– Sounders - ~ 1nm bandwidth

• Solutions– Free space only, single mode fibre coupling not applicable– Fabry-Perot Etalons (Hovemere Ltd, UK)– Interference filters (Barr, USA)

• Capacitance Stabilised FP Etalons– Space Qualified, UV filter for ATLID developed – <1 pm bandwidth with transmission of > 70 % (!)– Finesse F=33 (and F>100 demonstrated)

Detectors for Lidars

• External photo effect– Photomulltipliers (PMT), Microchannel plates (MCP) – Preferred in the UV, relatively low QE – Very low noise, very high speed (sub ns), no dead time– High voltage, can die from over illumination, degrade with time– Best for atmospheric Lidars

• Internal photo effect– Avalanche Photo Diodes (APD)– Preferred in the IR, high QE– APDs for 1064nm to 2050nm now being developed– Low control voltage, cooling required– High noise, can be sensitive to radiation, have dead time– Best for altimeters and sounders

Prospective Detectors Technologies

• Geiger Mode Si APDs – sensitive to blue and green + some UV– high speed ~ 100ps, low voltage ~ 30V– easy to make in array format– respond to a single photon only (the rest are lost)– dead time can be more than 50 ns

• IR APDs– InGaAs APD (1.5 um and 2 um) presently being developed– MCT APD (1.5 um and 2 um) to be developed soon by ESA

• EM CCDs– high QE, high sensitivity

UK Capabilities in Lidars

• Composite materials – Light weight structures for mirrors, telescopes, optical benches

• Leading PMT, MCP and IR APD detectors– PMT, MCP, InGaAs & InAlAs proven, MCT (?)

• Photonic Crystal Fibres– Lasers, Gas filled calibration references, Multimode fibre Bragg Gratings

• Advanced Lidar Detection Chain– Optical Filters, Altimetry, Data processing

• Imaging Lidar for Mars/Moon landing– 3D imaging for hazard avoidance starting from several km

• Hollow wave guides – IR Lidars reducing mass of bulk optics, compact on chip solution

• Mini satellite platforms– Possible lower orbit, possible formation flying

Hard Technical Questions

Contact:

• Dr Mike Foster or Dr Ivelin Bakalski

– mfoster@hovemere.com– ibakalski@hovemere.com