CE370

Long Range Automatic Aerosol LiDAR

Remote sensing instruments

Overview

Features


Applications

The CE370 LiDAR provides key parameters like vertical aerosols and clouds distribution as well as boundary layer heights for the following applications:

        • Volcanic ash watch
        • Sand dust storm watch
        • Air quality monitoring and forecast
        • Climate change
        • Airport flight operation
        • Atmospheric sciences
        • Aerosol and cloud modeling
        • Numerical Weather Prediction (NWP)

User benefits

Enhanced measurement performance

        • Aerosol detection up to the stratosphere (typically higher than 24 km by night time)
        • Direct measurements  of the reference (532 nm) optical properties
        • Very short blind zone ( <50 m)
        • Automatic calibration of extinction (on molecular signal)

Real time analysis

        • Automatic extinction and backscattering profiles
        • Automatic calibration of aerosol concentration by coupling with CE318 photometer
        • Automatic stratification analysis
        • Real time "quicklook" visualizations

Enhanced reliability

        • 3 year operation without technical maintenance
        • Low maintenance cost
        • High stability even in outdoor operation (from -20°C to +45°C with optional thermal enclosure)

High flexibility of implementation

        • Eye safety compliance with EN-60825/ANSI Z136 (no need for airplane detection RaDAR that automatically shuts down the laser)
        • Automatic unattented operation
        • Easy transportation
        • Outdoor/indoor/mobile operation
        • Compliance for airborne operation

Technology

The CE370 is composed of a control unit (housing the laser and acquisition units) connected to a separated optical head system through 10 m long optical and electrical wires

Laser

      • 3 year life time without any maintenance
      • Integrated output power monitoring

 

Optical head system       

 

        • Galilean type optical heads
        • Large (200 mm) diameter for enhanced range
        • Long focal length (1 m) for enhanced range
        • Real mono-axis optical design: ensures  perfect alignment of emission and main reception
        • The low layer optical head(reception only), mounted on the front side of the main optical head, ensures measurements at very low distances (from 50 m)
        • The two optical heads are watertight and may be exposed to oudoor conditions

Acquisition unit

        • Detection in photon counting mode through a high quantum efficiency (QE), high counting rate avalanche photodiode

Operation

The system (control unit and optical head) is designed to operate between 15°C and 25°C. It can be used either indoor (in a temperature controlled room), or outdoor using the optional thermal enclosure, or in a mobile vehicle.

The optical head itself may be exposed to outdoor conditions.This may be useful for campaign operations or in mild climatic conditions.

The software performs automatic acquisition of the backscattered signal, data processing and real time visualization.

Measurement principle

        • 5000 times per second, the laser emits a light pulse that is scattered by the particles present in the atmosphere
        • A tiny part of the pulse light is directed backward towards the instrument (backscatter)
        • The time of flight of the pulse between emission and reception indicates the distance of the scattering particles
        • The amount of backscattered light received at each distance depends on the quantity and the type of the particles
        • The backscattered light is converted to an electronic signal (in the control unit) and then processed (on the PC) to deliver vertical profiles 

PC based data processing

The supplied software may be installed on any PC with recent Windows operating system.

It performs automatic signal acquisition and preprocessing

        • After pulse correction
        • Noise detection and correction
        • Overlap and range correction
        • Automatic detection of a reference (aerosol free) layer for automatic calibration of the extinction coefficient on the molecular backscatter

and real time analysis and visualization of the following parameters

        • Raw data
        • Range corrected signal (averaged over 1 min or more)
        • Extinction and backscattering profiles, optionally using external AOD/LiDAR Ratio data for automatic calibration
        • Planetary boundary layer detection
        • Vertical stratification analysis including cloud detection

Visulaization modes include both range profiles graphs and range-time color charts (Time series)

Volcanic ash plumes detection above the city of  Lille (France)  17-18 april 2010, Eyjafjallajökull eruption (Data provided by LOA )

Outputs

 

 

 

Time graph of background signal(top). Quicklook of PR2 (range corrected data) . Time chart of AOD & Angström coefficient (from external Sun Photometer) (bottom)

PR2 vertical profile (arbitrary unit) (left). Stratification quicklook (right)

Technical features

Specification

 

Parameter

Value

Source

Laser type

Frequency doubled Nd:YAG

 

Wavelength

532 nm

 

Pulse energy

10-20 µJ (option 30  µJ)

 

Repetition rate

5 kHz

 

Pulse width

<15 ns

Optics

External fiber optics length

10 m (30 m in option)

 

Main optical head type

Galilean

 

Main optical head aperture diameter

200 mm

 

Main optical head effective focal length

900 mm

 

Field stop

Double

 

Total beam divergence

Emission: 55 µrad

Reception : 55/ µrad (900 µrad for low range)

 

Beam configuration

Mono-axis. Bi-axis for low range

 

Eye safety

Yes (except for 30 µJ option)

Detection

Detector type

APD QE 55%.

 

Filter bandwidths (3)

0.2 - 2 - 10 nm

Power supply

Voltage and power

100/115/230 V AC , 28 V DC in option, <100 W

Data acquisition

Data acquisition mode

Photon counting.

 

Continuous acquisition

Yes, automatic

 

Data counting rate

25 Mc/s

 

Electronic range resolution

15 m gates

 

Electronic range

From 50 m up to 30 km (2048 gates).

 

Data transfer  to PC

USB

Measurement range*

Molecular detection range in typical conditions (AOD 0.2) with 10 min averaging

By night time: 24 km

By day time: 15 km

Retrieved products

PR2 / Ln(PR2) data (after instrumental corrections)

Yes

 

Stratification analysis

Yes: aerosols, boundary layers, clouds

 

Extinction & backscatter coefficients

Yes (with additional data : AOD or LiDAR Ratio)

Environmental conditions

Operation without thermal enclosure

Control unit: +20°C to +30°C, 0 to 90% RH

Optical head system:15°C to 35°C, 0 to 100% RH and rain

 

Operation inside thermal enclosure

-20°C to +45°C, 0 to 100% RH and rain

General

System transportability

Yes

 

Optical head dimensions

Ø 200 mm x 1300 mm

 

Control unit dimensions

L:700 mm x W 200 mm x H 400 mm

 

System weight

30 kg

*Measurement range

The detection range of a high altitude layer of particles (aerosols or cloud) strongly depends on its concentration.The more concentrated the layer, the farther its detection.

Therefore, to define the performance of a LiDAR in terms of measurement range, it is usual to rather refer to the Molecular Detection Range : the distance (in the absence of clouds) up to which the LiDAR is able to measure the small "molecular" signal of an aerosol free atmosphere (with a Signal to Noise Ratio superior to 1). This Molecular Detection Range only depends on measurement conditions (total aerosol loading, averaging time, night/day).

For any given measurement condition, the LiDAR will detect particle layers above the corresponding Molecular Detection Range, the maximal height depending on layer's concentration.

 

Implementation

Example of outdoor installation of the optical head system, Installation of the LiDAR with a Sun Sky Lunar photometer

Option

Thermal enclosure

      • Necessary for continuous outdoor operation
      • Houses the optical head system, and if needed the control unit

 

Specification

Value

Outdoor operation

YES

Outdoor temperature operation range

-20°C to +45°C

Relative humidity operation range

0-100% and rain

Power supply (max)

< 1000 W

Size

1000 x 1200 mm

 

H 2200 mm

Weight

350 kg