Geoscience Laser Altimeter System

Aerosol and Cloud Observations by the GLAS Polar Orbiting Lidar Instrument

NASA - Goddard Space Flight Center

Launched – January 2003Full Operations – September 2003

Ice, Cloud and Land Elevation Satellite

Surface Altimetry and Atmospheric Profiling

Surface Altimetry – High Bandwidth, 10 cm, Strong SignalsAtmospheric Profiling – Low Bandwidth, 30 m, Weak Signals

>>>> Compatible System Requirements

Surface Altimetry Requires Precise Cloud ClearingAtmospheric Retrieval Requires Surface Reflectance Measurement

GLAS Transmitter and Receiver

Lasers: Three Diode Pumped Nd:YAG Units40 Hz PRF 100 urad Beam Width1064 nm - 65 mJ532 nm - 36 mJ

Receiver: One Meter Beryllium Mirror1064 nm (main surface channel)

Avalanche Photodiode Detector1 gHz Surface Digitizer Channel2 mHz Cloud Digitizer Channel

532 nm (high sensitivity atmospheric channel)

8 Geiger Mode Silicon APD Modules2 mHz Photon Counting Channel

GLAS Measurement Components

Solar Background Radiance at 1064 and 532 P = I A Sp = Cb I

Surface Return Pulse at 1064 nmEs=Eo Te

2 A/r2 = Cp Te2 (zo)

Surface Pulse WaveformSurface Pulse Reflectance

Vertical Resolution – 15cmSignal Range - -100 to 300 m

Atmospheric Profiles at 1064 and 532 nmS(z) = C E B(z) Te

2(z) /r2

Aerosol and Thin Cloud:532 nm – GAPD Photon Counting

Denser Cloud:1064 nm – Analog APD

Vertical Resolution – 75 m (20 m)Horizontal Resolution - ~ 175 m (500m)Signal Range - -5 to 40 km

Ben Smith Univ. of Washington

Crary Ice R

iseGrounding line

ROSS ICE SHELF

SIPLE C

OAST ICE S

TREAMS

SIPLEDOME

West Antarctic - Siple Coast from ICESatWest Antarctic - Siple Coast from ICESat

CLOUDS

I’ve looked at clouds from both sides now…..

FROMGLAS QUICK LOOKWEB SITE: http://glo.gsfc.nasa.gov/

GLOBAL ORBIT LIDAR VIEWS OF CLOUD AND AEROSOL DISTRIBUTION

GLAS Data Visualization for October 3, 2003

GLAS Observed Backscatter Cross Section and Layer Heights Data Product Example (gla07,08, 09)

12

8

4

km

km

km

Latent Heat Flux

Sensible Heat Flux

ECMWF PBLGLAS PBL

Validation of Global Circulation Models (GCM’s)

Detailed Comparison of GLAS And European Center Weather Forecast Model

Boundary Layer Heights

Cloud Fraction

Cloud Layer Count DistributionAll clouds

01 Oct. – 15 Nov. 2003

45%

31%

17%

•Global cloudiness is 69%

•Single layers account for 64% of cloudy cases

•Attenuation causes layer numbers to be undercounted

•Shape of distribution is typical

Maximum cloud height

http://wikimediafoundation.org/wiki/

km

PSC•Maximum cloud height in each cell over the observation period.

•Some features: warm pool; tropical central Africa; Carribbean; western coasts of the continents.

•Line plot shows the zonal maximum cloud height; note polar stratospheric clouds.

01 Oct. – 15 Nov. 2003

Zonal Cloud Top Frequency

01 Oct. – 15 Nov. 2003

AM and PM

PMAM

0.5 km vertical bins•Top shows results from all observations•Two lower images show the comparison between the AM and PM observations.•Differences are the increase in the convective influence in the PM, with a lessening of the influence of the low clouds.

GLAS/MODIS Cloud Fraction Comparison

October, 2003GLAS, PM MODIS,AQUA

Percent Percent

Cloud fraction, zonal

GLASMODIS

•Features in the expected locations. High cloud fraction the the ITCZ and north and south circumpolar regions. Low cloud fraction in deserts.

•GLAS finds significantly more cloudiness in the deserts regions.

•Zonal cloud fraction display shows excellent agreement between the two

instruments except in the polar regions.

GLAS/MODIS Average Cloud Top Pressure Comparison

October, 2003GLAS, PM MODIS,AQUA

Zonal cloud top pressure

GLASMODIS

hPahPa

•GLAS results show higher clouds

•GLAS finds geometrical cloud top; MODIS finds thermal cloud top

•Other factors such as sampling differences are needed to explain large difference

Aerosols

Dust of the Sahara

GLAS Aerosol Optical Thickness

GLASMODIS

October, 2003GLAS, PM MODIS,AQUA

OD OD

•Qualitative agreement in location of many persistent features

•GLAS misses transient features such as California fire because of sampling.

•GLAS retrieves generally lower OD because of a low bias in extinction to

backscatter ratio.

Global Aerosol and Boundary Layer Height

First Mapping of the Global Aerosol and Pollution Capping Inversion ‘Boundary Layer’ Height

Model Output fromEuropean CenterForecast Model

GLAS Measurement of the Height of the Planetary Boundary Layer – October 2003

Geoscience Laser Altimeter SystemApplication to Aerosol Transport Models

J. Spinhirne /GSFC January 2004

GLAS 532 nmData

Naval Aerosol Analysis and Prediction System

• Observe backscatter cross sections below 10-7 (1/m-sr) for aerosol transport

•Observe backscatter cross sections up to 10-3 for dense aerosol events • Observe backscatter cross sections over six orders of magnitude including clouds

GLOBE

GLOBE - Global Backscatter ExperimentDefinition of Space Lidar Requirements

Menzies, Tratt, Spinhirne and Hlavka - JGR 2002

.

South Africa Smoke Aerosol

Breon et al., GRL in press, 2005

• Global lidar data are a fundamentally new measurement from space for global aerosol and cloud

cover.

• GLAS data results have fully validated the science, technology and observation strategy and meet

the objective of profiling all radiatively significant cloud and aerosol layers.

• GLAS Data products are in open release to the science community.

Quick look and data visualization: http://glo.gsfc.nasa.gov/

Full Data Access: http://nsidc.org/daac/

GLAS STATUS

GLAS Observation PeriodsObservation

Period Laser 532 nm 1064 nmFeb 20 – Mar

28 2003Sep 25 – Nov

18 2003Feb 17 – Mar

21 2004May 18 – Jun

21 2004Oct 03 – Nov

07 2004

1

2

2

2

3

None

Excellent

Excellent - Good

Excellent

Excellent

Excellent - Good

Fair (Night Only)

Poor (Night Only)

Fair

Excellent

Laser Diode Failure

Laser Contamination

Severe Contamination

Laser Doubler Failure

2005: Feb. 20 – Mar. 25 May 18 – June 22