Geoscience Laser Altimeter System

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Aerosol and Cloud Observations by the GLAS Polar
Orbiting Lidar Instrument NASA - Goddard Space
Flight Center
Launched January 2003 Full Operations
September 2003
Ice, Cloud and Land Elevation Satellite
Geoscience Laser Altimeter System
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Surface Altimetry and Atmospheric Profiling
Surface Altimetry High Bandwidth, 10 cm, Strong
Signals Atmospheric Profiling Low Bandwidth, 30
m, Weak Signals gtgtgtgt Compatible System
Requirements
Surface Altimetry Requires Precise Cloud
Clearing Atmospheric Retrieval Requires Surface
Reflectance Measurement
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GLAS Transmitter and Receiver
Lasers Three Diode Pumped NdYAG Units 40 Hz
PRF 100 urad Beam Width 1064 nm - 65 mJ 532
nm - 36 mJ
Receiver One Meter Beryllium Mirror 1064 nm
(main surface channel) Avalanche Photodiode
Detector 1 gHz Surface Digitizer Channel 2 mHz
Cloud Digitizer Channel 532 nm (high
sensitivity atmospheric channel) 8 Geiger Mode
Silicon APD Modules 2 mHz Photon Counting
Channel
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GLAS Measurement Components
Atmospheric Profiles at 1064 and 532 nm S(z) C
E B(z) Te2(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
Surface Return Pulse at 1064 nm EsEo Te2 ? A/r2
Cp ? Te2 (zo) Surface Pulse Waveform Surface
Pulse Reflectance Vertical Resolution
15cm Signal Range - -100 to 300 m
Solar Background Radiance at 1064 and 532 P
I ? ?? A Sp Cb I
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West Antarctic - Siple Coast from ICESat
SIPLE COAST ICE STREAMS
Crary Ice Rise
Grounding line
SIPLE DOME
ROSS ICE SHELF
Ben Smith Univ. of Washington
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CLOUDS
Ive looked at clouds from both sides now..
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GLOBAL ORBIT LIDAR VIEWS OF CLOUD AND AEROSOL
DISTRIBUTION
FROM GLAS QUICK LOOK WEB SITE http//glo.gsfc.nas
a.gov/
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GLAS Data Visualization for October 3, 2003
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GLAS Observed Backscatter Cross Section and
Layer Heights Data Product Example (gla07,08, 09)
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Validation of Global Circulation Models (GCMs)
Detailed Comparison of GLAS And European Center
Weather Forecast Model
Boundary Layer Heights
Cloud Fraction
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Cloud Layer Count DistributionAll clouds

• Global cloudiness is 69
• Single layers account for 64 of cloudy cases
• Attenuation causes layer numbers to be
  undercounted
• Shape of distribution is typical

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31
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Maximum cloud height
01 Oct. 15 Nov. 2003

km

• 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.

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Zonal Cloud Top Frequency
01 Oct. 15 Nov. 2003
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.

AM and PM
PM
AM
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GLAS/MODIS Cloud Fraction Comparison

• 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.

Cloud fraction, zonal
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GLAS/MODIS Average Cloud Top Pressure Comparison
October, 2003
GLAS, PM
MODIS,AQUA
hPa
hPa

• 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

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Aerosols
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Dust of the Sahara
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GLAS Aerosol Optical Thickness
October, 2003
GLAS, 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.

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Global Aerosol and Boundary Layer Height
First Mapping of the Global Aerosol and Pollution
Capping Inversion Boundary Layer Height
GLAS Measurement of the Height of the Planetary
Boundary Layer October 2003
Model Output from European Center Forecast Model
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Geoscience Laser Altimeter System Application to
Aerosol Transport Models
GLAS 532 nm Data
Naval Aerosol Analysis and Prediction System
J. Spinhirne /GSFC January 2004
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GLOBE - Global Backscatter Experiment Definition
of Space Lidar Requirements

• 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

Menzies, Tratt, Spinhirne and Hlavka - JGR 2002
.
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South Africa Smoke Aerosol
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Breon et al., GRL in press, 2005
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GLAS STATUS

• 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/

Laser Diode Failure
Laser Contamination
Severe Contamination
Laser Doubler Failure
2005 Feb. 20 Mar. 25 May 18 June 22
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