geoscience laser altimeter system aerosol and cloud observations by the glas polar orbiting lidar...
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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
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