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Validation of Satellite Borne Lidar Systems by Ground Based and Airborne Instruments

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LITE = Laser In Space Technology Experiment. On space shuttle flight STS-64, Sept. 9 to 20, 1994 ... the 532 nm data is shown for October 6. The track starts ... – PowerPoint PPT presentation

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Title: Validation of Satellite Borne Lidar Systems by Ground Based and Airborne Instruments


1
Validation of Satellite Borne Lidar Systems by
Ground Based and Airborne Instruments
  • Patrick Hamill, San Jose State University
  • Jens Redemann, BAER Institute

Popayan, Colombia, July 2005
2
OUTLINE
  • Lidar Systems in Space
  • Lite
  • Glas
  • Calypso
  • 2. Validation of Space-borne Lidar Systems
  • Lite
  • Glas
  • Calypso

3
LITE
4
LITE
LITE Laser In Space Technology Experiment On
space shuttle flight STS-64, Sept. 9 to 20, 1994
  • Instrument Characteristics
  • NdYAG laser operating at 1064 nm, 532 nm, and
    355 nm.
  • Laser firing rate 10 Hz.
  • Column profile measurements separation 740 m.
  • Vertical sampling resolution 15 m.
  • Atmospheric sampling column diameter 275 m to
    450
  • Receiving telescope diameter 0.95 m.

5
The LITE Instrument
6
Coverage of Orbit 34
7
Voltage received at LITE at 532 nm during orbit
34, September 12, 1994 latitudes 14.79 to 9.21,
longitudes 29.26 to 32.65. Image from
http//www-lite.larc.nasa.gov/n_the_images.html.
8
GLAS
GLAS Geoscience Laser Altimeter System GLAS is
the laser system on ICESat. ICESat is a satellite
system intended to measure ice altitudes, but it
also yields information of atmospheric interest.
9
GLAS INSTRUMENT PARAMETERS
Indide in the solder combined chemically with
the gold electrodes and the first GLAS laser quit
working about a month after launch. The duty
cycle is presently only two or three days a
month. The operational temperature has also been
reduced.
10
GLAS DATA PRODUCTS
  • 532 and 1064 normalized lidar signal
  • Calibrated, attenuated backscatter cross section
    profiles for 532 and 1064 at 40 Hz and 5 Hz
  • Top and bottom of Planetary Boundary Layer
  • Top and bottom of elevated aerosol layers
  • Cloud layer top and bottom height
  • 532 attenuation corrected backscatter and
    extinction profiles
  • Thin cloud and aerosol layer optical depth

11
SAMPLE GLAS DATA PRODUCT
An example of the 532 nm data is shown for
October 6. The track starts in the central
Pacific, crosses Antarctica, proceeds over Africa
and Europe and then covers northern Greenland and
Alaska.(Spinhirne et al. , Aersosol and Cloud
observations and data products by the Glas Polar
Orbiting Lidar Instrument)
12
Other examples from Glas
Ref Spinhirne et al, 2004
13
GLAS PSC Observations
GLAS 532 nm backscatter ratio shows Polar
Stratospheric Clouds over Antarctica, Sep 29 2003
14
GLAS PSC Observations
15
(No Transcript)
16
CALIPSO
Calipso is a satellite system consisting of
three instruments a lidar (Caliop), an imaging
infrared radiometer and a wide field camera. The
Calipso satellite will fly in formation in the A
Train that is, the Aqua satellite constellation
consisting of the Aqua, CloudSat, Calipso,
Parasol and Aura satellite missions.
17
The Calipso Instrument Suite
18
CALIOP PROPERTIES
Two diode pumped NdYAG lasers emitting linearly
polarized light at 1064 and 532 nm. Beam
diameter 70 m at surface Three-channel receiver
for backscatter at 1064 and two polarized
components at 532 nm Sampling resolution is 30 m
vertical 333 m horizontal Will obtain backscatter
data from surface to 40 km
Winker and Pelon, 2003
19
CALIPSO Data Products
20
Expected Calypso Coverage
21
Validation of Space Lidar Systems
  • Validation of
  • LITE
  • GLAS
  • CALYPSO (Proposed)

22
DIFFICULTIES
  • Alignment of airborne measurements relative to
    spacecraft
  • Lack of homogeneity in viewing scene
  • Different contributions to multiple scattering
  • Assumptions on lidar ratio

23
The Lidar Ratio (Sa)
The lidar equation tells us that the normalized
lidar signal is given by where and where
The Rayleigh backscatter and extinction can be
evaluated theoretically. If we know the Lidar
aerosol ratio, we can determine
the aerosol backscatter and extinction.
24
Model (MIE) Calculated Sa
Nominal Model 532 nm Sa
Values Aerosol Type Sa Marine 20 Dust
20 Continental Clean
40 Polluted 80 Smoke 50
Reagan, Thome, Powell, 2001
25
Measured Values of Sa
Aerosol Classifications and Sa Ranges, 550
nm Classification Sa Range Sea
Salt 20 to 30 Clean Upper Free
Troposphere 20 to 30 Dust Elevated
Saharan 30 to 40 General, Near Ground 20
to 30 Smoke, Elevated Biomass Burning 45 to
60 Continental General (somewhat clean) 30 to
50 Urban Polluted 50 to 80
Reagan, Thome, Powell, 2001
26
LITE VALIDATION
During the LITE experiment validations were
carried out with over fifty ground based lidars.
Other correlative validation experiments were
also carried out. We briefly describe two such
validations (chosen randomly) those of Gu et al.
and of Cuomo et al.
27
Validation by Gu et al.
  • Lidar at Arecibo, Puerto Rico
  • Rayleigh Lidar at Starfire, New Mexico
  • Balloonsondes launched at local midnight from
    both sites
  • Backscatter ratios differ by less than 5
  • RMS Temperature differences as low as 2 K.
  • Used Sa of 30 in troposphere and 50 in
    stratosphere

28
Comparison with Arecibo Lidar
Gu et al., Appl. Optics, 1997
29
Temperature Comparison (Uncorrected Lidar Temp)
Gu et al., Appl. Optics, 1997
30
Temperature Comparison (Corrected LITE
Temperature)
Temperature corrected for aerosol backscatter
Gu et al., Appl. Optics, 1997
31
Validation of Cuomo et al.
  • Lidar systems at Potenza and Napoli
  • Operated /- 2 hours of overpass
  • H2O and N2 also measured
  • 14 radiosondes for temperature, RH, density
  • Used different values of Sa

32
Values of Sa of 35 and 20 agree equally well with
LITE data
Sa 35
Sa 20
33
GLAS VALIDATION
Of the many GLAS validations, we consider only
the validations carried out with the NASA Cloud
Physics Lidar (CPL) that is mounted on the ER-2
high altitude aircraft. This simulates a
space-borne lidar. Results taken from McGill et
al, 2004 and Hlavka et al., 2004.
34
CPL Properties
  • CPL, a quasi-spaceborne instrument, operates on
    the ER-2 giving a unique high altitude downward
    looking lidar that is an excellent validation and
    simulation tool for space borne lidar
    instruments.
  • CPL is similar to both the GLAS and CALIPSO
    lidars
  • CPL uses NdYVO4 at 1064, 532 and 355 nm
  • GLAS validation seven underflights to within
    tens of meters of the sub-satellite track.
  • Multiple scattering not important for CPL but
    cannot be neglected for GLAS (due to wider field
    of view)

Ref McGill et al, 2004
35
Validations
  • Intercomparison of GLAS and CPL profiles.
  • 1-second of GLAS profiles (7 km) are compared to
    35 seconds (7km) of CPL profiles
  • GLAS is much noisier outside the thin cirrus
    layer, but matches almost perfectly in the cloud.
  • The stronger GLAS signal below the cloud shows
    evidence of multiple scattering causing laser
    light leakage through the cloud.
  • Both lidars are calibrated well with the Rayleigh
    scattering signal above the cloud

36
GLAS/CPL comparison. Green lineoverpass time
McGill et al, 2004
37
GLAS/CPL Comparison 17/10/03
Hlavka et al, 2004
38
Quantitative Comparison
Hlavka et al, 2004
39
Features ComparisonLayer Identification and
Discrimination for GLAS compared with CPL shows
that GLAS correctly identifies layers. CPL
discriminates beween aerosol types better due to
lower SNR
Hlavka et al, 2004
40
CPL and CRS act as proxies for CALIPSO and
CloudSat
BLUE cloud/aerosol layers observed only by
lidar YELLOW cloud/aerosol layers observed only
by radar GREEN cloud/aerosol layers observed
only by both lidar and radar (CRS Cloud Radar
System on ER-2)
McGill et al, 2004
41
CALIPSO VALIDATION
  • Success Criteria
  • Comparisons of products and uncertainties with
    validated independent data products of high
    quality.
  • The user community is given sufficient
    information to understand the quality of the data
    in terms of precision and relative accuracy.

42
Validation Plan
  • Validation Includes
  • Instrument performance (SNR, linearity)
  • Algorithms
  • Quantification of random and bias errors
  • Quantification of assumptions in algorithms
  • Comparison of data products with similar products
    from independent, well validated instruments
  • Comparison with other satellite data sets

43
Pre-Launch Activities
Calibration and Characterization of Instrument
Performance Algorithm Evaluation Correlative
Instrument Development and Characterization
Ref CALIPSO Science Validation Plan Winker,
Trepte, Pelon, Garnier, Tom Kovacs
44
AerosolValidation
Verification of lidar footprint geolocation and
altitude registration Assessment of pointing
biases Evaluation of on-orbit calibration Lidar
profile calibration Aerosol layer height and
thickness Bacscatter profile, extinction profile,
optical depth. Estimate of Sa. Estiimate of
mulitple scattering parameter h
45
Cloud Product Validation
Problems include short lifetimes and short
correlation spatial scales, so plan is to acquire
airborne measurements of a few critical
parameters that can be compared with Calipso
observations. Cloud height and thickness Cloud
extinction profile and optical depth Profile
measurements of Sa and h Cloud phase and ice
water content Cirrus cloud emmisivity and
particle size
46
Correlative Data Sources
Field Campaigns Dedicated aircraft
measurements INTEX, AVE, TCSP, TC4, TWP-ICE,
SAMUM, MIRAGE, AMMA
47
CPL USED TO VALIDATE THE CALIPSO FEATURE FINDING
ALGORITHM Top CPL 532 nm backscatter Feb 19,
2003 Center Synthetic Calipso data derived from
CPS measurements Bottom Layer boundaries
determined by the Calipso feature finding
algorithm
48
CONCLUSION
Space borne lidar systems will generate a great
deal of valuable data on the characteristics of
the atmosphere, but to be useful, these data must
be validated with ground based and airborne
instruments.
49
The End
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