Post on 13-Jan-2016
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Stennis Space Center
Parameters Describing Earth Observing Remote Sensing Systems
Robert Ryan
Lockheed Martin Space Operations - Stennis Programs
John C. Stennis Space Center
December 2-4, 2003
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Stennis Space CenterContributors
NASA Stennis Space Center
Vicki Zanoni
Mary Pagnutti
NASA Goddard Space Flight Center
Brian Markham
Jim Storey
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Stennis Space CenterIntroduction
• Standard definitions for spatial, spectral, radiometric, and geometric properties are needed describing passive electro-optical systems and their products.
• Sensor parameters are bound by the fundamental performance of a system, while product parameters describe what is available to the end user.
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Stennis Space CenterIntroduction (Continued)
• Because detailed sensor performance information may not be readily available to an international science community, standardization of product parameters is of primary importance.
• User community desire as a few parameters as possible to describe the performance of a product or system.
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Stennis Space CenterIntroduction (Continued)
• Guidelines and standards are of little use without standardized terms.
• Studies that describe the impact of parameters on various applications are critically needed.
• This presentation is going to emphasize spatial.
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Stennis Space CenterSpecifying a Digital Imagery Product
•Spatial– Spatial/Frequency Domain– Aliasing
•Spectral (Sensor)– Panchromatic or Multispectral
•Radiometry– Relative– Absolute– Signal-to-Noise Ratio
•Geolocational Accuracy– Circular Error
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Stennis Space CenterSome Spatial Product Parameters
• Ground Sample Distance • Point Spread Function• Edge Response • Line Spread Function• Optical Transfer Function
– Modulation Transfer Function (MTF)
• Aliasing
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Stennis Space CenterGround Sample Distance
• Ground Sample Distance (GSD) is the distance between the center of pixels in an image– Products are typically resampled and do not
completely agree with intrinsic sensor sampling
• Most commonly used spatial parameter• Does not tell the whole story
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1.0 m GSD
0.2 m GSD 0.4 m GSD
0.6 m GSD
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Stennis Space CenterGSD 0.2 m GSD 0.2 m 2x2
GSD 0.2 m 3x3 GSD 0.2 m 4x4
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Point Spread Function
• Scene is considered to be a collection of point sources
• Each point source is blurred by the point spread function (PSF).
Displaced Point Spread Function
System
Point source Impulse Response (PSF)A
),( oo yyxxA
oS oAS
),( ,
,
oo yyxxAyxPSF
yxPSF
),( oo yyxxAPSF
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Stennis Space CenterImage Formation
• Image is convolution of point spread function (PSF) with input scene
objectinput theis y)(x,I
image theis y)(x,I where
),(),(),(
o
i
oooooi dydxyyxxPSFyxIyxI
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Stennis Space CenterOptical Transfer Function
• An equivalent measurement of the PSF is the Optical Transfer Function via a two dimensional Fourier Transform– Consists of Magnitude and Phase Terms
)),((),(),(),( jExpMTFyxPSFFTOTF
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Stennis Space CenterModulation Transfer Function
• MTF is a measure of an imaging system’s ability to recreate the spatial frequency content of scene
MTF is the magnitude of the Fourier Transform ofthe Point Spread Function / LineSpread Function.
1.0
Cut-off
Spatial frequency
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Stennis Space CenterSpatial/Frequency Domain
• Most specifications are written in terms of MTF as a function of spatial frequency– Dominant parameter is typically MTF @ Nyquist frequency– Nyquist frequency depends on GSD
• Nyquist frequency = 1/(2*GSD)
– MTF at Nyquist is a measure of aliasing
• Edge Response is more intuitive– RER (Relative Edge Response)– Ringing
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Edge Response and Line Spread Function
dx
d
)x(E
)x(l
x x
))0,(()0,()()0,(
)),((),(),(),(
jExpMTFxlFTOTF
jExpMTFyxPSFFTOTF
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Relative Edge Response
-2.5 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 2.5-0.2
0
0.2
0.4
0.6
0.8
1
1.2RingingOvershoot
RingingUndershoot
Region where mean slope is estimated
Ed
ge
Res
po
nse
Pixels
Edge slope is a simple description applicable for well behaved systems
Slope is approximately inversely proportional to width of PSF
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Aliasing
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Stennis Space CenterAssessing Levels of Aliasing
0
1
0
1
GSD/L= (GSD) (Slope) ~ 1 Moderately Aliased
GSD/L= (GSD) (Slope) << 1 No Aliasing
Nyquist Sampling: Need to sample at least twice the highest spatial frequency to reconstruct image
0
1GSD/L= (GSD) (Slope) > 1 Severely AliasedL
GSD
GSD
L
GSD
L
PSF
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Stennis Space CenterCIR Images of SRS Synthesized Products
AVIRIS 3.2 m GSD 16 m PSF, Slope 0.06 m-1
28.8 m PSF, Slope 0.035 m-1 35.2 m PSF, Slope 0.028 m-1 41.6 m PSF, Slope 0.024 m-1 48 m PSF, Slope 0.021 m-1
22.4 m PSF, Slope 0.045 m-19.6 m PSF, Slope 0.10 m-1
Savannah River Site - 28.8 GSD Simulations
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Landsat Spatial Resolution Trade Study
AVIRIS: ~3 m GSD, ~3 m PSFAfter ETM+ Band Synthesis
0.2
0.4
0.6
0.8
1.0
After 3x3 Boxcar Averaging:~10 m GSD, ~10 m PSF
After Additional 3x3 Filtering:~10 m GSD, ~30 m PSF
After Additional 3x3 Decimation:~30 m GSD, ~10 m PSF
After Additional 3x3 Averaging:~30 m GSD, ~30 m PSF
Actual Landsat 7 ETM+:30 m GSD, ~36 m PSF
NDVI
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Stennis Space CenterSpatial Parameter Summary
• Basic Description Well Behaved Systems– In track and cross track
• GSD, Edge Slope• GSD,PSF FWHM • GSD, MTF @ Nyquist
• Full Description– GSD and 2 D PSF or OTF
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Stennis Space CenterSpectral
• Basic Description– Center Wavelength– Full width half maximum– Slope edge at 50% points
• Others– Ripple
– Out-of-band rejection
• Full Description– Spectral response functions with units
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IKONOS Relative Spectral Response
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
350 450 550 650 750 850 950 1050
Wavelength (nm)
Rel
ativ
e S
pec
tral
Res
po
nsi
vity
Pan
Blue
Green
Red
NIR
Spectral Characteristics: Bands
System Spectral Response
•
•• •B
R
G
NIR
Band-to-Band Registration
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Stennis Space CenterRadiometry Specification
• Three Types– Linearity– Relative
• Pixel-to-Pixel• Band-to-Band• Temporal
– Absolute
• SNR
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Stennis Space CenterRadiometry: Linearity
Linear and non-linear response to input radiance
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Stennis Space CenterRadiometry: Relative
IKONOS Image of Antarctica – RGB, POID 52847
Normalized Average Row Values for Antarctica
Includes material © Space Imaging LLC
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Stennis Space CenterRadiometry: Absolute
0 200 400 600 800 1000 1200 1400 1600 1800 20000
5
10
15
20
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30NIR Band Calibration Summary
SSC, Big Spring, TX, 6/22/01SSC, Big Spring, TX, 8/5/01SSC, Lunar Lake, NV, 7/13/01SSC, Lunar Lake, NV, 7/16/01SSC, Maricopa, AZ, 7/26/01SSC, Stennis, 52 tarp, 1/15/02SSC, Stennis, 3.5 tarp, 1/15/02SSC, Stennis, 22 tarp, 1/15/02SSC, Stennis, Concrete, 1/15/02SSC, Stennis, Grass, 1/15/02SSC, Stennis, 52 tarp, 2/17/02SSC, Stennis, 3.5 tarp, 2/17/02SSC, Stennis, 22 tarp, 2/17/02SSC, Stennis, Concrete, 2/17/02SSC, Stennis, Grass, 2/17/02UofA/SDSU, Brookings, SD, 7/3/01UofA/SDSU, Brookings, SD, 7/17/01UofA/SDSU, Brookings, SD, 7/25/01UofA, Lunar Lake, NV, 7/13/01UofA, Lunar Lake, NV, 7/16/01UofA, Railroad Valley, NV, 7/13/01UofA, Railroad Valley, NV, 7/16/01UofA, Ivanpah, CA, 11/19/01SI Calibration Curve, Post 2/22/01
DN
Ra
dia
nc
e [
W/(
m2 s
r)]
SI Radiance = DN/84.3
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Stennis Space CenterSignal-to-Noise Ratio
• Several definitions exists• For well behaved systems (Very few bad
detectors) Basic Description– Temporal Noise or Shot Noise Limited– SNR for an extended uniform radiance scenes
• Advanced Description– Includes both detector nonuniformity, processing
and shot noise components
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Stennis Space CenterPan Band MTFC
Row MTFC slightly stronger
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
1
1.5
2
2.5
3
3.5
4
4.5
5Pan Kernel Column Section
Cycles/ Pixel-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Cycles/ Pixel
Pan Kernel Row Section
Pan Kernel
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Stennis Space CenterNoise Gain
SNR decreases with MTFC processing and the noise displays a spatial frequency dependence that did not exist at the
sensorBand Noise Gain
Blue 1.59
Green 1.63
Red 1.68
NIR 1.81
Pan 4.16
MTFC OFF SNR 25 MTFC ON SNR 13
NIR Kernel Applied to Simulated Imagery
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Stennis Space CenterSpatial Resolution: SNR
Original Maricopa IKONOS Imagery
SNR ~ 100
Maricopa IKONOS Imagery with Noise Added
SNR ~ 2
Includes material © Space Imaging LLC
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Stennis Space CenterGeolocation Accuracy
• Basic Description– RMSE– Circular Error (CE 90, CE 95)
• Full Description– Distribution Functions
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Stennis Space CenterCE90 Geolocational Accuracy
• A standard metric often used for horizontal accuracy in map or image products is circular error at the 90% confidence level (CE90). The National Map Accuracy Standard (NMAS) established this measure in the U.S. geospatial community. NMAS (U.S. Bureau of the Budget, 1947) set the criterion for mapping products that 90% of well-defined points tested must fall within a certain radial distance.
Includes material © Space Imaging LLC
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Data scatter plot showing the geolocational errors present in this imagery. Additionally, the CE90 (calculated by the FGDC standard method and by a percentile method) and the typical pixel size are shown on this plot.
Data scatter plot showing the geolocational errors present in this imagery. Additionally, the CE90 (calculated by the FGDC standard method and by a percentile method) and the typical pixel size are shown on this plot.
CE 90 Example
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Stennis Space CenterSummary
• For “well behaved” systems and products a few simple well chosen parameters can describe the system or product.
• Derived products can be significantly different than their intrinsic sensor data
• Studies that describe the impact of parameters on various applications are critically needed.