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Advanced Optical theoryModelling and Data
ProcessingJose Moreno
3 September 2007, Lecture D1La4
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 2
ADVANCED OPTICAL THEORYPart I: Signal modelling and data pre-processing
Signal modelling at the satellite level
Radiometric corrections: calibration and noise removal
Atmospheric correction
Topographic normalisation
BRDF corrections
Working with data series: spatial and spectral consistency
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 3
Signal Modellingat the Satellite Level
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 4
•The atmosphere modifies theradiation measured by opticalsensors:• Aerosols and gases presentoptical activity at VIS/NIR/SWIR.• Reflectance increases / decreases depending on thewavelength.• Image loses contrast.
Removing the atmospheric influence from remote sensing data is necessary before data exploitation
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 5
MULTIPLE CONTRIBUTIONS TO THE SIGNAL
6S formulation
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 6
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 7
Planck’s Law
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 8
0
10
20
30
40
50
60
70
0 2000 4000 6000 8000 10000 12000 14000
Wavelength (nm)
Sola
r Rad
ianc
e (µ
W/c
m2 /n
m/s
r)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0AtmosphereSolar 1.0 ReflectanceEarth 300 K, 1.0 Emisivity
Earth Radiance (µW
/cm2/nm
/sr)Available Signal
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 9
800
1000
1200
1400
1600
1800
2000
2200
0.4 0.5 0.6 0.7 0.8 0.9 1
6S
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 10
0100200300400500600700800900
10001100120013001400150016001700180019002000210022002300240025002600
0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
wavelength ( m)
Sola
r Irr
adia
nce
(W m
m
)-1
-2μ
μ
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 11
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 12
Thuillier model (2003)Based on solar spectral irradiance measurements from:
(a) SOLar SPECtrum (SOLSPEC) spectrometerflew with the ATmospheric Laboratory for Applicationsand Science (ATLAS) missions
(b) SOlar SPectrum (SOSP) spectrometerflew on the EUropean Retrieval CArrier (EURECA) missions
and data from Upper Atmosphere Research Satellite (UARS)
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 13
800
1000
1200
1400
1600
1800
2000
2200
400 500 600 700 800 900 1000
TUILLIER 2003
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 14
0.0
0.5
1.0
1.5
2.0
2.5
0
500
1000
1500
2000
2500
400 500 600 700 800 900 1000
SMARTS_ChKur
SMARTS_newKur
SMARTS_Gueymard
SMARTS_oldKur
SMARTS_ThKur
SMARTS_Wehrli_WRC85
SMARTS_CebChKur
mW/m2/nmm
W/m
2/nm
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 15
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
0.60 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.70 0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78 0.79 0.80
wavelength ( m)
Sola
r Irr
adia
nce
(W m
m
)-1
-2μ
μ
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 16
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 17
ABSOLUTE SOLAR IRRADIANCE CHANGES
δL δT δRL
= 4 + 2T R
Temperature variations
Radius variations
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 18
COUPLING OF AEROSOLS AND WATER VAPOUR VERTICAL STRUCTURE
Vertical aerosol amount andtype variability:- continental bottom layer- maritime upper layer
+ diurnal boundary layerevolution
aerosols vertical structure water vapour vertical structure
High spatial and temporalvariability:- atmospheric circulation- topography
+ turbulent structure
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 19
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 20
spectral scattering albedorural aerosol model
(for 0, 70, 80 and 99% humidity)
spectral scattering albedomaritime aerosol model
(for 0, 70, 80 and 99% humidity)
SPECTRAL VARIABILITY IN AEROSOLS EFFECTS
coupled to angular variability (different phase functions)
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 21
Aerosol type phase functionλ = 550 nm
ANGULAR VARIABILITY IN AEROSOLS EFFECTS
coupled to vertical structure
aerosols can change the shape ofthe TOA-observed surface BRDF
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 22
MODELING OF ADJACENCY EFFECTS IN THE DEFINITION OF SPATIALLY AVERAGED 'ENVIRONMENT' REFLECTANCES
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 23
Dealing withatmosphericadjacency effectsin an accurate wayrequires quitecomplicatednumericalcomputations !!!
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 24
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 25
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 26
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 27
Effective atmospheric Point Spread Function (PSF)
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 28
Radiometric corrections:calibration andnoise removal
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 29
Pre-processing steps:- Radiometric calibration
- Noise removal
- Cloud screening
- Geometric correction
- Atmospheric correction
- Database management
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 30
• Pre-launch radiometric calibration to traceable standard (accepted reference)
• Post launch calibration campaigns to maintain/monitoring in flight calibration (vicarious)
• On-board calibration (both radiometric and spectral)
RADIOMETRIC CALIBRATION
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 31
Pre-launch calibrations
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 32
AVHRRs’ sensors’ response over time
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 33
Univ. Valencia
M. Cutter
Radiometric calibrationProba/CHRIS data
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 34
ORIGINAL IMAGE CORRECTED IMAGE
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 35
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 36
NOISE REMOVAL: Example for CHRIS data
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 37
Spectralradiometriccalibration
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 38
Atmospheric correction
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 39
Measured Top-Of-Atmosphere signal
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 40
• TOA radiance modeled assuming Lambertian reflectance for the target:
• Analytically invertible to retrieve ρs.
• Removal of adjacency effects
Surface reflectance retrieval
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 41
Non-Lambertian areas with topographic structure:- no analytic inversion under approximations- decoupling 'effective' reflectances and 'effective‘ geometric termsrequired for environment
- multistep numerical procedure required for inversion- multiple reflection terms only significant for high reflectance surroundings
Flat Lambertian areas:
INVERSION OF SURFACE REFLECTANCE
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 42
• Cloud screening based on static thresholds over TOA reflectance and spectral slope.
• 2 sets of thresholds:– “Restrictive” set: detects pixels with minimum probability of
clouds AOT retrieval– “Relaxed” set: detects pixels with a high probability of
clouds CWV and reflectance retrieval
Cloud masking
Relaxed Restrictive
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 43
CLOUD SCREENING
- Very dependent on the availablespectral information
- Many different algorithms (from simplethresholds up to sophisticate techniques)
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 44
• Retrieval of AOT for each cell• Filling-in empty cells.• Conversion from VIS to AOT at
550nm
AOT retrieval
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 45
Very largevariability in aerosolscontent
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 46
14 July 2003
14 July 2004 17 July 2004
SPARC Campaigns, Barrax (Spain)
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 47
Surface reflectance retrievalAtmospheric correction: Removal of the atmospheric effectsfrom the measured at-sensor radiance, leading to thederivation of surface reflectance images.
AerosolsWater vapor
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 48
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 49
Topographic normalisation
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 50
Effects introduced by topography:A - Vertical geometric distorsion (horizontal displacement due to relief)
B - Variation of atmospheric (optical) properties with height
C - Relative changes in slope and orientation of surface introduce variations in illuminationconditions:
Direct irradiance:- illuminated areas- self-shadowed areas- cast-shadowed areas
Diffuse irradiance:- directional distribution- modeling of sky view factors
Surface reflectance model:- non-Lambertian effects- modeling of direct/diffuse components
D - Adjacency effects (additional contributions)
E - Additional multiple reflections
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 51
µs DEM
µil
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 52
DEM L0 Edir·µs Edif
Cosine correction
Hay’s model
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 53
TOTAL APPARENT REFLECTANCE
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 54
SIMPLE SEMI-EMPIRICAL FORMULATIONS OF SURFACEBIDIRECTIONAL REFLECTANCE MODELS USED FOR
ATMOSPHERIC/TOPOGRAPHIC NORMALIZATION
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 55
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 56
Other simple empirical models:
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 57
BRDF corrections
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 58
nine types of reflectance measurements
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 59
OUTPUT OF THEATMOSPHERIC/TOPOGRAPHICCORRECTION FOR QUANTITATIVECOMPARISONS IN MULTITEMPORALSTUDIES
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 60
BRDF normalization with aclass specific Ambrals model(U. Beisl, 2001)
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 61
PROSPECT+SAIL simulation Actual CHRIS/PROBA data
Alfalfa field
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 62
Bach et al., 2006
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 63
Hot spot effect
POLDER HyMAP
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 64
Working with data series:spatial and spectral
consistency
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 65
corn
wheat
Temporalevolution of
surface reflectance
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 66
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 67
2003 growingSeasonBarrax
Validation 15/07/2003 LANDSAT LAI
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0
LANDSAT retrieved
Gro
und
mea
sure
men
ts ALFALFACORNPAPAVERPOTATOSUGARBEETGARLICONION
CORNALFALFA
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 68
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 69
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 70
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 71
SPATIAL CONSISTENCY
- Spatial resolution of individual images in the series
- Geocoding accuracy- Resampling methods
- Changes in view angle implychanges in geometry (resolution)
- Composites of multiple satellite dataare especially critical
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 72
Temporalseriesmade with a combinationof images frommultiple satellitesmust take care ofdifferent spectralsampling
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 73
“similar”spectralbandsare notalwaysfullycompatible
3 September 2007 D1La4 Advanced Optical – Modelling and Data Processing Jose Moreno 74
MODELLING ASPECTS- bare soil bi-directional reflectance modelling - leaf reflectance/transmittance modelling - canopy bi-directional reflectance modelling - atmospheric effects in surface reflectance (diffuse radiation) - at sensor radiance modelling (surface+atmosphere)
model inversion techniques classification techniques
- energy/water surface-atmosphere exchange processes - role of vegetation dynamics in the terrestrial carbon cycle
data assimilation techniques spectral unmixing