DN to Reflectancehonda/textbooks/advrs/DN2Reflectance_2p.pdf2 Definition of NDVI:Reflectance at...
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Transcript of DN to Reflectancehonda/textbooks/advrs/DN2Reflectance_2p.pdf2 Definition of NDVI:Reflectance at...
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DN to Reflectance
HONDA Kiyoshi
Contents
Definition of NDVIRadianceReflectanceHow to Calculate Radiance from DNIrradiance
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Definition of NDVI
Red Visibleat eReflectanc:InfraredNear at eReflectanc:
NDVI
VR
NIR
VRNIR
VRNIR
ρρ
ρρρρ
+−
=
Reflectance
Ratio of Radiant Energy Reflected to Incident EnergyRadiant Energy = Integral of vertical components of Radiance Measured ( by satellite to be scaled back from DN )
anglezenith Solar :),cos(/ IrradianceSolar Spectral:
/ Irradiance Spectral :
/ Surface theof Radiance Spectral :
eReflectanc Spectral :
2
2
2
sss
s
ss
mmWEmmWG
msrmWL
EL
GL
θθµµ
µ
µ
ρµππρ
λ
λ
λ
λ
λ
λ
λλ
=⋅
⋅
⋅⋅
==E
θ
πL
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DN ?
DN ( Digital Number ) you can see in the RS image files is not Reflectance.So you have to derive Reflectance from the DNThen what is DN ?
DN is a scaled Radiance DN is scaled from Radiance measured by sensors
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter6/chapter6.html
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Radiance
Energy in unit time, unit solid angle, unit wavelenth
msrmWmsrmsJ µµ ⋅⋅=⋅⋅⋅ 22 // :unit
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter6/chapter6.html
Z
dω
dA
dλ
λωλ ddtdAdEnergyL received=
DN to Radiance (Lλ)
Have to find out LMAX, LMIN, QCALMAX, QCALMIN
biasoffsetQCALDN
LMINQCALMINQCALMAXLMINLMAXoffset
QCALMINQCALMAXLMINLMAXgain
LMINQCALMINQCALQCALMINQCALMAXLMINLMAXL
oroffsetDNgainL
==
+−−
−=
−−
=
+−−−
=
+×=
,
)(
λλλ
λλ
λλλ
λ
λ
QCALMAX
QCALMIN
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LMIN, LMAX of LANDSAT7
LMIN, LMAX List
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.html
LMAX
LMIN
LANDSAT 7 Gain Setting for January
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter6/htmls/january_gains.html
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How to Find the Constants for Scaling factor of Radiance
Metadata file .metSample ftp://cgceopush3.geo.msu.edu/push3_2/137/043/p137r43_7x000228/p137r043_7x20000228.met
Identify Hi-Gain or Low GainEROS Data Center Gateway
• http://edcimswww.cr.usgs.gov/pub/imswelcome/
Obtain Hi-Gain and Low-Gain parametersUSGS LANDSAT Page
• http://landsat7.usgs.gov/technical_details/calibration_files/
Header file/recordData Handling Manuals
Processed in Japan, China, Thailand ….
How to obtain TOA Irradiance Spectral Exo-atmospheric Irradiance
anglezenith Solar :),cos(units alastronomicin distanceSun -Earth:
/ Irradiance SpectralSolor catmospheri-Exo Average:
/ Irradiance SpectralSolar catmospheri-Exo:2
2
2
sss
s
s
ss
ss
dmmWESUN
mmWEd
ESUNE
EL
GL
θθµ
µ
µ
µππρ
λ
λ
λλ
λ
λ
λ
λλ
=
⋅
⋅
=
==
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.html
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Average Solar Spectral Irradiance ESUNλ
Average Solor Spectral Exo-atmospheric Irradiance
mmWESUNmmWE
dESUNE
EL
GL
s
ss
ss
µ
µ
µππρ
λ
λ
λλ
λ
λ
λ
λλ
⋅
⋅
=
==
2
2
2
/ Irradiance Spectral catmospheri-Exo Average:
/ Irradiance SpectralSolar icstomospher-Exo:
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.htmlhttp://modarch.gsfc.nasa.gov/MODIS/ATM/solar.html
ESUNλ for ETM+
Sun Earth Distance ds
units alastronomicin distanceSun -Earth:
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s
ss
d
ESUNd
E λλ =
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.html
Relative Solar Irradiance 1/(ds*ds)
0.90
0.95
1.00
1.05
1.10
0 30 60 90 120 150 180 210 240 270 300 330 360
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Solar Zenith Angle
LANDSAT: Use Zenith Angle ( 90deg – Sun Elevation) at the centre of the image for the whole image
180km -> +- 0.81 degIf Zenith Angle < 20deg, difference < 1%
Or
Calculate the angle from Lat, Lon, Julian day and time ( i.e POSSOL of 6S ).
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.html
Atmospheric Correction
The reflectance we have obtained here is Apparent Reflectance or Reflectance at TOAAtmospheric correction is needed to obtain Reflectance at Ground LevelYou may run 6S with appropriate parametersSome products are Reflectance at Ground Surface, such as MODIS, SPOT VEGETAION…
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ReferencesLandsat 7 Science Data Users Handbook
Chapter6• http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter6/chapter6.html
Chapter 11• http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.html
Dr. Kawamura's page DN->Refelctance for Landsat ( Japanese )
http://www.geocities.jp/kensuke_kawamura/Others/LandsatCalibration/LandsatCalibration.html
6S Manual
