1 Vegetation Indices Prof. Arnon Karnieli The Remote Sensing Laboratory Jacob Blaustein Institute...
-
Upload
sandra-kelly -
Category
Documents
-
view
215 -
download
3
Transcript of 1 Vegetation Indices Prof. Arnon Karnieli The Remote Sensing Laboratory Jacob Blaustein Institute...
1
Vegetation IndicesVegetation Indices
Prof. Arnon Karnieli
The Remote Sensing LaboratoryJacob Blaustein Institute for Desert Research
Ben-Gurion University of the NegevSede-Boker Campus 84990, ISRAEL
Prof. Arnon Karnieli
The Remote Sensing LaboratoryJacob Blaustein Institute for Desert Research
Ben-Gurion University of the NegevSede-Boker Campus 84990, ISRAEL
2
DefinitionDefinition
3
SR = NIR/Red
Simple Ratio (SR)Simple Ratio (SR)
4
Vegetation healthVegetation health
5
• The SR is based on the difference between the maximum absorption of radiation in the red (due to the chlorophyll pigments) and the maximum reflection of radiation in the NIR (due to the leaf cellular structure), and the fact that soil spectra, lacking these mechanisms, typically do not show such a dramatic spectral difference.
• The values of the SR range from 0 to infinity
• SR uses radiance, surface reflectance (), or apparent reflectance (measured at the top of the atmosphere) rather than digital numbers.
Characteristics of SRCharacteristics of SR
6
NIR-Red scatterplotNIR-Red scatterplot
SR = NIR/RedNIR
7
DNs for Band A: 62 54 39 43
The same ground cover has different DNs...
DNs for Band B: 71 63 24 31
Spectral Ratioing may alleviate the problem...
ExampleExample
8
DNs for Band A: 62 49 19 27 Band B: 71 63 24 31 Ratio A/B: 0.87 0.78 0.79 0.87
The same groundcovers now havesimilar DNs...
Example (Cont.)Example (Cont.)
9
NDVI = (NIR- Red)/(NIR+ Red)
The Normilized Difference Vegetation IndexThe Normilized Difference Vegetation Index
10
• NDVI has the advantage of varying between -1 and +1, while the SR ranges from 0 to infinity.
• In NDVI it is easier to separate snow, clouds, and water (negative values) from soil and vegetation (positive values).
1
1
SRNDVI
SR
SR vs. NDVISR vs. NDVI
11
SR vs. NDVISR vs. NDVI
12
High index values dense/health vegetation
Low index values sparse/stress vegetation
Typical NDVI values:Bare soils: 0.08 – 0.1Desert vegetation: 0.1 – 0.3Tropical forest: 0.4 – 0.6Water, snow, clouds: <0
Interpretation of NDVIInterpretation of NDVI
13
High Correlation with: • Photosynthetic activity• Vegetation cover• Leaf area index• Green leaf biomass• Carbon fluxes• Foliar loss and damage• Chlorophyll contentAlso used for:• Crop classification• Plant Phenology• Change detection
Applications of NDVIApplications of NDVI
14
Leaf Area Index is defined as the total one- side green leaf area per unit ground surface area (m2/ m2).
Leaf Area Index (LAI)Leaf Area Index (LAI)
LAI example
LAI = 6 means 6m2 leaf area per 1m2 ground area.
15
It is an important biological parameter because: It defines the area that interacts with solar radiation and provides the remote sensing signal It is the surface that is responsible for carbon absorption and exchange with the atmosphere..
Leaf Area Index (LAI)Leaf Area Index (LAI)
Destructive sampling
Radiation measurements
Remote sensing
MethodsDirect: Indirect:
16
Non-linear correlationsNon-linear correlations
17
Linear correlationsLinear correlations
18
NDVI calculationsNDVI calculations
19
Red
Near
Infr
are
d
NDVINDVI
NDVI productNDVI product
NIR - R
NIR + R
20
NDVI derived from NOAA-AVHRR
NDVI - IsraelNDVI - Israel
21
True Color NDVI
NDVI of snowNDVI of snow
22
Low NDVI VALUEHighLow NDVI VALUEHigh
NDVI PhenologyNDVI Phenology
23
VI optimizationVI optimization
24
August Average NDVI, AfricaAugust Average NDVI, Africa
25
Maximum Value Composite (MVC)Maximum Value Composite (MVC)
2,400 km
26
Day 10.120.200.100.15
Day 20.150.100.500.12
Day 30.090.500.150.11
***************
Day n0.060.250.630.11
Composite0.150.500.630.15
Pixel 1 Pixel 2 Pixel 3 Pixel 4T
ime
Maximum Value Composite (MVC)Maximum Value Composite (MVC)
27
MVC - importanceMVC - importance
• Eliminate effects of cloud cover
• Eliminate effects of atmospheric
aerosols
• Eliminate effects of view zenith angle
• Eliminate effects of solar zenith angle
Forward view angle
Backward view angle
Nadir
2330 km SWATH
28
residual clouds
Maximum Value Composite (MVC)Maximum Value Composite (MVC)
29
NDVI time seriesNDVI time series
Movie
30
NDVI global coverageNDVI global coverage
Movie
31
Soil and Vegetation Reflectance ScatterplotSoil and Vegetation Reflectance Scatterplot
Red
NIR
32
Perpendicular Vegetation Index (PVI)Perpendicular Vegetation Index (PVI)
A
B
C
D
E
Red Reflectance
NIR
Ref
lect
ance
Soil Back
ground L
ine
Greening Line
A, B = Pixels of bare soilC, D = Pixels of partly green vegetation cover.E = Pixel of green vegetation
21 a
baPVI
RNIR
The objective of PVI is to remove the effect of soil brightness and isolate reflectance changes due to vegetation only
33
NDVI – soil sensitivityNDVI – soil sensitivity
34
(1 )NIR R
NIR R
SAVI LL
L = 1 For low vegetation densityL = 0.5 For intermediate vegetation density;L = 0.25 For high vegetation density.
Soil Adjusted Vegetation Index (SAVI)Soil Adjusted Vegetation Index (SAVI)
35
SAVISAVI
36
NDVI – soil sensitivity SAVI – soil sensitivity
Soil sensitivitySoil sensitivity
37
Surface colorSurface color
38
( )
NIR rb
NIR rb
rb red blue red
ARVI
The resistance of the ARVI to atmospheric effects (in comparison to the NDVI) is accomplished by a self-correction process for the atmospheric effect on the red channel, using the difference in the radiance between the blue and the red channels to correct the radiance in the red channel.
= 1.0
Atmospheric Resistant Vegetation Index Atmospheric Resistant Vegetation Index
39
NNormalized DDifference
VVegetation IIndex
NIR RED
NIR RED
NDVI
AAtmospheric RResistant
VVegetation IIndex
NIR rb
NIR rb
ARVI
rb RED BLUE RED
Atmospheric
Resistance
SSoil AAdjusted
VVegetation IIndex
NIR RED
NIR RED
SAVI LL
1
Soil Background Correction
EEnhanced VVegetation
IIndex
NIR RED
NIR RED BLUE
EVI GL c c1 2
The ultimate index!
Enhanced Vegetation Index (EVI)Enhanced Vegetation Index (EVI)
40
The enhanced vegetation index (EVI) was developed to optimize the vegetation signal with improved sensitivity in high biomass regions and improved vegetation monitoring while correcting for canopy background signals reducing atmosphere influences.
1 2
NIR R
NIR R B
EVI GC C L
where are atmospherically-corrected or partially atmosphere corrected (Rayleigh and ozone absorption) surface reflectances, L is the canopy background adjustment term, and C1, C2 are the coefficients of the aerosol resistance term, which uses the blue band to correct for aerosol influences in the red band. The coefficients adopted in the EVI algorithm are, L=1, C1 = 6, C2 = 7.5, and G (gain factor) = 2.5.
Enhanced Vegetation Index (EVI)Enhanced Vegetation Index (EVI)
41
EVI Image of Riparian, Wetland, and Agricultural Areas along the Lower Colorado River and U.S.-Mexico Border
Enhanced Vegetation Index (EVI)Enhanced Vegetation Index (EVI)
42
Ndvi vs. EVINdvi vs. EVI
43
EVI – global coverageEVI – global coverage
44
Red Edge
Blue Shift of the Red edgeBlue Shift of the Red edge
Blue Shift
45
Red Edge PositionRed Edge Position
0
10
20
30
40
50
60
600 650 700 750 800 850 900
Wavelength (nm)
Ref
lect
ance
(%
)
RREP
REP
670 780 700 740 700700 40(((( ) / 2) ) /( ))rep
B7
B10
B9
B8
46
Red edge positionRed edge position
47
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
700 710 720 730 740 750 760 770 780 790 800
Wavelength (nm)
Ref
lect
ance
0.000
0.005
0.010
0.015
0.020
0.025
700 710 720 730 740 750 760 770 780 790 800
Wavelength (nm)
1s
t D
eri
va
tiv
e
Reflectance
2nd Derivative
1st Derivative
-0.0010
-0.0008
-0.0006
-0.0004
-0.0002
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
700 710 720 730 740 750 760 770 780 790 800
Wavelength (nm)
2n
d D
eri
va
tiv
e
Red edge positionRed edge position
48
False color image
2nd derivative image
Red edge positionRed edge position
49
Perpendicular Vegetation Index:
Vegetation Indices – summary (1)Vegetation Indices – summary (1)
21 a
baPVI
RNIR
/NIR RSR
NIR R
NIR R
NDVI
Simple Ratio:
Normalized Difference Vegetation Index:
50
(1 )NIR R
NIR R
SAVI LL
( )
NIR rb
NIR rb
rb red blue red
ARVI
1 2
NIR R
NIR R B
EVI GC C L
Vegetation Indices (2)Vegetation Indices (2)
Soil Adjusted Vegetation Index:
Atmospheric Resistance Vegetation Index:
Enhanced Vegetation Index:
51
Types of vegetation indicesTypes of vegetation indices
Ratio-based (red and NIR spectral bands):
SR, NDVI, ARVI
Orthogonal-based difference of red and NIR spectral bands:
PVI
Hybrid/combination of the two:
SAVI, EVI