6.1 Indices Flashcards
Band composites
How to distinguish vegetation from soil
# How to distinguish vegetation from soil False-color B5/B4/B3 (NIR/Red/Green)
# How to distinguish water from the shadow Pseudocolor B8A/B7/B3
# How to distinguish cloud from snow Pseudocolor B11/B7/B3
What is Indice?
Quantitative measurements of different features –Vegetation –Water –Snow –Moisture –etc.
Advantages and Disadvantage of indices
Advantages:
–Simple to understand
–Easy to implement
–Fast (operation per scene instead of per pixel)
Disadvantage:
Empirical i.e. no physical meaning
Indice used for Band difference:
𝐷𝑉𝐼=𝑁𝐼𝑅−𝑅
Indice used for Band ratio:
𝑅𝑉𝐼=𝑁𝐼𝑅 / R
Indice used for Band normalized ratio:
NDVI = (NIR-R) / (NIR+R)
Difference Vegetation Index (DVI)
- Simplest vegetation index
- Distinguishes vegetation from soil
𝐷𝑉𝐼=𝑁𝐼𝑅−𝑅
–High values for vegetation
–Low values for soil
–Negative values for water
Difference Vegetation Index (DVI) disadvantages
×Large range of DVI –> difficult to compare (difficult to compare different area or images)
×Sensitive to atmosphere and shadow
Ratio Vegetation Index (RVI)
Simplest ratio based index to quantify vegetation greenness
𝑅𝑉𝐼=𝑁𝐼𝑅 / R
–Large RVI value: healthy vegetation
–Lower RVI values: water, soil, ice
Ratio Vegetation Index (RVI) disadvantages
×Impossible to calculate when R=0
×Large range of RVI –> difficult to compare
e.g. RVI = 0.5/0.08 = 6.25 -> healthy vegetation
RVI = 0.4 / 0.3 = 1.33 -> unhealthy vegetation
the image appears yellowish means lower vegetation density
Normalized Difference Vegetation Index (NDVI)
Quantify vegetation greenness
NDVI = (NIR-R) / (NIR+R)
–Ranging from -1 to 1
–Healthy vegetation: high NDVI values
–Clearwater: negative NDVI close to -1
–Sand , snow, cloud: low NDVI value close to 0
Normalized Difference Vegetation Index (NDVI) value and what it means
NDVI = (0.5-0.08) / (0.5+0.08) = 0.72 -> healthy vegetation NDVI = (0.4-0.3) / (0.4+0.3) = 0.14 -> unhealthy vegetation
NDVI >0.2 = sparse vegetation
NDVI >0.6 = dense vegetation
Normalized Difference Vegetation Index (NDVI) facts
- 16 km weekly NDVI
- Advanced Very High-Resolution Radiometer (AVHRR)
- 1 km spatial resolution, 4 6 spectral bands
- 2400 x 6400 spatial coverage
- Since 1979
Normalized Difference Vegetation Index (NDVI) disadvantages
•NDVI has a limited sense to high Leaf Area Index (LAI)
–LAI quantifies the amount of leaf materials in a canopy.
- Atmospheric condition alternates NDVI value
- NDVI is sensitive to background noise from soil
Enhanced Vegetation Index (EVI)
EVI quantifies vegetation greenness
(complicated equation)
–Corrects for some atmospheric condition and canopy background noise
–Ranging from -1 to 1
–Healthy vegetation between 0.2 and 0.8
–Effective for analyzing areas with large amounts of chlorophyll (e.g. rainforests