1. Measuring Vegetation Characteristics
Going beyond land cover

2. Vegetation characteristics
Some commonly measured characteristics:
Vegetation structure
Phenology
Primary productivity
Leaf area index
Vegetation health/vigor
Research is ongoing to improve existing indices and create new ones and to tie these assorted indices to useful environmental/ecological processes
Some indices are created in a production environment on a global scale and others are created on a case-by-case bases
Measurement of these indices is based on the fact the reflectance, transmittance, and scattering of energy in a canopy is greatly affected by vegetation structure and how vegetation components (leaves, branches, trunk) interact with the wavelength(s) of energy used by a particular instrument

3. Vegetation indices
Uses the fundamental principle that chlorophyll in green healthy vegetation largely absorbs red and blue wavelengths of light and strongly reflects near-infrared wavelengths
Closely related to primary productivity
Dozens of vegetation indices have been developed
Often composited for periods ranging form 8 days to one month
Often used to monitor changes in productivity over time

4. Band 3 (Red)
Band 4 (near-IR)
RGB image
NDVI

5. Popular vegetation indices
Normalized Difference Vegetation Index (NDVI)
NDVI = (NIR – Red) / (NIR + Red)
Most common vegetation index
Value is always between +1 and -1 with green vegetation closer to +1 and no vegetation close to 0
Negative values are possible for non-vegetated features
Somewhat sensitive to radiometric contaminants

6. Popular vegetation indices
Enhanced Vegetation Index (EVI)
Developed to improve upon NDVI
Output as a standard MODIS product
EVI = G*[(NIR-Red)/NIR+C1*Red-C2*Blue+L)] where G, C1, C2, and L are coefficients:
G = Gain factor (2.5 for MODIS)
L = Canopy background adjustment (1 for MODIS)
C2 = Atmospheric aerosol resistance (6 for MODIS)
C2 = Atmospheric aerosol resistance (7.5 for MODIS)
These coefficients reduces atmospheric effects in the red band and compensates for the different ways in which near-IR and red light behaves inside and below a canopy thereby reducing the effect of soil type, soil moisture, surface litter, and snow cover.
EVI is more sensitive to canopy structure than NDVI

7. Continuous fields data
Each pixel provides a proportional estimate of woody vegetation (needleleaf or broadleaf and evergreen or deciduous), herbaceous vegetation, and bare ground
A standard MODIS product available for the globe (except the poles) at a resolution of 500 meters
Initial reports are quite positive on the utility of this layer for species distribution models

8. Use of active sensors to measure vegetation characteristics
Radar and lidar are used to measure vegetation structure characteristics such as:
Height
Density
Timber volume
Canopy volume
Biomass
This is an area of active research and additional indices will certainly be developed and more sophisticated instruments will be developed during the next several years