image ratios and indices - gis.unbc.cagis.unbc.ca/wp-content/uploads/2013/05/indices2017.pdf ·...
TRANSCRIPT
Image ratios and indices
Ratios… are used to enhance albedo contrasts by reducing inter-band similarities
e.g. Near-IR / Red … to identify vegetation
e.g. Red / Mid-IR … to identify snow / ice
Ratio Vegetation Index (RVI) = Near IR / Red …… if < 1 = unvegetated
Difference Vegetation Index (DVI) = NIR - Red ……if < 0 = unvegetated
* DVI is influenced by different lighting
Combining these two creates the most common ‘normalized’ vegetation index:
Normalised Difference Vegetation Index: NDVI
Normalised Difference Vegetation Index NDVI
Division compensates for differential illumination
It gives a close estimate of biomass
This yields values between -1 and +1 … requiring a 32 bit (‘real’) channel
Negative values of NDVI (values approaching -1) correspond to water.
Values close to zero (-0.1 to 0.1) = barren areas of rock, sand, or snow.
low, positive values represent shrub and grassland (approximately 0.2 to 0.4),
high values indicate temperate and tropical rainforests (values approaching 1)
Special sensors for NDVI
SPOT 5 has extra bands / wide sensor in visible/NIR with 1 km resolution to capture a repeat 2400 km swath for global coverage
MODIS (2000->)and NOAA-AVHRR (1979->) have specific red /near-IR bands for NDVI
NDVI is used measure vegetation amount or biomass, in regional and global estimates. "NDVI is directly related to photosynthesis and thus energy absorption of plant canopies"
Seasonal animation: https://archive.org/details/SVS-3584
NDVI global monitoring: https://glam1.gsfc.nasa.gov/
http://www.grayhawk-imaging.com/useofndviimagery.html
Delineation of Grizzly Bear Habitat in Bute InletGEOG432 project
Sieved maximum NDVI result
The use of NDVI to determine vegetative green-up after a forest fire Geog432
1987 2002
NDVI NDVI
The use of NDVI to determine vegetative green-up after a forest fire
NDVI difference – 1987-2002
Red - Negative Growth Range Clear - Neutral Growth Range
Yellow - Minimal Positive Growth Orange - Maximum Positive Growth
http://abstracts.rangelandmethods.org/doku.php/remote_sensing_methods:normalized_burn_ratio
Similar indices: Normalised Burn Ratio (Index)(Near IR – Mid-IR) / (Near IR + Mid-IR) Landsat TM: NBR = (4-7)/(4+ 7)
Other indices include (among many):
Soil-adjusted Vegetation Index (SAVI) = 1.5 * (NIR - R) / (NIR + R + 0.5)
Optimised Soil-adjusted Vegetation Index (OSAVI) = (NIR - R) / (NIR + R + 0.16)
-----------------------------------------------------------------------------
Green: NDGI= (NIR-G) / (NIR+G) TM = (4-2)/ (4+2)
Snow: NDSI = (Green-MIR) / (Green+MIR) TM = (2-5) / (2+5)
Water: NDWI = (NIR – MIR)/ (NIR + MIR) TM = (4-5) / (4+5)
Tasseled Cap transformation ArcMap 10.3
The Tasseled Cap (Kauth-Thomas) transformation is designed to analyze and
map vegetation and urban development changes detected by satellite sensors.
It is known as the Tasseled Cap transformation due to the data graphical shape.
It was developed in 1976 by R.J. Kauth and G.S. Thomas of the Environmental
Research Institute of Michigan (ERIM). The researchers found the patterns in
Landsat MSS data of agricultural fields as a function of the life cycle of the crop.
Essentially, as crops grow from seed to maturity, there is a net increase in near-
infrared and decrease in red reflectance based on soil color
e.g. Brightness = .433*C1 + .632*C2 + .586*C3 + .264*C4 (for each pixel)
The technique was named after the pattern of spectral change of agricultural crops during senescence, plotting brightness against greenness. The sequence is:
1. Bare fields / newly planted crops - high brightness, low greenness (spring)
2. Plant Growth - <-<- brightness (early summer)
3. Maturity: -> -> greenness (late summer)
4. Senescence (harvest) - bare field/stubble: <-<-greenness, ->-> brightness (Fall)
Tasseled Cap Transformation
MSS data, the 4-band dataset creates channels:
Brightness, Greenness, Yellowness (non-such)
TM data, 6-band (no thermal)
Brightness
Greenness
Wetness
Tasseled Cap Transformation
Kauth, R. J. and Thomas, G. S., 1976, The tasseled cap --a graphic description of the spectral-temporal development of agricultural crops as seen in Landsat, in Proceedings on the U.S. Department of the Interior 9 U.S. Geological Survey
Symposium on Machine Processing of Remotely Sensed Data, West Lafayette, Indiana, June 29 -- July 1, 1976, 41-51.
Landsat 5 TM coefficients for the Tasseled Cap
Band Brightness Greenness Wetness1 .3037 -.2848 .15092 .2793 -.2435 .19733 .4743 -.5436 .32794 .5585 .7243 .34065 .5082 .0840 -.71127 .1863 -.1800 -.4572
Character: Overall reflectance NIR v Visible MIR v NVIR
Coastal
Band 1
Blue
Band 2
Green
Band 3
Red
Band 4
NIR
Band 5
SWIR1
Band 6
SWIR2
Band 7
Brightness 0 0.3029 0.2786 0.4733 0.5599 0.5080 0.1872
Greenness 0 -0.2941 -0.2430 -0.5424 0.7276 0.0713 -0.1608
Wetness 0 0.1511 0.1973 0.3283 0.3407 -0.7117 -0.4559
Landsat 8 OLI coefficients
Why are they different at all ?
Brightness – measure of soil reflectance
Greenness – vegetation
Wetness – soil and canopy moisture
tasseled cap channels: 6 TM bands reduced to 3 meaningful channels
NDVI v Tasseled Cap greennessboth contrast the NIR versus visible reflectance
TCA Greenness is similar to NDVI, with subtle differences and is used in habitat studies.
Figure :John Paczkowski MSc thesis – remote sensing and grizzly bear habitat
–but only developed for some sensors…(the coefficients vary according to spectral wavelengths and radiometric resolution)
PCI Geomatica
Landsat 1-3 MSS
Landsat 5 TM
Landsat 7 ETM+
- NOT Landsat 8 OLI
Other ?:CBERS-02B (China/Brazil)
Ikonos, Quickbird 2
ASTER / MODISRussian tassel cap
Reasons to use Tassel Cap Analysis
It reduces a multi band dataset (4-6) to 3 channels –Brightness, Greenness, Wetness – each might be useful
The 3 channels could be used in classification / thresholds
The coefficients are universal for each sensor
Also known as the Tasseled Toque in Canada (fake news .. RS humour]
http://www.sjsu.edu/faculty/watkins/tassel.htm
Intro to Env. Change assignment
Select two images to highlight change during 1984-2017
Use landsatLook images - MIR/NIR/Red composites
Landsat 5: 1984-2011; L7: 1999-2003; L8: 2013-17
Download and process in next week lab period
http://remotepixel.ca
https://landsat.usgs.gov/landsat-8
https://earthexplorer.usgs.gov/
https://glovis.usgs.gov/
https://landsatlook.usgs.gov/