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)

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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/