Spectral Indices

Question 1

What are spectral indices/profiles?

Answer 1

Combination of spectral reflectance from 2 or more wavelengths to indicate features of interest

Question 2

What are the ways energy interacts on earth surface features?

Answer 2

Can be reflected, absorbed, or transmitted.

Question 3

What does incident mean and can EMR do such?

Answer 3

Falling or striking something (object)
Yes

Question 4

Radiance is measured in…

Answer 4

Watts per steradian per square metre

(W * sr-1 * m-2)

Called the ‘Prinicple of Conservation of Energy’

Question 5

Reflectance equals…

Answer 5

Reflected radiation (captured by a sensor) / incident radiation (available) x 100%

SR of an object as a function of wavelength can be represented as a spectral reflectance curve

Question 6

The variation of energy is…

Answer 6

Wavelength dependent

Question 7

You distinguish features using…
Based on…

Answer 7

Spectral bands
Their reflectance

Question 8

Only design sensors to detect…

Answer 8

Energy in the spectral bands where EMR can pass through atmosphere freely.

Question 9

What are the three laws of EMR?

Answer 9

Stefan-Boltzmann Law
Plancks Law
Meins Displacement Law

Question 10

What is Stefan-Boltzmann Law referring?

Answer 10

The total emitted energy of a blackbody or total radiant exitance from the surface of a material

Higher temperature of radiator = greater total amount of radiation it emits

Question 11

What is a black body?

Answer 11

It is an ideal radiator because it absorbs 100% of the incident EMR and emits 100% of the heat.
INCREASED ENERGY = MORE EMITTED

Question 12

What is Planck’s Law referring?

Answer 12

The intensity of the emitted energy at a specific wavelength radiated at temperature T, function of wavelength

Shift to shorter wavelength in the peak of distribution curve as temperature increases

Question 13

What is Wien’s Displacement Law referring?

Answer 13

Identifies the peak emitted energy of a blackbody

Radiation curve reaches max spectral radiant exitance (various with absolute temperature)

Question 14

What is the dominant wavelength?

Answer 14

Radiation curve reaches its maximum label. This is where we see colour.

Question 15

What is radiometric correction?

How do we do it?

Answer 15

Improving accuracy and quality of data by removing or reducing effects of atmospheric, sensor and illumination noise

Convert a pixel’s digital number value to reflectance values

Atmospheric absorption and scattering of solar radiation at surface affects the true radiance at top of atmosphere, requiring correction to produce an at surface reflectance approximation

Question 16

What are the 5 other vegetation profiles (indices) instead of NDVI?

Answer 16

Enhanced Vegetation Index - minimises atmospheric scattering and canopy background noise
Soil Adjusted Vegetation Index - effect of soil background where vegetative cover is low
Vegetation Condition Index - comparing NDVI observation with range of values in the same period over years
Burn Area Index - indicate burned areas (brighter pixels = burnt)
Normalised Burn Ratio - indicate burned area (darker pixels = burnt)

NDVI describes vigor and health of green vegetation, falling between 0.20 and 0.80 values

Question 17

Why does NDVI produce inaccurate data?

Answer 17

Shadowing
Air moisture
Variations in sun incidence angle