Practice questions

Question 1

Name and describe the THREE types of atmospheric
scattering that can occur when radiation passes through the
atmosphere

Answer 1

Rayleigh Scattering
Size of the atmospheric particles should be smaller
that wavelength of radiation
Mie scattering
Size of the atmospheric particles should be equal
that wavelength of radiation
Non-selective scattering
Particles much larger than incident radiation (e.g. water
droplets and large dust particles)

Question 2

Explain the term wavelength and provide 2 of its units

Answer 2

Wavelength  (distance between wave crests)
Units : Micrometers (µm), nanometers (nm)

Question 3

Name the four major components of a remote sensing system.

Answer 3

1) Source (Sun or Active sensor)
2) Atmosphere
3) Earth Surface
4) Sensor

Question 4

Name and describe the 4 types of resolution

Answer 4

• Spatial - the size of the field-of-view, e.g. 10  10 m.
• Spectral - the number and size of spectral regions (or frequencies) the sensor records data in, e.g. blue, green, red, near-infrared, thermal infrared.
• Temporal - how often the sensor acquires data, e.g., every 30 days.
• Radiometric - sensitivity of detectors to small
  differences in electromagnetic energy.

Question 5

Which TWO processes can occur to radiation as it passes
through the atmosphere?

Answer 5

Scattering and absorption

Question 6

What 3 processes can occur when incident radiation
interacts with an object and which of these is measured
by a remote sensing instrument in the optical wavelength
range?

Answer 6

Electromagnetic radiation can be
either
1) reflected - measured by the sensor
2) absorbed
3) transmitted

Question 7

Draw a typical spectral reflectance curve for vegetation.
What are the main factors that affect the spectral reflectance
of vegetation ?

Answer 7

Y axis - Reflectance 0 - 80%
x axis - wavelength 0.4 - 2.6
visible between 0.4-0.7 = blue green red
lowest reflectance for blue up to 20% for green and back to 10 for red.
NIR between 0.7 and 1.3 - up to 40% for cell structure.
SWIR between 1.3 and 2.6 trough at 1.4, 2 and 2.6 for water absorbtion and peaks at 1,7 (30% and 2.2 for 10%

Question 8

If this is NIR waveband where are the water pixels located in
the histogram?

Answer 8

Draw a typical spectral reflectance curve for vegetation.
What are the main factors that affect the spectral reflectance
of vegetation ?

Question 9

Name THREE types of reflectance from water

Answer 9

Surface reflectance
* Volume reflectance
* Bottom reflectance

Question 10

Define the equation for the normalised difference vegetation
index (NDVI), indicating what its input parameters are? Name
TWO cover types that would have negative NDVI values.

Answer 10

 NIR − red
 NIR + red
Snow, water, clouds