week 9

Question 1

direct sampling vs remote sensing

Answer 1

• direct sampling includes all activities where in situ measurement or samples are collected at close range
• remote sampling entails sampling or measuring from distance

Question 2

operational definition

Answer 2

remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance, typically from satellite or aircraft

Question 3

technical definition

Answer 3

remote sensing is the science of acquiring, processing and interpreting images that record the interaction between electromagnetic energy and matter

Question 4

pros and cons of ground based measurements

Answer 4

pros:
- high temporal resolution
- seismicity measureable
- not impacted by weather
cons:
- low spatial extent
- can be destroyed in eruptions
- expensive
- high technical skillset required

Question 5

pros and cons of satellite based measurements

Answer 5

pros:
- high spatial extent and resolution
- many key datasets free and opensource
- processed data available online
cons:
- typically only daily temporal resolution
- highly impacted by weather (clouds)
- technical skillset required for advanced processing

Question 6

what is solar irradiance

Answer 6

the measurement of the sun’s energy for a given area at one moment in time

Question 7

what is solar insolation

Answer 7

the measurement of the sun’s energy for over a specific time period

Question 8

what is radiance

Answer 8

the energy emitted by an object

Question 9

what is the stefan boltzmann law

Answer 9

as the kinetic temperature of an object increases, its radiance also increases
E = sigmaT^4

Question 10

what is a black-body

Answer 10

a hypothetical object that absorbs all incoming radiation, thus heating itself and then radiates the energy with a temp defined spectrum and perfect emissivity

Question 11

what is wien’s displacement law

Answer 11

as temp increases, the radiance at all wavelengths also increases but the peak emission shifts to shorter wavelengths
lambdapeak = b/T

Question 12

what are reflectance curves

Answer 12

• the proportion of incoming radiation reflected vs absorbed

Question 13

absorption in the atmosphere

Answer 13

• EM travelling through the atmosphere is partly absorbed by various molecules. the most efficient of these are ozone, water and CO2
• due to absorption, much of the EM spectrum is not useable for remote sensing

Question 14

describe transmission in the atmosphere

Answer 14

-transmissivity is the measure of to what degree the atmosphere allows EM radiation to pass through it
- we can adjust for transmissivity to calculate before it passed through atmosphere

Question 15

when does scattering occur

Answer 15

when the particles of gaseous molecules cause EM waves to be redirected

Question 16

what is rayleigh scattering

Answer 16

• occurs when the particles are smaller than the wavelength
• responsible for blue skies and sunsets

Question 17

what is mie scattering

Answer 17

• occurs when particles are similar size to the incoming radiation

Question 18

what is non-selective scattering

Answer 18

• when particle size is much larger than the incoming wavelength
• all wavelengths are scattered equally and is the reason clouds appear white

Question 19

what is a pixel

Answer 19

• an ‘average’ received radiation from all sources falling within the boundaries of the pixel
• low resolution is a limitation of all remotely sensed data

Question 20

how are land cover maps created

Answer 20

by assessing the reflectance curve of a pixel

Question 21

what are supervised maps

Answer 21

use training data allowing for detailed classifications, typically used in smaller targeted areas

Question 22

what are unsupervised maps

Answer 22

group pixels with similar reflectance curves. able to quickly create broad destinations globally

Question 23

what are remote sensing indices

Answer 23

• allow amalgamation of multiple data bands into simpler data sets
• generally find the difference between two bands

Question 24

what is the normalised difference vegetation index

Answer 24

NDVI = NIR - red/ NIR + red

Question 25

Detecting Thermal Anomalies

Answer 25

To distinguish volcanic thermal anomalies from very reflective surfaces the Normalised Thermal Index (NTI) is calculated NTI > -0.8

Question 26

Volcanic Radiative Power (VRP)

Answer 26

𝑽𝑹𝑷 𝝓𝒆 = 𝟏. 𝟖𝟗 × 𝑨𝑷𝑰𝑿 × 𝑫𝑷𝑰𝑿 𝑨𝑷𝑰𝑿 is the area of the pixel, and 𝑫𝑷𝑰𝑿 is the abovebackground MIR radiance of the pixel * VRP is the total heat radiated across the area of the anomaly at the time of acquisition – typically expressed as Watts or Mega Watts

Question 27

Uses for VRP

Answer 27

* VRP is useful as a monitoring parameter for increasing unrest especially at closed-vent systems * At open-vent systems it can be used to estimate the height of lava lakes/ exposed magma columns (proxy for pressure) * Can be used to estimate Time Average Discharge Rates of lava flows (effusion rates) which can be fed into real-time lava flow modelling

Question 28

Digital Elevation Models (DEMs)

Answer 28

* DEMs are remote sensing data sets that represent “bare earth surface” elevation. * DEMs differ from DSMs which include the surface of objects such as trees and buildings * DSMs are typically made using LiDAR and DEMs can be derived from DSMs. * Large scale DEMs are made using altimetry but the pixel resolution is much larger (relatively) resulting in terrain rather than surfaces are measured

Question 29

uses of altimetry

Answer 29

- make large scale DEMs - measure sea level - measure sea ice thickness

Question 30

Detecting deformation with InSAR

Answer 30

Low earth orbit satellites “illuminate” the Earth with their own radar source * Radar penetrates most weather clouds and is equally effective at night * Requires at least 2 satellite overpasses of an area from similar viewpoints * The phase difference ∆𝜙 of a radar wave targeting the same location describes the change in surface elevation

Question 31

Interferograms

Answer 31

* InSAR is capable of detecting changes on the scale of millimetres to 10s of centimetres * Interferograms use coloured “fringes” to describe ground movement * The closer together the fringes are the greater the rate of deformation * These can be used to locate faults responsible for earthquakes or where deformation is focused at volcanoes