Flashcards in Remote Sensing and GIS (Year 2) - Part 2 - Remote Sensing Deck (68)
Define Remote Sensing
Obtaining information about the Earth, without physical contact, but by measurement of electromagnetic radiation (e.g. visible light, infrared, ultraviolet, micro waves, or thermal energy)
What are the two types of remote sensing?
Passive and Active
What is passive remote sensing?
Measures radiation coming from a natural source -> e.g. sun or earth
What is active remote sensing?
Measures radiation coming from an artificial source -> generated by the sensor itself and measures what come back
What is radiation?
Transfer of heat and energy through empty space
All objects with a temperature above absolute 0 do what?
What is electromagnetic radiation?
Form of sinusoidal waves which propagate through space at the speed of light, by analogy with water waves
How are individual electromagnetic waves categorised?
Frequency v (how many waves pass per second) and wavelength (the distance between successive peaks)
Short wavelength of electromagnetic waves equals what frequency
What is the electromagnetic spectrum made up of?
A ‘family’ of EM waves, each has a characteristics wavelength and frequency
Hotter bodies generate more of what type of radiation?
Colder bodies generate more of what type of radiation?
What is the atmospheric window/window regions?
Windows where energy radiation passes through the atmosphere (most EMR passes through)
What happens to EMR as it passes through the atmosphere?
Scattering and absorption
What are the three interactions that occur EMR reaches the earth's surface?
- reflected: when a ray of light strikes a non-transparent surface and bounces back
- absorbed: the thermodynamically irreversible transformation of radiant energy into heat (this energy is later re-emitted from the surface)
- transmitted: when radiation passes through a substance without significant attenuation
What does the proportion reflected, absorbed and transmitted depend on?
• the nature of the surface – city vs jungle
• the wavelength of the EMR – wavelengths interact with different surfaces
• the angle of illumination – angle the energy is coming in at
Why is the wavelength (λ) dependency of interactions of EMR with the earth's surfaces critically important?
• An important concept for Earth observation is that different surfaces have a different “spectral signature”
• Surfaces have different responses due to different interactions with portions of the EMR spectrum (i.e. specific ‘lights’, or rather, specific wavelengths)
• City heat maps -> based on wavelength -> how do cities vary?
• Can tell different spaces apart based on their spectral signature -> response to light (their wavelength)
What are the two types of remote sensing range configurations?
Ground based and airborne systems
What is the ground based configuration for remote sensing?
E.g., measuring reflection of natural surfaces. In situ measurements are widely used to calibrate and atmospherically-correct airborne or satellite-derived data being acquired at the same time -> Cranes and towers enable measurements to be taken over larger surface areas than handheld instruments
What is the airborne systems configuration for remote sensing?
Are used to collect data from a higher vantage point. Fixed-wing aircraft are the platform of choice for most applications, as they provide a stable, flexible platform for small-area, high resolution survey, and testing of sensors before they go into space. More recently = drones
What is the most common remote sensing configuration?
Satellite based RS
What is the main purpose of remote sensing?
RS is helping us understand Earth as a system at largest scales
(not cameras) – detecting instrument
sensor is attached to a platform (satellites themselves)
What is the relationship between sensors and platforms?
Sensors are the detecting instruments that are mounted on platforms (i.e. the satellites, or spacecraft)
Define spatial resolution in relation to remote sensing
pixel size on ground (km/m)
Define temporal resolution in relation to remote sensing
repeat pass (e.g. daily repeat)
Define spectral resolution in relation to remote sensing
number/width of bands of EMR identified
Define spatial coverage in relation to remote sensing
area of earth imaged (km)