Sensor technology Flashcards
What are the two sensor types?
Active
Passive
What is an active sensor?
A sensor that provides their own energy source
What are the 3 advantages of using an active sensor?
They can:
Obtain measurements anytime- not reliant on sun
Examine wavelengths that are not sufficiently provided by the sun (e.g. microwaves)
Can see through clouds, depending on the wavelength
What is an example of an active sensor?
LiDAR
How does LiDAR work?
It transmits a pulse of energy
Records time taken from emission to absorption
Height value created
Derives information on vegetation canopies (height, biomass, forest structure)
What is a passive sensor?
A sensor that measures energy that is naturally available- either reflected from surface or reemitted energy from surface at a different wavelength
What are the limitations of passive sensors?
They require sunlight/emission from ground
-so they can only collect in day
Cant see through clouds
What is a platform?
A remote sensing platform carries the sensor
What are the types of platform?
Ground based
Airborne
Spaceborne
What are the two factors that determine where the platform is located for the appropriate target?
The spatial resolution- what detail is required
The area coverage- how big is the area
What is the most common type of platform used for environmental remote sensing?
Spacebourne
What are the 4 benefits of spacebourne remote sensing?
Cheaper- expensive to build and launch but they last and collect data for longer
Long operation- >5 years
Repetitive orbits- consistent long term observation of same location
Global coverage- certain models e.g. climate change need global data
How does a geostationary satellite work?
Orbits the earth- with the earths rotation-view the same point
Works at a high altitude- 36,000km
What are the 3 benefits of a geostationary satellite?
Used by meteorological and communication satellites
Provides the same view of the earth every 15-30 minutes
Can be used to monitor the weather over entire hemispheres of the earth
How does a polar orbiting satellite work?
Orbits around the earth while earth spins within/below it
Low altitude- 800km
What is the temporal resolution of a polar orbiting satellite?
1-16 days to collect data from the same region
What is a benefit of a polar orbitting satellite?
Global coverage
What are the four resolutions of remote sensing?
Spatial resolution
Spectral resolution
Radiometric resolution
Temporal resolution
What is spatial resolution?
The smallest size of an object that can be picked out from its surrounding objects or features
Higher = 1m or 0.1m
What is spectral resolution?
The width and number of wavebands that the sensor is able to measure
What are the benefits of Landsat?
Data collected has been very similar in terms of wavebands
Easy to compare old and new data
Most satellites collect data in atmospheric windows
What is radiometric resolution?
Number of values that can be stored
