Lecture 5 - Sensor Technology Flashcards
Two Sensor types
Active Sensors
Passive Sensors
Active Sensor advantages
Can obtain measurements anytime of day
Examine wavelengths not sufficiently provided by sun e.g microwaves
Can see through clouds in certain wavelengths
What do active sensors do?
Provide their own energy source for illumination
How do LiDAR sensors work?
Transmit pulse of energy (red, green or NIR) to the surface using the time between pulse being emitted and pulse being received.
What are LiDAR sensors for?
Mapping surface height
Deriving information on vegetation canopies
What do passive sensors do?
Measure energy that is naturally available.
Limitations for passive sensors
Require sunlight/emission from ground objects
Can only collect data in the day and can’t see through clouds
Advantages of passive sensors
Cheaper to maintain and launch
Limitations of active sensors
Expensive to maintain and launch
Considerations needed when taking data
How much detail do you need?
How big is the area you’re covering?
Advantages of spaceborne remote sensing
- Cheaper
- Long operation <5 years
- Repetitive Orbits
- Global coverage
Geostationary Satellites
High altitude - 36,000km
Moving above equator in synchro with Earth
Use of Geostationary satellites
Used by meteorological and communications satellites
Advantages of Geostationary satellites
Provides the same view of the Earth every 15-30 minutes
Can monitor weather over entire hemisphere of the Earth.
Polar Orbiting satellite
Low altitude - 800km
Revisit time of Polar Orbiting satellite
Varies from twice daily to every 16 days to observe the same region
Uses of Polar Orbiting Satellites
Environmental remote sensing and full global coverage
Four resolutions of Remote sensing
Spatial Resolution
Spectral resolution
Radiometric resolution
Temporal resolution
Spatial Resolution
The smallest size of an object that can be picked out from its surroundings or features
Expressed in units of km, meters, cm
Spectral resolution
Number and dimension of the specific wavelength interval of the EMR that a sensor is capable of measuring
How many spectral wavebands may a satellite have?
4-30 wavebands
Panchromatic Spectral resolution
Consist of one wide band that encompasses a large spectral range
Multispectral waveband
Consists of narrower, several bands of which two or three band in the VR and also a few bands in NIR and MIR bands
Hyperspectral resolution
Consists of large number of narrower bands across EMR
Benefits of Landsat
Data collected through its life has been very similar in terms of wavebands so its consistent.
What wavebands does Sentinel 2 cover?
Blue to shortwave IR wavebands
Temporal resolution
Shortest period of time that a sensor will revisit / pass over the same spot on the Earth’s surface.
Why are some regions imaged more frequently?
Overlap in imaging swaths for satellites
