Sensor technology

Question 1

What are the two sensor types?

Answer 1

Active
Passive

Question 2

What is an active sensor?

Answer 2

A sensor that provides their own energy source

Question 3

What are the 3 advantages of using an active sensor?

Answer 3

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

Question 4

What is an example of an active sensor?

Answer 4

LiDAR

Question 5

How does LiDAR work?

Answer 5

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)

Question 6

What is a passive sensor?

Answer 6

A sensor that measures energy that is naturally available- either reflected from surface or reemitted energy from surface at a different wavelength

Question 7

What are the limitations of passive sensors?

Answer 7

They require sunlight/emission from ground
-so they can only collect in day
Cant see through clouds

Question 8

What is a platform?

Answer 8

A remote sensing platform carries the sensor

Question 9

What are the types of platform?

Answer 9

Ground based
Airborne
Spaceborne

Question 10

What are the two factors that determine where the platform is located for the appropriate target?

Answer 10

The spatial resolution- what detail is required
The area coverage- how big is the area

Question 11

What is the most common type of platform used for environmental remote sensing?

Answer 11

Spacebourne

Question 12

What are the 4 benefits of spacebourne remote sensing?

Answer 12

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

Question 13

How does a geostationary satellite work?

Answer 13

Orbits the earth- with the earths rotation-view the same point
Works at a high altitude- 36,000km

Question 14

What are the 3 benefits of a geostationary satellite?

Answer 14

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

Question 15

How does a polar orbiting satellite work?

Answer 15

Orbits around the earth while earth spins within/below it
Low altitude- 800km

Question 16

What is the temporal resolution of a polar orbiting satellite?

Answer 16

1-16 days to collect data from the same region

Question 17

What is a benefit of a polar orbitting satellite?

Answer 17

Global coverage

Question 18

What are the four resolutions of remote sensing?

Answer 18

Spatial resolution
Spectral resolution
Radiometric resolution
Temporal resolution

Question 19

What is spatial resolution?

Answer 19

The smallest size of an object that can be picked out from its surrounding objects or features
Higher = 1m or 0.1m

Question 20

What is spectral resolution?

Answer 20

The width and number of wavebands that the sensor is able to measure

Question 21

What are the benefits of Landsat?

Answer 21

Data collected has been very similar in terms of wavebands
Easy to compare old and new data
Most satellites collect data in atmospheric windows

Question 22

What is radiometric resolution?

Answer 22

Number of values that can be stored