Lecture 5 - Sensor Technology

Question 1

Two Sensor types

Answer 1

Active Sensors
Passive Sensors

Question 2

Active Sensor advantages

Answer 2

Can obtain measurements anytime of day
Examine wavelengths not sufficiently provided by sun e.g microwaves
Can see through clouds in certain wavelengths

Question 3

What do active sensors do?

Answer 3

Provide their own energy source for illumination

Question 4

How do LiDAR sensors work?

Answer 4

Transmit pulse of energy (red, green or NIR) to the surface using the time between pulse being emitted and pulse being received.

Question 5

What are LiDAR sensors for?

Answer 5

Mapping surface height
Deriving information on vegetation canopies

Question 6

What do passive sensors do?

Answer 6

Measure energy that is naturally available.

Question 7

Limitations for passive sensors

Answer 7

Require sunlight/emission from ground objects
Can only collect data in the day and can’t see through clouds

Question 8

Advantages of passive sensors

Answer 8

Cheaper to maintain and launch

Question 9

Limitations of active sensors

Answer 9

Expensive to maintain and launch

Question 10

Considerations needed when taking data

Answer 10

How much detail do you need?
How big is the area you’re covering?

Question 11

Advantages of spaceborne remote sensing

Answer 11

1. Cheaper
2. Long operation <5 years
3. Repetitive Orbits
4. Global coverage

Question 12

Geostationary Satellites

Answer 12

High altitude - 36,000km
Moving above equator in synchro with Earth

Question 13

Use of Geostationary satellites

Answer 13

Used by meteorological and communications satellites

Question 14

Advantages of Geostationary satellites

Answer 14

Provides the same view of the Earth every 15-30 minutes
Can monitor weather over entire hemisphere of the Earth.

Question 15

Polar Orbiting satellite

Answer 15

Low altitude - 800km

Question 16

Revisit time of Polar Orbiting satellite

Answer 16

Varies from twice daily to every 16 days to observe the same region

Question 17

Uses of Polar Orbiting Satellites

Answer 17

Environmental remote sensing and full global coverage

Question 18

Four resolutions of Remote sensing

Answer 18

Spatial Resolution
Spectral resolution
Radiometric resolution
Temporal resolution

Question 19

Spatial Resolution

Answer 19

The smallest size of an object that can be picked out from its surroundings or features
Expressed in units of km, meters, cm

Question 20

Spectral resolution

Answer 20

Number and dimension of the specific wavelength interval of the EMR that a sensor is capable of measuring

Question 21

How many spectral wavebands may a satellite have?

Answer 21

4-30 wavebands

Question 22

Panchromatic Spectral resolution

Answer 22

Consist of one wide band that encompasses a large spectral range

Question 23

Multispectral waveband

Answer 23

Consists of narrower, several bands of which two or three band in the VR and also a few bands in NIR and MIR bands

Question 24

Hyperspectral resolution

Answer 24

Consists of large number of narrower bands across EMR

Question 25

Benefits of Landsat

Answer 25

Data collected through its life has been very similar in terms of wavebands so its consistent.

Question 26

What wavebands does Sentinel 2 cover?

Answer 26

Blue to shortwave IR wavebands

Question 27

Temporal resolution

Answer 27

Shortest period of time that a sensor will revisit / pass over the same spot on the Earth's surface.

Question 28

Why are some regions imaged more frequently?

Answer 28

Overlap in imaging swaths for satellites