1. UNIT 2 – MODULE 5: Multispectral, Thermal & Hyperspectral Sensing

2. MULTISPECTRAL SENSING

3. MULTISPECTRAL SCANNERS*
Instruments that are designed to collect data in more spectral bands over a wider range of the EM spectrum.
Can also sense in very narrow bands.
Acquired through two primary methods: across-track scanning & along-track scanning.
Credit: NASA
Remote Sensing: What is Multispectral Mapping? (3:08):
Credit: National Air & Space Museum

4. ACROSS-TRACK SCANNING
These systems build 2-D images of the terrain beneath an aircraft.
Uses a rotating or oscillating mirror, these scanning mirror systems scan back-and-forth along the flight line at right angles.
Once incoming energy is reflected off the scanning mirror system, it is separated into several spectral components that are sensed independently.
Credit: NASA
Credit: Fundamentals of Remote Sensing - Schiewe, 2006

5. ALONG-TRACK SCANNING
Records multispectral image data beneath an aircraft, just like across-track scanners.
Difference: linear array of detectors are used in replace of a rotating or oscillating mirror.
Each spectral band of sensing requires its own linear array.
Credit: NASA
Credit: Fundamentals of Remote Sensing - Schiewe, 2006

6. MIRROR SCANNING VS LINEAR ARRAY
Linear array systems have several advantages:
Acquire Stronger Signals
Smaller, Weigh Less, Use Less Energy
Higher Reliability (No Moving Parts)
Longer Life Expectancy
Disadvantages: the need to calibrate significantly more detectors, and limited range of spectral sensitivity.

7. ACROSS-TRACK MULTISPECTRAL SCANNER
Credit: Remote Sensing & Image Interpretation - Lillesand, Kiefer, Chipman

8. ACROSS-TRACK IMAGERY Blue Green Red near IR near IR thermal IR
Credit: Remote Sensing & Image Interpretation - Lillesand, Kiefer, Chipman

9. ALONG-TRACK MULTISPECTRAL SCANNER
Credit:

10. ALONG-TRACK IMAGERY Credit: Leica Geosystems
Credit: EarthData International

11. THERMAL SENSING

12. THERMAL SCANNING *
Multispectral scanning that is limited to the thermal portion of the EM spectrum.
Provide for very rapid results.
To maximize sensitivity, detectors need to be kept artificially cooled (i.e. liquid nitrogen) to near absolute zero.
Credit: NOAA
Aerial Thermal Imaging with a Drone (1:08):
Credit:

13. THERMAL RADIATION PRINCIPLES
Radiant vs. Kinetic Temperature
Blackbody Radiation
Radiation from Materials
Atmospheric Effects
Thermal Radiation Interaction w/Terrain
Credit: USGS

14. RADIANT VS KINETIC TEMPERATURE
Radiant Temperature – energy being emitted off of matter.
Kinetic Temperature – energy of moving particles in matter.
Internal temperature of an object may not match external readings.
Credit: National Park Service

15. RADIANT VS KINETIC EXAMPLE
A body of water as a whole will have a cooler temperature than the surface temperature that’s recorded by a thermal sensor.
Credit: Dr. Roy Spencer
Credit: Remote Sensing & Image Interpretation - Lillesand, Kiefer, Chipman

16. BLACKBODY RADIATION Objects that absorb all radiation.
Nothing is reflected.
Can emit their own light if hot enough.
The Sun and other stars are blackbodies.
Real materials do not behave like blackbodies.
Credit: glossary.periodni.com

17. RADIATION FROM MATERIALS
Real materials only emit only a fraction of energy that a blackbody would.
Emitting ability of a material is called emissivity.
Emissivity describes how efficiently an object radiates energy. Based on a scale of zero (low) to one (high).
Can vary with wavelength, viewing angle, soil conditions, etc.

18. TYPICAL EMISSIVITIES OF COMMON MATERIALS
Credit: Remote Sensing & Image Interpretation - Lillesand, Kiefer, Chipman

19. THERMAL RADIATION: INTERACTION W/ TERRAIN
The lower an object’s reflectance, the higher the emissivity, and vice-versa.
Example: water has little-to-no reflectance in the thermal part of the spectrum.
Its emissivity is nearly 1.
Credit: Department of Energy

20. ATMOSPHERIC EFFECTS
Has a major impact on intensity & spectral composition of energy acquired by a thermal system.
Atmospheric windows influence the selection of spectral bands for measuring thermal energy.
Credit: Penn State University

21. INTERPRETING THERMAL SCANNER IMAGERY
For many thermal scanning operations, simply studying relative differences in radiant temperatures will suffice.
The time of day is of great importance when analyzing thermal scanner imagery.
Materials warm up and cool down, throughout the day & night, at different rates.
Credit:

22. THERMAL SCANNERS: RADIOMETRIC CALIBRATION
Modern thermal scanners have internal blackbody source referencing, which enables for more accurate readings.
Air-to-ground correlation accounts for atmospheric effects by correlating scanner data with actual surface measurements.
Credit: USGS

23. F.L.I.R. SYSTEMS Forward Looking Infrared Radar*
Forward Looking Infrared Radar
Instead of acquiring views directly beneath an aircraft, FLIR systems can acquire ahead of an aircraft.
Civilian applications: search & rescue, pollution, fire fighting, nighttime driving, etc.
FLIR Landing at Colorado Airport (1:59):
Police Track Suspects with FLIR Technology (2:48):
Credit: Massachusetts State Police

24. HYPERSPECTRAL SENSING

25. HYPERSPECTRAL SENSING*
Difference between multispectral & hyperspectral sensing is:
Number of Bands
Narrowness of the Bands
Multispectral data: bands of large bandwidths ( nm).
Hyperspectral data: bands of narrow bandwidths (5-10 nm).
Credit: NASA
Hyperspectral Imaging (2:11):
Credit:

26. HYPERSPECTRAL SENSING (Continued)*
Hyperspectral sensing combines imaging & spectroscopy into a single system.
Allow us to see the unseen more than a multispectral system.
Limitations: water vapor can have a significant impact on data collection.
Credit: HyVista Corporation
Automated Sorting of Almonds Using Hyperspectral Technology (0:52):
Have students read the following:
Credit: Headwall Photonics