Lab - THERMAL IMAGERY

The purpose of Lab 10 is to familiarize you with interpreting thermal imagery. Upon completion of this lab you should be aware of the usefulness of thermal imagery in various applications.

Outline:

Materials (click to download)

Advanced Spaceborne Thermal Emission and Reflection Radiomter (ASTER): one of the sensors onboard the EOS satellites.
5 Thermal Infrared (TIR) bands covering the 8-12µm portion of the EMS. Spatial resolution 90m x 90m

LANDSAT TM Band 6 • spatial resolution – 120m x 120m (coarse relative resolution) • detects emitted energy (not reflected energy) • emitted radiation of earth’s surface reveals information concerning the thermal properties of materials • considered a ‘passive’ system in that it measures energy emitted from earth (as opposed to the sensor itself) • uncalibrated – relative temperatures (brightest tones generally indicate warmest surfaces) • provides qualitative information instead of quantitative • scanners generate geometric errors, therefore can’t be used for accurate measurements

Thermal Properties • Emissivity – ability to absorb & radiate heat; good absorbers = high emissivity • Conductivity – measure of the rate at which heat will flow through material • Capacity – ability of material to store heat • Diffusivity – measure of material’s internal heat transfer • Specific Heat/Thermal inertia – amount of energy necessary to raise 1 gram of substance 1 degree C (water has high specific heat)

Time of Day Considerations • Time of image acquisition is key information when interpreting thermal images • Time can be estimated by examining land/water comparisons • Typically: o greatest contrast between features on a day image o water cool on day images (dark) & warm on night images (bright) o vegetation relatively cool on day images (due to plant transpiration) o pavement/building materials appear bright; absorb a lot of heat & have a high thermal capacity

Time of Day Considerations • Differential heating & cooling • Predawn  Show residual heat remaining in objects at end of cooling period • Post-sunrise  Thermal shadows – cooler, darker areas on slopes away from sun • Temperature cross-over periods  Two periods (sunrise & sunset) when land/water have similar temps  Avoided for remote sensing

ThermalCurves.png Thermal Interpretation • Surface winds o Wind shadow – bright signature downwind from an obstruction to surface winds; caused by reduction of windchill in these areas o Wind streaks – alternating light/dark lines that are parallel to wind direction • Rain o Creates surface of cooler, more uniform temps • Clouds & Fog o Usually masks thermal IR emissions from surface o Results in darker tones o Cloud shadows: areas of surface that are in shadow of clouds; cooler, darker tones • Ghosts o thermal impressions of object that had been moved (dark)

Applications • Heat-loss analysis • Thermal pollution monitoring • Forest fire detection • Weather forecasting • Volcanic risk analysis ThermalExamples.png

Copy the Lab10 data to the local drive, and Open the ASTER images by using ERDAS 2014. Image 1 - Kansas City Open the image ast_l1b_00308302012041611_20120905142736_7327.img in ERDAS 2014. Locate each area using the inquire box . (Right click the image, you will find this tool in the list.) Change Units from Map to File. Location A Location B

Location C Location D

1.  Identify the features at the following locations: (4 points)
   

A. ________________________________

B. ________________________________

C. ________________________________

D. ________________________________

Open the ASTER daytime image in the same viewer (but don’t clear display) or in a separate view and link the two viewers.
2. How have these features changed between the day and night images? Explain your reasoning using any thermal capacity property (9 points) Day Night Reasoning B C D

3.  Using the night image and the file coordinates below, what feature do the white pixels represent? (1 point)
   

4. Look at the features of D in Question 1. Compare the day and night images. Explain the reason behind what you see using your knowledge of thermal infrared energy interactions and physical geography. (1 point)

5. What do bright features mean in the thermal images? Using your knowledge of thermal energy/matter interactions, explain the reason why feature B and D in Question 1 are bright, respectively. (Hint, the reasons for the B and D are different.) (2 point)

Sacramento, CA UHIPP Image

California’s capital city has diverse land cover types resulting in unique thermal regimes shown in the false-color infrared on the right. In this “quick look” image which has not been calibrated with ground sensor data or corrected for atmospheric interference – - dark red are hot, and blue and green are cool.

This thermal image was formed, possibly by density slicing the thermal data, in the following manner:

        Red   		Hot- About 122 deg. C (140 deg. F)
        Orange     	
        Yellow   	
        Green  	
        Blue     		Cool – About 29-36 deg. C (85-96 deg. F)

6. Open the image sacramento.jpg (Choose file type “JFIF”) in ERDAS 2014, right click the image, and choose inquire box and to locate the land cover A by using the location information below.

(i) What is the land cover labeled A (1 point)?

(ii) Is this land cover cooler or warmer than the surrounding areas? Explain why (2 points)?

(iii) If a similar image were acquired at night, approximately at 10:00 pm, what differences if any, would you expect in the thermal characteristics of the land cover labeled A? (1 point)





(iv) What is the explanation for your answer in (iii) above? (1 point)

7. Land cover types labeled B and D are cultural features while C is a natural feature. (3 points) (Note you are working in map coordinates )

B C D

(i) Identify the features at the following locations:

B. ________________________________

C. ________________________________

D. ________________________________

(ii) Which land cover type(s) C and the features North (light blue) and east (dark blue) of C is the coolest and why? (2 points, hints: think about what the other two features are)

(iii) Which is the warmest: paved road, park, or river? Discuss the function of water and vegetation to modulate the surface temperature? (2 points)

8. Interstate 5, running north to south along the East side of the Sacramento River, and US 50, from left to the bottom right, are clearly visible on the images.

(i)What surface material (Asphalt, Bitumen or Concrete) was used in the construction of the two roads? (1 point)

(ii) Are these roads cooler or warmer than the area labeled as B? (1 point)

(iii) Provide an explanation for your answer in (ii) above. (1 point)

All you have to turn into blackboard for this week is the final image you created above.