Thermal Infrared Remote Sensing. Lecture 7 October 16, 2007

Transcription

1 Thermal Infrared Remote Sensing Lecture 7 October 16, 2007

2 Thermal infrared of EM spectrum 100 µm 3.0 µm 0.7 µm All objects have a temperature above absolute zero (0 K) emit EM energy (in µm). Human being has normal 98.6 ºF (37 ºC) Our eyes are only sensitive to visible energy ( µm). Human sense thermal energy through touch. while detectors (sensors) are sensitive to all EM spectrum. All objects (vegetation, soil, rock, water, concrete, etc) selectively absorb solar shortwavelength energy and radiate thermal infrared energy.

3 Thermal infrared remote sensing measures: Land and ocean surface temperature, Atmospheric Temperature and humility Trace gas concentrations Radiation balance Emissivity

4 Kinetic heat, radiant flux and temperature, The energy of particles of matter in random motion is called kinetic heat (also referred to as internal, real, or true heat). We can measure the true kinetic temperature (T kin ) or concentration of this heat using a thermometer. - We perform this in situ (in place) temperature measurement when we are ill. - We can also measure the true kinetic internal temperature of soil or water by physically touching them with a thermometer. When these particles (have kinetic heat) collide they change their energy state and emit electromagnetic radiation called radiant flux (watts). The concentration of the amount of radiant flux exiting (emitted from) an object is its radiant temperature (T rad ). There is usually a high positive correlation between the true kinetic temperature of an object (T kin ) and the amount of radiant flux radiated from the object (T rad ). Therefore, we can utilize radiometers placed some distance from the object to measure its radiant temperature which hopefully correlates well with the object s true kinetic temperature. This is the basis of thermal infrared remote sensing. Unfortunately, the relationship is not perfect, with the remote measurement of the radiant temperature always being slightly less than the true kinetic temperature of the object. This is due to a thermal property called emissivity.

5 Planck equation Black body radiation (W m -2 µm -1 ) using Planck equation: We call T the physical (kinetic) temperature 2 ( 2πhc B λ, T ) = 5 hc / λkt λ ( e ) 1) λ K=( F-32)/

6 Not a perfect emitter

7 Emmisivity Emissivity spectrum is the ratio of radiance spectrum of a nonperfect emitter over that of a perfect emitter (blackbody) at the same temperature

8 Emmisivity used to identify mineral composition

9 Brightness temperature, and physical (surface) temperature Through radiance recorded by a remote sensor, if we use the Planck equation, we can get a temperature, which we call brightness temperature T b, which is less than the real physical (or surface) temperature T πhc 2πhc L( λ, Tb ) = = ε (, ) = 5 hc / kt ) λ B λ T ε λ λ b 5 hc / λkt ) λ ( e 1) λ ( e hc T = hc / kλtb kλ ln(1 ε λ + ε λ e ) 1) h, Planck s constant =6.626 x Ws 2 T, Kelvin (K) c, 3 x 10 8 m/s k, Boltzmann s constant=1.38 x Ws/K L or B, radiance (Wm -2 µm -1 ) c1=2πhc 2 =3.74 x Wm 2 c2=ch/k= mk

10 Thermal Radiation Raw Blackbody (perfect absorber and emitter) Stenfan-Boltzmann Law (M B = σt 4 in Wm -2 ) Wien s Displacement Law (λ max = 2898/T) Emissivity (ε = M R / M B ) at the same temperature M B = σt 4 kin M R = σt 4 rad ε = M R / M B = T rad4 / T 4 kin The dominant wavelength (λ( max ) provides valuable information about which part of the thermal spectrum we might want to sense in. For example, if we are a looking for 800 K forest fires that have a dominant wavelength of approximately 3.62 µm then the most appropriate remote sensing system might be a 3-5 µm thermal infrared detector. - MODIS band are in 3-5 µm. If we are interested in soil, water, and rock with ambient temperatures on the earth s surface of 300 K and a dominant wavelength of 9.66 µm, then a thermal infrared detector operating in the 8-14 µm region might be most appropriate. - Landsat image thermal band (6) is in µm - ASTER band 12 and 13 are in 8-14 µm - MODIS band and are in 8-14 µm

11 Diurnal Temperature Cycle of of Typical Materials The diurnal cycle cycleencompasses hours. Beginning at at sunrise, the the earth earth begins intercepting mainly short short wavelength energy (0.4 ( µm) µm) from from the the Sun. Sun. From about 6:00 6:00 am am to to 8:00 8:00 pm, pm, the the terrain intercepts the the incoming short short wavelength energy and and reflects much of of it it back back into into the the atmosphere where we we can can use use optical remote sensors to to measure the the reflected energy. However, some of of the the incident short short wavelength energy is is absorbed by by the the terrain and and then then re-radiated radiated back back into into the the atmosphere as as thermal infrared long long wavelength ength radiation (3 ( µm). The The outgoing longwave radiation reaches its its highest value during the the day day when the the surface temperature is is highest. This This peak k usually lags lags two two to to four four hours after after the the midday peak peak of of incoming shortwave radiation,, owing to to the the time time taken to to heat heat the the soil. soil. The The contribution of of reflected short short wavelength energy and and emitted ed long long wavelength energy causes an an energy surplus to to take take place during the the day. day. Both incoming and and outgoing shortwave radiation become zero zero after after sunset (except for for r light light from from the the moon and and stars), but but outgoing longwave radiation continues all all night.

12 Peak Period of of Daily Outgoing Longwave Radiation and the Diurnal Radiant Temperature of of Soils and Rocks, Vegetation, Water, Moist Soil and Metal Objects Temperature At the thermal crossover times, most of the materials have the almost same radiant temperature, it is not wise to do thermal remote sensing. Water and vegetation have higher thermal capacity. In different time of thermal images, there are different performances even the materials.

13 Kirchoff s radiation law Φ iλ = Φr λ + Φτ λ + Φα λ 1 = r λ + τ λ + α λ Kirchoff found in the infrared portion of the spectrum α λ = ε λ : good absorbers are good emitters Most materials does not lose any incident energy to transmittance, i.e. τ λ = 0, so we can get 1 = r λ + α λ = r λ + ε λ (or A + ε) This means reflectivity and emissivity has a inverse relationship: good reflectors are poor emitters

14 NASA s Earth Observing System missions with Thermal IR capability Landsat systems (MSS, TM, ETM+) ETM+ has a 60 m band at µm) TRMM CERES EOS Terra (Dec. 1999) CERES, MODIS, ASTER, MOPITT EOS Aqua (May 2002) AIRS, CERES, MODIS EOS Aura (July 2004) HIRDLS, TES

15 Source: Jeff Dozier

16 Source: Jeff Dozier

17 Source: Jeff Dozier

18 Source: Jeff Dozier

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20 Source: Jeff Dozier

21 Source: Jeff Dozier

22 MODIS land surface temperature and emissivity product led by Dr. Wan

23 Calibration and validation of MODIS T and E in Sevilleta, NM

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26 Urban Heat Island of San Antonio downtown area detected by MODIS temperature product 2:30 pm (CDT), July 14, 2004 T(K) X profile Y Profile NW-SE Profile NE-SW Profile Xie and Ytuarte, Distance (pixel)

27 Urban Heat Island of San Antonio downtown area detected by MODIS temperature product 2:00 am (CDT), July 15, 2004 X Profile Y Profile NW-SE NE-SW T (K) Xie and Ytuarte, 2005 Distance (pixel)

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30 Source: Jeff Dozier

31 Active fire detection: MODIS fire and thermal anomalies products Image caption: Fires in the Bahamas, Florida and Cuba (03 April 2004, 18:30 UTC) identified using MODIS Aqua and outlined in red on the MODIS 1km corrected reflectance product

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33 Source: Jeff Dozier

34 NASA Mars missions with Thermal IR capability Mars global surveyor Launched 11/1996. landed 12/1997, 3/1999 began have maps TES (6-50 µm) Mars Odyssey Launched 4/7/2001, landed 10/24/2001 THEMIS (5 visible at 18m, 10 thermal ( µm) at 100m) Mars Spirit Rover Launched 6/10/2003, landed 1/3/2004 Mini-TES Mars opportunity Rover Launched 7/7/2003, landed 1/24/2004 Mini-TES

35 What is TES? Thermal Emission Spectroscopy Michelson Interferometer, is the thermal IR portion of TES, covers the 6-50 µm ( cm -1 ) wavelength range, with spectral sampling 5 and10 cm -1 (spectral resolution ~10-20 cm -1 ), 286 or 142 bands Bolometric thermal radiance channel (5.5 to ~100 µm) Solar reflectance channel (0.3 to 2.7 µm ), to measure the brightness of reflected solar energy

36 MGS - TES Entered Mars orbit on board the MGS on Sep.11,1997

37 How does TES determine surface composition? Mixed Spectra Rocks are a mixture of minerals Emissivity spectrum from individual components of a mixture add together in a simple linear fashion. The linearity of the mixed spectrum allows it to be deconvolved.

38 Two distinct surface types found on Mars Type 1 - Similar to Basalt Type 2 Andesite? ( < 52 wt% SiO 2 ) ( wt% SiO 2 ) Mostly in southern highlands Mostly in northern lowlands (note the larger percentage of high silica glass is the main diff.) Bandfield et al. (2000), Hamilton et al. (2001)

39 MGS TES Basalt Map Basalt (Type 1 spectra) concentrated in Southern Highlands Bandfield et al. (2000), Hamilton et al. (2001)

40 MGS TES Andesite Map Andesite (type 2 spectra) appears concentrated in Northern Lowlands, but also intermixed with basalt in Southern Highlands. Bandfield et al. (2000), Hamilton et al. (2001)

41 Mars Hematite detected by TES

42 Rocks at the Mars Opportunity Rover landing site (on 1/24/2004, launched 7/7/2003)

43 NOAA and other missions with Thermal IR capability GOES (NOAA) (4 km), (8 km), (4 km), and (4 km) AVHRR (NOAA) , , all in 1.1 km NPOESS (joint NOAA/NASA/DoD) Middle-wave thermal 8 bands, long-wave thermal 4 bands m

44 One application: detection of loss of heat from buildings due to faulty insulation

45 Typical IR imagery of Heat Loss in Residential Structures 43.0 F Furnace Vent Vent Duct F

46 Energy Gain (Floor Leak) Missing Insulation in Vaulted Ceiling Area Heat Loss Heat Loss Moisture

47 Typical Institutional Building Heat Loss Typical Air Leak Patterns

48 Typical air in-leakage at doors Apartment balcony door during the summer the A/C system reads a slight positive pressure but this building is under a negative pressure, bringing in warm, moist air into the building through walls, doors, ceilings and under the floor system. Typical pattern of air in-leakage Typical pattern of air in-leakage

49 Air Leakage from noninsulated areas and window frames.