Thermal Edusat3

THERMAL REMOTE SENSING Dr. R.D. Garg [email protected]

• Earth-atmosphere system derives its energy from sun. • The earth’s surface and atmosphere radiate thermal energy outward owing to heating by solar irradiance.

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• Sensors that measure emitted radiation in the thermal region (infrared region) of the spectrum can produce very informative data about earth features. • Thermal Remote Sensing can be defined as ‘detection of remote objects by recording amount of thermal radiation emitted from various surfaces’. • All materials having a temperature above absolute zero (0 K or –273ºC) emit thermal energy both day and night.

IR region

: 0.7 - 300 µm

Reflected IR

: 0.7 - 3 µm (Photographic IR : 0.7 - 0.9 µm)

Near IR : 0.76 - 0.90 µm Mid IR (SWIR): 1.55 - 1.75 µm, 2.05 - 2.35 µm Thermal IR : 3 - 5 µm, 8 - 14 µm

Thermal Spectrum

• Thermal IR radiation is absorbed by glass lenses of conventional cameras and can’t be detected by photographic films. • Special optical-mechanical or electronic scanners are used to detect and record images in thermal IR region.

Kinetic heat – Kinetic energy of particles of matter in random motion. This internal or kinetic heat energy of matter is converted into radiant energy.

Kinetic temperature Tkin {measured by direct

contact}. Concentration of kinetic heat of a material.

Radiant temperature Trad {remotely measured}. Concentration of radiant energy of a body.

Trad = ( ε )¼ Tkin ™ RS sensors measure only Trad of the object

THERMAL PROPERTIES OF MATERIALS The primary objective of temperature measurements and related thermal response is to extract information about the nature, composition and other physical attributes of materials at the earth’s surface and in its atmosphere. Emissivity (ε) Thermal Inertia (P) Heat capacity (C) Thermal Conductivity (K) Thermal Diffusivity (Γ)

THERMAL PROPERTIES OF MATERIALS ‘Ratio of radiant energy emitted from a real body to radiant energy emitted from a reference black body’

Emissivity (ε)

0<ε ≤1

Thermal Inertia (P) Heat capacity (C) Thermal Conductivity (K) Thermal Diffusivity (Γ)

THERMAL PROPERTIES OF MATERIALS

‘measure of resistance offered by a substance in undergoing temperature Emissivity (ε) changes’

Thermal Inertia (P) Heat capacity (C) Thermal Conductivity (K) Thermal Diffusivity (Γ)

THERMAL PROPERTIES OF MATERIALS

‘amount of heat required to raise the temperature of a unit mass of substance by 1°C’ Emissivity (ε)‘ability of a substance to store heat’ ™ highest for water (1.01) Thermal Inertia (P)

Heat capacity (C) Thermal Conductivity (K) Thermal Diffusivity (Γ)

THERMAL PROPERTIES OF MATERIALS

Emissivity (ε)

‘rate at which heat is transferred within a substance through Thermal Inertia (P)conduction’ Heat capacity (C) Thermal Conductivity (K) Thermal Diffusivity (Γ)

THERMAL PROPERTIES OF MATERIALS

Emissivity (ε) Thermal Inertia (P)

‘rate at which heat is transferred within a substance through Heat capacity (C) diffusion’ Thermal Conductivity (K)

Thermal Diffusivity (Γ)

Thermal properties of various materials

Thermal properties of various materials Material Basalt Clay(moist) Concrete Copper Dolomite Glass Granite Gravel Gravel(sandy) Ice Iron Lead Limestone Marble Pumice (loose) Quartz Sand (dry) Shale Soil (sandy) Steel Water Wood

K Wm-1K-1 2.1 1.3 0.1 400.0 2.0 0.8 3.0 1.3 2.5 2.3 84.0 36.0 0.9 2.5 0.3

C 10 J kg-1 K-1 0.9 1.5 3.4 0.39 0.75 0.6 0.8 0.8 0.8 2.1 0.44 0.16 0.7 0.9 0.7

ρ 10 kg m-3 2.6 1.7 2.4 8.9 2.6 2.3 2.7 2.0 2.1 0.9 7.9 11 2.5 2.7 1.0

Γ 10 m2s-1 0.9 0.5 0.01 120.0 1.0 0.6 1.4 0.8 1.5 1.2 24.0 20.0 0.5 1.0 0.4

1000 Js m-2K-1 2.2 1.8 0.9 37.0 2.0 1.1 2.5 1.4 2.0 2.1 17.0 8.0 1.3 2.5 0.5

9.0 0.4 1.9 0.6 25.0 0.56 0.15

0.7 0.8 0.7 1.0 0.5 4.2 1.2

2.6 1.6 2.3 1.8 7.7 1.0 0.7

4.9 0.3 1.2 0.3 6.5 0.13 0.2

4.0 0.7 1.7 1.0 9.8 1.5 0.4

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ACQUISITION OF TIR INFORMATION Several instruments are available for the remote acquisition of surface information in TIR region. The majority of them are either Airborne or Spaceborne with a few field instruments.

Heat Capacity Mapping Mission (HCMM)10.5 - 12.5 µm; resolution 600 m Thermal Infrared Multispectral Scanner (TIMS) 6 bands between 8-12 µm

NOAA AVHRR 5 bands; resolution 1.1 km

Landsat Thematic Mapper (TM) band 6 10.4 - 12.5 µm; 60 m resolution

Advanced Spaceborne Thermal Emission Reflectance Radiometer (ASTER) (Terra) High resolution multispectral imager 3 bands in VNIR (0.5 - 1.0 µm); 15 m resolution 6 bands in SWIR (1.0-2.5 µm); 30 m resolution 5 bands in TIR (8-12 µm); 90 m resolution

Interpretation of Thermal Imagery

Temperature extremes, and heating and cooling rates can often furnish significant information about the type/condition of an object e.g., temp. curve for water is distinctive.

Interpretation of Thermal Imagery - evaporation - convective cooling

The thermal inertia of water is similar to that of soils and rocks, but during the day water bodies have a cooler surface temperature (S.T.) than soils and rocks. At night the S.T. are reversed with water becoming warmer than soils and rocks. Æ acquisition time should

be known, as the signatures vary during day and night

Interpretation of Thermal Imagery - transpiration - higher leaf-water content, insulation by dry leaves

Vegetation has a warm signature during nighttime and has cooler signature compared to adjacent soils during daytime.

Interpretation of Thermal Imagery - evaporative cooling, very high moisture in soil and vegetation

Damp Terrain shows less variation in day-time and night-time radiant temperature.

Interpretation of Thermal Imagery - high reflectivity, low emissivity, low radiant temperature

Metallic Objects show very less variation in day-time and night-time radiant temperature.

Applications of Thermal Infrared Remote Sensing Geology - differentiation of rock types, volcanic terrain, underground fires

Military - movement & concentration of troops Oceanography- SST (Sea Surface Temperature), PFZ (Potential Fishing Zone), oil spills, modeling climatic change

Agriculture - State of crops, ET (Evapotranspiration), soil moisture

Forestry - forest fires, their assessment and control, biomass burning

Thermal Images : Examples

Night-time (TM-6) thermal image of Lake Ontario and Erie

Day time

Night time

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