Thermal remote sensing
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Thermal remote sensing measures the thermal infrared radiation emitted from surfaces, unlike optical remote sensing which measures reflected radiation. There are two primary thermal infrared windows between 3-5μm and 8-14μm where atmospheric absorption is low. Thermal remote sensing relies on kinetic heat, or internal temperature of objects, and radiant temperature, the external radiation emitted and detected at a distance. Emissivity is the ratio of radiation emitted by a surface to that of a blackbody and varies among materials, affecting apparent radiant temperature. Thermal data can be collected via scanning systems or push-broom arrays and used for applications like agriculture, natural hazards monitoring, border security, and urban heat island analysis.
Thermal remote sensing
- 1. THERMAL INFRARED REMOTE SENSING
- 2. INTRODUCTION Thermal Remote Sensing is the branch of remote sensing that deals with the acquisition, processing and interpretation of data acquired primarily in the thermal infrared(TIR) region of the Electromagnetic Spectrum. In thermal remote sensing we measure the radiation “emitted” from the surface of the target, as opposed to optical remote sensing where we measured the radiation ‘reflected’ by the target under consideration.
- 3. And the black areas in denote the region of spectrum where the atmosphere absorbs most of the infrared energy. Water vapor(H2O),CO2 and O3 are responsible for most of the absorption. In the Thermal Infrared region has two primary thermal infrared windows: 3-5µm. And 8-14µm.
- 4. Kinetic Heat, Radiant Temperature and Emissivity Thermal Remote Sensing it’s basically depends upon Kinetic Heat and Radiant Temperature.. Kinetic Heat All objects in the real world having a temperature above absolute zero. The energy of particles of molecular matter in random motion is called kinetic heat. Also it is called internal,real,or true heat. Concentration of kinetic temperature is measure by thermometer. Radiant Temperature/Energy The internal kinetic heat also converted to radiant energy, it is also called the external or apparent energy. We can utilize the “Radiometer” for measuring the Radiant temperature placed at a some distance from the object.
- 5. Fig. Radiant energy exiting. a) water, b) granite, c) dunite heated to 350K compared with a blackbody to the same temperature (Jensen,2003).
- 6. Emissivity The relationship between kinetic temperature and radiant temperature is not perfect. The remote measurement of the radiant temperature always less than the true kinetic temperature. So it is the ratio between of Radiant temperature and the True Kinetic temperature. Emissivity is differ by the different objects on the earth surface. Factors 1.Colour 2.Moisture content 3.Comcaction 4.Field of view 5.Wave length 6.Viewing angle 7.Surface Ruggedness Why do we need to know about Emissivity? Two objects laying next to one another (e.g:two rocks) could have the same kinetic temperature but different apparent/radiant temperature because their emissivities vary,,
- 7. Material Emissivity Clear water 0.98-0.99 Wet snow 0.98-0.99 Human skin 0.97-0.99 Rough ice 0.97-0.98 vegetation 0.96-0.99 Wet soil 0.95-0.98 Asphalt concrete 0.94-0.97 Brick 0.93-0.94 wood 0.93-0.94 Basalt rock 0.92-0.96 Dry mineral soil 0.92-0.94 paint 0.90-0.96 Dry Vegetation 0.88-0.94 Dry snow 0.85-0.90 Emissivity of the different objects-
- 8. Black Body • Blackbody is a theoretical construct that absorbs all the radiant energy striking it and radiates energy at the maximum possible rate per unit area at each wavelength for any given temp. • No objects in nature are true blackbodies. • Emissivity of blackbody is always ‘1’. • Several objects like clean water or deep water which are near to the blackbody concept. But they are not the black body.
- 9. Grey body • Its reflects a small fraction of the total energy stored by them • Its depends upon on the wavelength of different bands. Is a type of radiation emitted by a surface whose emissivity is distinctly varied for different wavelengths.. Selective Radiation
- 10. A)Spectral emissivity of a blackbody, a graybody and a selective radiator. B) Spectral radiance exitance distribution of the blackbody, graybody and hypothetical selective radiator.
- 14. THERMAL PORPERTIES OF TERRAIN
- 15. Thermal Infrared Data Collection Thermal infrared remote sensor data may be collected by: • across-track thermal scanners, and • push-broom linear and area array charge- coupled device (CCD) detectors.
- 16. across-track/whiskbroom thermal scanners • Use a rotating mirror to sweep along a line or a series of adjacent lines traversing the ground. • The incoming energy is separated into several spectral components that are independently sensed. • To separate thermal and non thermal energy forms
- 17. push-broom linear and area array charge-coupled device (CCD) detectors. • It is possible to make both linear and area arrays that are sensitive to mid- and thermal infrared radiation. • Linear array of detectors aligned across-track. • Image build up by satellite movement in flight direction. • No scanning mirror • 2D detector arrays can acquire multispectral or hyperspectral data.
- 18. Application Agricultural purpose Identification of water condition in the crop field. Estimation of moisture amount in the crop To find the appropriate time for irrigation Detect the different types of disease in the agricultural field Crop maturity time identification, etc. Identifying of natural hazard Volcanocity
- 19. Border security purposes Weather forecasting • Temperature • Pressure • Movement of the wind • Prediction of Amount of rainfall • Prediction of cyclone and tsunami • Prediction of cloudiness Others • Identification of building materials • Moisture condition of building • Coal mining identify. • Urban heat island effect.
- 20. URBAN HEAT ISLAND EFFECT An urban heat island (UHI) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities.
- 21. Thermal infrared image sources FLIR ATLAS LANDSAT ETM+ LANDSAT 8 OLI ASTER AVHRR COASTAL ZONE COLOUR SCANNER(CZCS) OCEANSAT(ISRO)
- 22. Reference