Thermal sensors_thermal mapping_unit iv.pptx

thermal sensors

1. Thermal Sensors/ Thermal Mapping Unit IV

2. In thermal remote sensing, the invisible radiation patterns of objects are converted into visible images and these images are called thermograms or thermal images . Thermal images can be acquired using portable, hand-held or thermal sensors that are coupled with optical systems mounted on an airplane or satellite . Applications of thermal remote sensing in agriculture includes nursery and greenhouse monitoring, irrigation scheduling , plants disease detection, estimating fruit yield, evaluating maturity of fruits and bruise (damage) detection in fruits and vegetables.

3. Thermal remote sensing exploits the fact that everything above absolute zero (0 K ) emits radiation in the infrared range of the electromagnetic spectrum. Hence approximately 80% of the energy thermal sensors received in the thermal wavelength region is emitted by land surface, making surface temperature as the easiest variable to extract from the thermal infrared signal

4. Block diagram of Thermal imaging system Microcontroller Thermal (Infrared ) sensor Display unit for real time temperature distribution Save image in SD card Wireless transmission Display thermal image on PC Digital Image Processing to identify abnormalities

5. An infrared thermal imaging system comprises of a thermal camera equipped with infrared detectors, a signal processing unit and an image acquisition system. Thermal imaging systems are evaluated on their thermal sensitivity , scan speed, image resolution, and intensity resolution Thermal remote sensing differs from optical remote sensing by measuring emitted radiations from the surface of the target object. Whereas optical remote sensing measures reflected radiations of the target object under consideration 8 - 14 µm regions have been of greatest interest for thermal remote sensing

6. pplications of Thermal Imaging The A rmal profile of seeds can be used to detect subtle(fine) changes in temperature These changes vary with viability. (capability) T his enables the classification and separation of viable seeds from non-viable ones Thermal Infrared (TIR) part of the spectrum is more sensitive to determine water stress (lack of available moisture) than other reflectance in visible, Near Infrared wavelengths.

7. Methods of using Thermal Infrared to assess spatial variation in soil water availability also have utility in precision agriculture applications It is also used for irrigation scheduling Soil salinity causes severe environmental degradation that obstructs crop growth. Soil salinity information can be extracted from thermal imageries as emitted radiance can provide subsoil information while reflected radiation cannot.

8. During plant pathogen infection, the physiological state of the infected tissue is changed. Changes in photosynthesis, transpiration, stomatal conductance (minute opening in epidermis of leaves, stems and other plant organs) and even cell death can occur Digital Infrared Thermography has the potential to identify and quantify disease control and associated pathogens

9. Thermal imaging can be used to estimate yield as thermography is based on sensing an object's own heat radiation . Maturity of fruits and vegetables can be estimated by thermal imaging and even different varieties could be identified if they are of the same ripeness. Detailed thermal analyses of the transpiration (exhalation of water vapour through stomata) behavior of the produce and its interrelation with the environment allow the determination of the optimal harvest date and the adapted design of postharvest machinery

10. Bruises and scratches are the most common forms of damage on the surface of fruits and vegetables during transportation and handling. Bruising is defined as damage of fruit tissue as a result of external forces which cause physical changes of texture or chemical changes of color, smell and taste Thermal imaging is a potential technique for bruise detection