CE6003 REMOTE SENSING TECHNIQUES AND GIS

1. CE6003REMOTE SENSING TECHNIQUES AND GIS Prepared by, Dr. P. SATHEES KUMAR, ASP / CIVIL MSEC – KILAKARAI.

2. UNIT 1 EMR AND ITS INTERACTION WITH ATMOSPHERE & EARTH MATERIAL

3. Definition of Remote Sensing • Most prominent technique of collecting information from a distance. The data collected from a distance is called remotely sensed data. • Definitions: • It is the science of acquiring information about the earth’s surface without actually being in physical contact with the surface. • It can also be defined as the science or technology by which the characteristics of objects of interest can be identified, measured or analyzed without direct contact. • It is the science and art of obtaining information about an object, area, or phenomena through the analysis of data acquired by a device that is not in contact with the object, area or phenomena under investigation. • It is the science and art of collecting information about objects, area or phenomena from distance without being in physical contact with them.

4. Concepts of Remote Sensing • Best example of Remote Sensing is the human eye. • The term remote sensing was first used in the US in the 1960s. With the introduction of Landsat – I, the first observation satellite launched in 1972, remote sensing became widely used. • Source of Remote Sensing data is the Electromagnetic radiation reflected or emitted from an object. The characteristics of objects can be determined using reflected or emitted EMR from the object. • According to laws of nature, Each object has its own unique and different characteristics of reflection or emission, depending upon different environmental conditions. Every object will reflect out energy in some specific wavelength. This concept is applied in Remote Sensing to identify objects. • Therefore, Remote Sensing is the technology to identify and understand the object or the environmental condition, through the uniqueness of the reflection or emission. • Thus, basically Remote Sensing data consists of collecting information on that specific wavelength of EMR leaving the object and measuring its intensity.

5. Concepts of Remote Sensing (Continued) • Device to detect the EMR reflected or emitted from an object is a Sensor. Eg: Cameras, Scanners, Radar. • Vehicle to carry the sensor is called a platform. Eg. Aircrafts or satellites. • Remote Sensing includes studying aerial photography and satellite imagery to identify objects. • Now-a-days, most natural resource mapping is done using remote sensing. • Aerial photography has been used to produce topographic maps such as forest maps, geological maps, land use maps and soil maps; detailed city maps. (easy for upgradation; these are formed fast). • Satellite-based systems can measure phenomena that change continuously over time and cover large and inaccessible areas. • Remote Sensing is similar to normal study of photographs, with the only difference that large scale photographs and images are analyzed.

7. Idealized Remote Sensing System 1. Energy Source 2. Propagation of energy through atmosphere 3. Energy interaction with earth’s surface features 4. Airborne/space borne sensors receiving reflected and emitted energy 5. Transmission of data to earth station and generation of data produce 6. Processing, interpretation and analysis 7. Application by users 4 1 5 2 3 6 7 (Simple figure will be given as xerox)

8. Electromagnetic Radiation • Source of Remote Sensing data. • Is a carrier of EM energy and has the characteristic of both wave motion and particle motion. • Characteristics as Wave motion: • EMR can be considered as a transverse wave with an electric field and a magnetic field, located at right angles to each other. • It travels in a vacuum of free space with the speed of light, c ~ 3 x 108 m/s. • (WAVE THEORY) c = λƒ Frequency in Hz Wavelength in m

9. Wave Theory c = λƒ Stefan–Boltzmannlaw M = σT4 The Wien's Displacement Law λmax = A/ T Particle Theory E = h c/λ

11. Principle of Remote Sensing • Remote Sensing employ EMR and to a great extent relies on the interaction of EMR with the matter. It refers to the sensing of EMR, which is reflected, scattered or emitted from the object. • The main principle underlying Remote Sensing is “All matter reflects, absorbs, penetrates and emits EMR in a unique way”. • Why does a leaf look green? Its because the chlorophyll in the leaf absorbs blue and red spectra and reflects the green spectrum. • This unique characteristic of matter is called its Spectral Characteristics. • From laws of nature, mainly 3 forms of interactions taking place based on which we are able to identify objects present on the surface of the earth. They are 1. Absorption (A) 2. Transmission (T) 3. Reflection (R) • What you are interested is only the final reflected energy from the matter after all the above processes.

12. Principle of Remote Sensing (Continued) • The proportion of each of the above will vary depending on the wavelength of energy incident and the material, composition as well as the condition of the matter. • Depending on that, matter will reflect EMR at a particular wavelength, which is thereby captured to help in identifying the matter from a set of several objects. • Eg: How are you able to identify different coloured chalks.

13. Electromagnetic Spectrum • Although Visible light is the most popular form of EMR, other forms also exist, that help in identifying objects that visible light cannot achieve. • That many wave forms including the Visible light form part of what is known as Electromagnetic Spectrum.

14. Major regions of the electromagnetic spectrum.

15. Electromagnetic Spectrum (Continued) • EMR regions used in Remote sensing are UV (0.3 – 0.4µm), visible light (0.4 – 0.7µm), near infrared and thermal infrared (0.7 - 14µm) and microwave (1mm – 1m). Wavelength regions and their application in Remote Sensing

16. ELECTROMAGNETIC ENERGY INTERACTIONS WITH THE ATMOSPHERE Absorption Ozone, carbon dioxide, and water vapour are the three main atmospheric constituents which absorb radiation. Scattering (a)Selective • Rayleigh scattering (< 0.1 µm) • Mie scattering (0.1 to 10 µm) (b) Non-selective (5 to 100 µm)

19. Atmosphericwindows Some wavelengths cannot be used in remote sensing because our atmosphere absorbs essentially all the photons at these wavelengths that are produced by the sun. In particular, the molecules of water, carbon dioxide, oxygen, and ozone in our atmosphere block solar radiation. The wavelength ranges in which the atmosphere is transparent are called atmospheric windows.

20. ELECTROMAGNETIC ENERGYINTERACTIONS WITH SURFACE OBJECTS

21. Spectral Signatures • All objects on the surface of the earth have spectral signatures. • Spectral signature is the distinctive set of distinguishable characteristics of the object. • It is defined by quantifying the reflectance characteristics of earth surface features by measuring the portion of incident energy that is reflected. This is known as spectral reflectance, given by the expression: ρ(λ) in percentage = ER (λ) / EI(λ) • All matter have their unique spectral reflectance. Based on this, objects are identified on a photograph or image and this forms the basis of Remote Sensing.

22. Spectral Signatures (Continued) • Vegetation has high reflectance in IR region. • Reflectance of Water is stronger only in the visible region. • Soil shows uniform reflectance throughout. However, the presence of moisture in soil will cause a decrease in its reflectance and thus, you can identify soil moisture content.

24. Spectral Signatures of Vegetation • Even though Visible region is suitable for identify vegetation, to identify the content of chlorophyll present in the plant, Near infrared is more suitable for vegetation surveys and mapping because such a steep gradient at 0.7-0.9 m is produced only by vegetation. • It can also be used to identify different types of plants. • In using visible light, it will only enable us to identify that it is a plant among many other objects.

27. Types of Remote Sensing • Based on Type of energy source • Passive Remote Sensing • Source is the sun. • Makes use of sensors that detect the reflected or emitted EMR from natural sources. • Active Remote Sensing • Makes use of sensors that detect reflected responses from objects that are irradiated from artificially generated energy source (Eg. Radar). • Based on Wavelength regions • Visible and reflective IR Remote Sensing • Source is the Sun. • Makes use of sensors that are sensitive to the visible and IR region of the EM spectrum. • Depends on reflectance of objects on the ground surface. • Affected by atmospheric obstacles like dust, smoke, clouds etc. • Cannot be used in the night.

28. Types of Remote Sensing (Continued) • Thermal IR Remote Sensing • The source of radiant energy used in Thermal IR remote sensing is the object itself. • Under normal temperature conditions, every objects emits radiation. • Thus, this remote sensing makes use of sensors sensitive to thermal energy. • Can be used in the night. • Microwave Remote Sensing • Used to measure MW radiation emitted from objects. • High penetration power, thus, Less affected by atmospheric obstacles, scattering, cloud etc. • Very useful in studying studying snow, rain, soil moisture as it cannot penetrate them. • It can help in determining the exact location of storm centres, measuring the speed of the storm, and notifying the public of areas of potentially severe weather. • All weather remote sensing. • Example: Precipitation radar, Doppler radar.

29. Some examples for your interest Visible region of the spectrum Infrared region of spectrum **Identify the variation in chlorophyll in the leaves of the tree

30. Using Visible and IR region of the spectrum

31. Using Visible and IR region of the spectrum

32. Precipitation Radar

33. REMOTE SENSING APPLICATION Tsunami Impact Before and after

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