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# Introduction to remote sensing

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Anna university syllabus covered Remote sensing and GIS

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• ### Introduction to remote sensing

1. 1. Introduction to Remote Sensing
2. 2. What is REMOTE SENSING ? REMOTE SENSING includes all methods and techniques used to gain qualitative and quantitative information about distant objects without coming into direct contact with these objects. Look-Look, NO Touch
3. 3. What is REMOTE SENSING ? Remote Sensing (RS) methods try to answer four basic questions:  HOW MUCH of WHAT is WHERE?  What is the SHAPE and EXTENT of ... ? (Area, Boundaries, Lineaments, ...)  Has it CHANGED?  What is the MIX of Objects
4. 4. What is REMOTE SENSING ? HOW MUCH of WHAT is WHERE?  WHAT: Type, Characteristic and Properties of Object. Eg. Water, Vegetation, Land; Temperature, Concentration, State of Development; Subtype, Species, Use of ... ; Includes determination of generic object type, character and property as well as it’s abstract meaning. => DATA INTERPRETATION
5. 5. What is REMOTE SENSING ? HOW MUCH of WHAT is WHERE? HOW MUCH: determine by simple COUNTING, measuring AREA covered or percentage of total area coverage. WHERE: Relate locations and area covered to either a standard map or to the actual location on the ‘ground’ where the object occurs.NOTE: WHERE also refers to a moment in time
6. 6. What is REMOTE SENSING ? What is the SHAPE and EXTENT of ... ? (Area, Boundaries, Lineaments, ...)This extends the ‘WHERE’ to be a completely GEOMETRIC problem. MAP PRODUCTION methods are to be applied to the analysis of RS information. These include: Photogrammetric Methods:Identification and Delineation of Boundaries and Lineaments (Roads, Rivers, Fault Lines)
7. 7. What is REMOTE SENSING ? Has it CHANGED?CHANGE may occur with progress of TIME.Change may be detected through comparison of observed states at different moments in time.=> CHANGE DETECTION
8. 8. What is REMOTE SENSING ?  What is the MIX of Objects? The surface of the Earth is covered by objects like Soil, Water, Grass, Trees, Houses, Roads and so on. These are ‘GENERIC OBJECTS’. We know these well, but we also know objects like Open Forest, Residential and Industrial Estates, etc. Each of these ABSTRACT OBJECTS are made up of a typical collection of Generic Objects.
9. 9. What is REMOTE SENSING ?  What is the MIX of Objects? One important task for Remote Sensing is to identify GENERIC OBJECTS as well as ABSTRACT OBJECTS within areas of interest The following lessons will be devoted to techniques and methods as well as to the logistic for finding answers to the four basic questions.
10. 10. What is REMOTE SENSING ?  Remote Sensing (Look- Look, No Touch) is a much wider field than we will discuss in this lecture series. We will Vision Medical Imaging concentrate on that part of RS dealing with  EARTH LAND RESOURCES Sound and Radio Wave Detection
11. 11. What is REMOTE SENSING ? What makes it tick ??? (1) RS requires a CARRIER of information, which can bridge distances. (2) RS requires a SENSOR which can detect changes in the carried Signal. (3) RS requires RECORDING, ANALYSIS, INTERPRETATION and REPRESENTATION of the sensed information in a purposeful way.
12. 12. What is REMOTE SENSING ? (1) RS requires a CARRIER of information, which can bridge distances. These Carriers of Information are FIELDS of FORCES: * Pressure Wave Fields of Sound, * Gravity Force Fields, * Magnetic Force Fields and * Electro-magnetic Force Fields. The latter are of our main interest, since they include visible and invisible LIGHT.
13. 13. What is REMOTE SENSING ?  (2) RS requires a SENSOR which can detect changes in the carried Signal. Apart from our own eyes and ears, technology has provided us with a multitude of sensors operating in the detection of force fields: microphones, geophones, photographic film, video cameras and photo detectors, radio wave receivers, gravimeters and magnetometers.
14. 14. What is REMOTE SENSING ? (3) RS requires RECORDING, ANALYSIS, INTERPRETATION and REPRESENTATION of the sensed information in a purposeful way. This is a technique based topic. It is essential for the success or failure of RS in respect of it’s anticipated purpose. This topic will be dealt with in it’s main aspects (but not completely) in the following lessons.
15. 15. What is REMOTE SENSING ? Sensor System eg. CameraSource of Force Field Resulting RS Data Set DATA eg. Image ACQUISITION Reflection Object (generic)
16. 16. What is REMOTE SENSING ? DATA PROCESSING Interpretation (secondary) Measurements Data Processing & Mapping (geometric) Presentation of Processing Results Explaining deduced OBJECT INFORMATION RS Data Set eg. Image Object(s)
17. 17. ER, the Physical Basis of RS Fraunhofer, Joseph (1877-1826), German optician and physicist, Spectroscopy Wien, Wilhelm (1864-1928), German physicist, 1911 Nobel Prize in Physics, Wien’s Displacement Law Planck, Max Karl Ernst Ludwig (1858-1947), German physicist, 1918 Nobel Prize in Physics, laid basis to Quantum Physics, developed Planck’s Law Einstein, Albert (18779-1955), German(?) physicist, 1921 Nobel Prize in Physics, General Theory of Relativity, and E = m c^2 Serious, Jahoo (still alive), son of Tasmanian apple grower,, How to put bubbles into beer: E = m c^2
18. 18. ER, the Physical Basis of RS  Fraunhofer discovered ‘black lines’ in the spectrum of light emitted by various superheated chemical elements. These lines Fraunhofer Lineswere as typical for each of the elements as fingerprints for humans.  Chemical Composition of objects effects emitted ER in a unique way for each element.(found empirically by observation)
19. 19. ER, the Physical Basis of RS In Einsteins formula E = mc^2 Fraunhofer Lines E = Energy m = mass (of matter/object) c = propagation velocity of light What does that tell us ?  There is a well defined relationship between MATTER, ENERGY and 2 ELECTROMAGNETIC E = mc RADIATION (eg. light)
20. 20. ER, the Physical Basis of RS The basic building blocks of all matter are ATOMS The basic building blocks of Atoms are the NUCLEUS (Neutrons and Protons) and several ELECTRONS. Electrons are thought to be spinning around the Nucleus at orbits of different, but well pre- defined discrete sequential radii.
21. 21. ER, the Physical Basis of RS Neutrons are thought to carry NO Energy charge. Protons are thought to carry a charge of energy defined as being positive. Electrons are thought to carry a charge of energy defined as being negative. Because of the dual polarity (positive <=> negative) an energy potential exists between Nucleus and Electrons
22. 22. ER, the Physical Basis of RS An equal number of Electrons and Protons exist in all atoms (isotopes excluded). A balance exists quasi mechanical between the attraction forces of opposite charges and centrifugal forces of the spinning Electrons. This balance is an intricate compromise of these forces and the actual energy level inherent to each atom.
23. 23. ER, the Physical Basis of RS The energy level contained in an atom can be changed (eg. by heating or cooling). The balance of forces inside the atom will automatically adept to energy level changes by moving electrons to higher or lower orbits.
24. 24. ER, the Physical Basis of RS To have an electron move from it’s current orbit to the next outer orbit, an energy amount equal to one Planck’s Quantum has to be added to the atom (eg. by heating). To have an electron drop back from an outer orbit to the next inner one, the same amount of energy has to be extracted from the atom.
25. 25. ER, the Physical Basis of RS It is this EXTRACTION of energy from an atom when electrons drop back to lower orbits which is of interest to us. One widely accepted theory says, that atoms lose energy in form of Electromagnetic RadiationEnergy differential = 1 Planck’s Quantum
26. 26. ER, the Physical Basis of RS Electromagnetic Radiation One theory explains ER as a WAVE field, another as a field of a stream of PHOTONS, particles so small that they have no mass. Both are said to propagate at Wave light speed. PhotonEnergy differential = 1 Planck’s Quantum E = mc^2
27. 27. ER, the Physical Basis of RSc = const ~ 300000 km/sec Electromagnetic Radiation  Some atoms may have been charged to a higher energy level; pushing electrons further than one orbital level. In turn they can drop back over more than one orbit level: more energy than one Quantum Wave PhotonEnergy differential = 1 Planck’s Quantum E = mc^2
28. 28. ER, the Physical Basis of RSc = const ~ 300000 km/sec2 Quantum charge Electromagnetic Radiation Gerd’s interpretation: Since c is constant, all photons travel about 300,000 km/sec Those with a higher energy charge will use a ‘more wiggly’ (thus, longer) wave path than those with lesser charge. Wave PhotonEnergy differential = 1 Planck’s Quantum E = mc^2
29. 29. ER, the Physical Basis of RS Electromagnetic Radiation Wave characteristics: λ λ = Wave length = distance between consecutive wave peaks (measured in µm) f = frequency = number of wave peaks (wiggles) in the wave train propagating for 1 sec (measured in Hz) λ=c/fc = const ~ 300000 km/sec
30. 30. ER, the Physical Basis of RS Electromagnetic Radiation Summing up: λ  High Energy Radiation proceeds at higher frequencies (shorter wavelength compared to low energy radiation.  Radiation wave length mix depends on amount of (heat) energy contain in an atom PLANCK’s LAWc = const ~ 300000 km/sec
31. 31. ER, the Physical Basis of RS PLANCK’s LAW λ Total Radiation Energy emitted Radiation Energy Curve for an object (BLACK BODY) at constant temperature. peak short longc = const ~ 300000 km/sec Wave Length λ
32. 32. ER, the Physical Basis of RS WIEN’s DISPLACEMENT LAW Total Radiation λ Energy emitted Radiation Energy Curves for an object (BLACK BODY) at various constant temperatures. 6000K 3000k 1000K 300K0K = -273 degree Celsius short long300K = 27 degree Celsius Wave Length λ
33. 33. ER, the Physical Basis of RS Using Fraunhofer’s Observations A Black Body is a theoretical, not a real object. λ Real Objects will produce somewhat different radiation output pattern. Radiation Energy Curve for an object at constant temperature. Gerd’s real object short longc = const ~ 300000 km/sec Wave Length λ
34. 34. ER, the Physical Basis of RS Using Fraunhofer’s Observations  The variation in Radiation output from a REAL OBJECT depends on it’s chemical composition. Water has a different SPECTRAL SIGNATURE than soil or chlorophyll containing leaf matter, etc. QUESTIONS: Radiation Energy Curve for • Can we use these facts to an object at constant temperature. measure object temperatures? • Can we use these facts to Gerd’s real identify the chemical object composition of objects and • can we use the latter to short long identify the object itself? Wave Length λ
35. 35. ER, the Physical Basis of RSThe Average Temperature ofWIEN’s DISPLACEMENT Earth’s Surface rarely LAW exceeds 300 K, an object Total Radiation temperature to low to Energy emitted Radiation Energy Curves for provide for EMITTED an object (BLACK BODY) RADIATION of sufficient at constant temperatures. strength to register on most 6000K of the available sensors 3000k (except in thermal IR). 1000K 300K (Even warm nights can be pitch black) short long Wave Length λ
36. 36. ER, the Physical Basis of RSThe surface of the Sun’s outer WIEN’s DISPLACEMENT  atmosphere (photosphere) LAW has a temperature of about Total Radiation 5800K, hot enough to Energy emitted Radiation Energy Curves for provide adequate radiation an object (BLACK BODY) energy. (Peak output in at constant temperatures. GREEN of visible light). 6000K 3000k Most RS systems utilise 1000K reflected sun light. 300K short long Wave Length λ
37. 37. ER, the Physical Basis of RS WIEN’s DISPLACEMENTQUESTION: Does incident LAW sun light interact in a Total Radiation similar way with matter as Energy emitted described is the case for Radiation Energy Curves for emitted radiation? an object (BLACK BODY) at constant temperatures.ANSWER: YES! 6000K ER (including light) is a form 3000k of energy (as is heat). Matter 1000K (atoms) can absorb as well as 300K emit energy. short long Wave Length λ
38. 38. ER, the Physical Basis of RSObjects under illumination by sun light will partially WIEN’s DISPLACEMENT absorb radiation. Total RadiationAbsorption level varies with Energy emitted wave length depending on Radiation Energy Curves for chemical composition of an object (BLACK BODY) the object at constant temperatures. 6000KRadiation not absorbed is 3000k mostly reflected and 1000K available for RS. 300KSpectral Signatures short long Wave Length λ
39. 39. ER, the Physical Basis of RS Examples of Spectral Signatures (not to exact scale; see Textbook) % Reflectance Vegetation (green) (of Sun Light) 50 Bare Soil (Grey/Brown) Water (clear) 0 µm(<= UV) 0.4 (blue) 0.5 (green) 0.6 (red) 0.7 (IR=>) 0.8 1.0
40. 40. ER, the Physical Basis of RS The Electromagnetic Spectrum (not to exact scale; see Textbook) Wave Length10^-6 10^-3 0.1 1 100 10^5 10^8 µ m (.... Sound not part of ER) Micro-γ -Rays X-Ray UV Wave TV/Radio Note: outside Thermal Infrared the visible Range, Visible Near & Mid Infrared no colours or shades will be Blue Green Red perceived. 0.4 0.5 0.6 0.7 µ m
41. 41. ER, the Physical Basis of RS The General Remote Sensing Radiation Model Source SI = Incident ER SensorR = Reflected SimplifiedA = Absorbed Radiation-T = Transmitted I BalanceS = Scattering I=R+A+T R R=I-A-T T A A
42. 42. ER, the Physical Basis of RS A bright Idea for RS % G R IR Vegetation (green) Reflectance (of Sun Light) Bare Soil (Grey/Brown) 50 Truth Table Veg. Soil G med med R low high IR high+ high 0 µm(<= UV) 0.4 (blue) 0.5 (green) 0.6 (red) 0.7 (IR=>) 0.8 1.0
43. 43. ER, the Physical Basis of RS Truth Table A bright Idea for RS Veg. Soil G med med R low high IR high+ high G R IR
44. 44. Landsat 7