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Remote Sensing from Space

Remote Sensing from Space

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Remote Sensing from Space

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  1. Remote Sensing from Space C5646

  2. Course Layout • Lectures • Practicals • Assessment

  3. Lectures Week 1 Introduction, course layout Week 2 The electromagnetic energy, energy source, wave theory, particle theory, Week 3 The electromagnetic spectrum Week 4 Radiation and the atmosphere, spectral signature

  4. Lectures Week 5 Image display, sensors and platforms Week 6 Spectral Resolution, spatial resolution, temporal resolution Week 7 Test No. 1 Remotely sensed images, multispectral images, type of images Week 8 Passive sensors, active sensors

  5. Lectures Week 9 Image Interpretation and analysis, visual interpretation, element of visual interpretation Week 10 Digital image processing, preprocessing, image enhancement Week 11 Image transformation, image classification and analysis Week 12 Image classification, information and spectral classes

  6. Lectures Week 13 Supervised classification, unsupervised classification Week 14 Test No. 2 Radar, basic principles, radar system in remote sensing Week 15 Range resolution, radar geometry, radar images

  7. Practicals • Digital Image Processing Print : intro_e.pdf exerc_e.pdf Hands-on assignments to be handed in before week 14 • Project Proposal Assigment see AssignX.pdf Date Due : week 8

  8. Practicals • Digital Image Processing Print : intro_e.pdf exerc_e.pdf Hands-on assignments to be handed in before week 14 • Project Proposal Assigment see AssignX.pdf Date Due : week 8

  9. Assesment • Test 2x 30% • Coursework (2) 20% • Final Exam 50% Total 100%

  10. Remote Sensing Remote Sensing is the acquisition and measurement of data/information on some property(ies) of a phenomenon, object, or material by a recording device not in physical, intimate contact with the feature(s) under surveillance; Techniques involve amassing knowledge pertinent to environments by measuring force fields, electromagnetic radiation, or acoustic energy employing cameras, lasers, radio frequency receivers, radar systems, sonar, thermal devices, and other instruments.

  11. Remote Sensing • Remote Sensing: The techniques for collecting information about an object and its surroundings from a distance without contact • Components of Remote Sensing: • the source, the sensor, interaction with the Earth’s surface, interaction with the atmosphere

  12. Mechanisms

  13. Remote Sensing Principle

  14. Some Basic Terms • Spectral response is a characteristic used to identify individual objects present on an image or photograph • Resolution describes the number of pixels you can display on a screen device • Spatial resolution is a measure of the smallest separation between two objects that can be resolved by the sensor

  15. The First Application of Remote Sensing

  16. A Brief Chronology of Remote Sensing 1826 - The invention of photography 1960’s - The satellite era, and the space race between the USA and USSR. 1960’s- The setting up of NASA. 1960’s - First operational meteorological satellites 1960’s - The setting up of National Space Agencies

  17. A Brief Chronology of Remote Sensing 1970’s - Launching of the first generation of earth resource satellites 1970’s - Setting up of International Remote Sensing Bodies 1980’s- Setting up of Specific Remote Sensing Journals - Continued deployment of Earth Resource satellites by NASA 1990’s - Launching of earth resource satellites by national space agencies and commercial companies

  18. A Brief Chronology of Remote Sensing • Satellite remote sensing first received operational status in 1966 in the study of meteorology. • At this stage a series of orbiting and geo-stationary American satellites were inaugurated, with the intention that they would yield information to any suitably equipped and relatively modestly priced receiver anywherein the world.

  19. Wave Theory Electromagnetic radiation consists of an electrical field (E) which varies in magnitude in a direction perpendicular to the direction in which the radiation is travelling, and a magnetic field (M) oriented at right angles to the electrical field. Both these fields travel at the speed of light (c)

  20. Wavelength and Frequency • Wavelength is measured in metres (m) or some factor of metres such as: • nanometers (nm, 10-9 metres), • micrometers (m, 10-6 metres) or • centimetres (cm, 10-2 metres). • Frequency refers to the number of cycles of a wave passing a fixed point per unit of time. Frequency is normally measured in hertz (Hz), equivalent to one cycle per second, and various multiples of hertz.

  21. Wave Theory From basic physics, waves obey the general equation: c = v l Since c is essentially a constant (3 x 108 m/sec), frequency v and wavelength l for any given wave are related inversely, and either term can be used to characterise a wave into a particular form.

  22. Particle Theory Particle (Quantum) theory suggests that EM radiation is composed of many discrete units called photons or quanta. The energy of a quantum is given as: Q = h.v where: Q = energy of a quantum (Joules - J) h = Planks constant, (6.626 x 10-34 J/sec) v = frequency

  23. Particle Theory We can combine the Wave and Particle theories for EM radiation by substituting v = c/l in the above equation. This gives us: Q = h.c l From this we can see that the energy of a quantum is inversely proportional to its wavelength. Thus, the longer the wavelength of EM radiation, the lower its energy content.

  24. Particle Theory This has important implications for remote sensing from the standpoint that: • Naturally emitted long wavelength radiation (e.g. microwaves) from terrain features, is more difficult to sense than radiation of shorter wavelengths, such as emitted thermal IR. • Therefore, systems operating at long wavelengths must “view” large areas of the earth at any given time in order to obtain a detectable energy signal

  25. Electromagnetic Spectrum

  26. Electromagnetic Spectrum • The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x-rays) to the longer wavelengths (including microwaves and broadcast radio waves). • There are several regions of the electromagnetic spectrum which are useful for remote sensing.

  27. Visible Spectrum • The light which our eyes - our "remote sensors" - can detect is part of the visible spectrum. • It is important to recognise how small the visible portion is relative to the rest of the spectrum. • There is a lot of radiation around us which is "invisible" to our eyes, but can be detected by other remote sensing instruments and used to our advantage.

  28. Visible Spectrum • The visible wavelengths cover a range from approximately 0.4 to 0.7 m. • The longest visible wavelength is red and the shortest is violet. • It is important to note that this is the only portion of the EM spectrum we can associate with the concept of colours.

  29. VIOLET:0.400 - 0.446mmBLUE: 0.446 - 0.500 mmGREEN:0.500 - 0.578 mmYELLOW:0.578 - 0.592 mmORANGE:0.592 - 0.620 mmRED:0.620 - 0.700 mm

  30. Visible Spectrum • Blue, green, and red are the primary colours or wavelengths of the visible spectrum. • They are defined as such because no single primary colour can be created from the other two, but all other colours can be formed by combining blue, green, and red in various proportions. • Although we see sunlight as a uniform or homogeneous colour, it is actually composed of various wavelengths. • The visible portion of this radiation can be shown when sunlight is passed through a prism,

  31. Infrared(IR)Region • The IR Region covers the wavelength range from approximately 0.7 m to 100 mm - more than 100 times as wide as the visible portion! • The infrared region can be divided into two categories based on their radiation properties - the reflected IR, and the emitted or thermal IR.

  32. Reflected and Thermal IR • Radiation in the reflected IR region is used for remote sensing purposes in ways very similar to radiation in the visible portion. The reflected IR covers wavelengths from approximately 0.7mm to 3.0 mm. • The thermal IR region is quite different than the visible and reflected IR portions, as this energy is essentially the radiation that is emitted from the Earth's surface in the form of heat. The thermal IR covers wavelengths from approximately 3.0 mm to 100 mm.

  33. Microwave Region • The portion of the spectrum of more recent interest to remote sensing is the microwave region from about 1 mm to 1 m. • This covers the longest wavelengths used for remote sensing. • The shorter wavelengths have properties similar to the thermal infrared region while the longer wavelengths approach the wavelengths used for radio broadcasts.

  34. Radiation Emission

  35. Emission of Radiation from Energy Sources • Each energy/radiation source, or radiator, emits a characteristic array of radiation waves. • A useful concept, widely used by physicists in the study of radiation, is that of a blackbody. • A blackbody is defined as an object or substance that absorbs all of the energy incident upon it, and emits the maximum amount of radiation at all wavelengths. • A series of laws relate to the comparison of natural surfaces/radiators to those of a black-body:

  36. Stefan-Boltzmann Law All matter at temperatures above absolute zero (-273 oC) continually emit EM radiation. As well as the sun, terrestrial objects are also sources of radiation, though of a different magnitude and spectral composition than that of the sun. The amount of energy than an object radiates can be expressed as follows: M = s T4 M = total radiant exitance from the surface of a material (watts m-2) s = Stefan-Boltzmann constant, (5.6697 x 10-8 W m-2 K-4) T = absolute temperature (K) of the emitting material

  37. Stefan-Boltzmann Law • It is important to note that the total energy emitted from an object varies as T4and therefore increases rapidly with increases in temperature. • Also, this law is expressed for an energy source that behaves like a blackbody, i.e. as a hypothetical radiator that totally absorbs and re-emits all energy that is incident upon it…….actual objects only approach this ideal.

  38. Kirchoffs law • Since no real body is a perfect emitter, its exitance is less than that of a black-body. • Obviously it is important to know how the real exitance (M) compares with the black-body exitance (Mb) • This may be established by looking at the ratio of M/Mb, which gives the emissivity (e) of the real body. M = eMb Thus a black-body = 1, and a white-body = 0

  39. Weins Displacement law • Just as total energy varies with temperature, the spectral distribution of energy varies also. • The dominant wavelength at which a blackbody radiation curve reached a maximum, is related to temperature by Weins Law: l m = A T lm = wavelength of maximum spectral radiant exitance, mm A = 2898 mm, K T = Temperature, K

  40. Some Basic Terms Upon Striking an Object the Irradiance Will Have the Following Response: • Transmittance - some radiation will penetrate into certain surface media such as water • Absorptance - some radiation will be absorbed through electron or molecular reactions within the medium encountered • Reflectance - some radiation will, in effect, be reflected (and scattered) away from the target at different angles