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BASICS OF REMOTE SENSING

BASICS OF REMOTE SENSING. Developed By Dr. Mohamed A. Mohamed With assistance from Ms. Sungmi Park Pixoneer Geomatics Inc. Phone: (703) 852 2162 E-mail: mmohamed@pixoneer.com Summer 2003. LECTURE 1. Introduction to Remote Sensing. Energy Source. Data Acquisition. Receiver. Maps.

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BASICS OF REMOTE SENSING

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  1. BASICS OF REMOTE SENSING Developed By Dr. Mohamed A. Mohamed With assistance from Ms. Sungmi Park Pixoneer Geomatics Inc. Phone: (703) 852 2162 E-mail: mmohamed@pixoneer.com Summer 2003

  2. LECTURE 1 Introduction to Remote Sensing

  3. Energy Source Data Acquisition Receiver Maps Image Atmosphere The selection tools ordinarily make hand edged selections, as if the selections were cut with a razor-sharp knife. Thus, when selections made with these tools are cut or pasted into an image, the individual pixels along the border cna be seen very clearly. This often results in an image that appears unatural. By defining a feather edge around a selection, you can cut and paste the selection without making it stand out dramatically from its surroundings. In this section you will define a feather edge, or border, around a lassoed selection using the Lasso Options dialog box. Note that you can also define a feather edge for rectangular and elliptical marquee selections using the Feather command in the Select menu. The selection tools ordinarily make hand edged selections, as if the selections were cut with a razor-sharp knife. Thus, when selections made with these tools are cut or pasted into an image, the individual pixels along the border cna be seen very clearly. This often results in an image that appears unatural. By defining a feather edge around a selection, you can cut and paste the selection without making it stand out dramatically from its surroundings. In this section you will define a feather edge, or border, around a lassoed selection using the Lasso Options dialog box. Note that you can also define a feather edge for rectangular and elliptical marquee selections using the Feather command in the Select menu. Film Reports Photograph Tape Users and Decision Makers Geographic Information Systems Ground Reference CD-ROM Computer Earth Surface Features Data Products and Storage Image Interpretation and Analysis Products and Information Extraction Science & Software FROM IMAGE TO INFORMATION

  4. The science and art of obtaining information about features or phenomena from data acquired by a device that records reflected, emitted, or diffracted electromagnetic energy, and is not in direct contact with the features or phenomena under investigation. Science & Software DEFINITION OF REMOTE SENSING Partially adapted from Lillesand and Keifer, 2000

  5. Science & Software HISTORY OF REMOTE SENSING • Born in 1839, photography was first used in topographic surveying in 1840’s • First aerial photograph was taken from a balloon in 1858 • Three-Color photographic process was developed in 1861 • Invented in 1903, airplane was first used as a camera platform in 1909. • Aerial photography was extensively used for reconnaissance during World War I. • Photo interpretation and photogrammetric mapping techniques and instruments were greatly developed during World War II • The lunar missions in 1960’s marked the era of space imaging • First imaging satellites were launched in early 1970’s Adapted from Lillesand and Keifer, 2000

  6. Science & Software RADIATION PRINCIPLES • Basic Wave Theory • Electromagnetic Spectrum • Particle Theory • Sources of Electromagnetic Energy • Stephan Boltzmann Law • Blackbody Radiator • Wien’s Displacement Law

  7. Science & Software ELECTROMAGNETIC WAVE V = Frequency

  8. Science & Software BASIC WAVE THEORY • Electromagnetic energy travels at the speed • of light in a harmonic sinusoidal fashion • Wave frequency (v) is the number of peaks • passing a point in space per unit time • The wavelength (l) is the distance between • two successive Peeks

  9. Wavelength: Distance between two successive peaks Frequency: Number of peaks (crests) that pass a given point in space per unit time Amplitude: Height of peak Wavelength Amplitude 4 cycles 8 cycles Frequency 1 Second Science & Software WAVELENGTH AND FREQUENCY

  10. Angstrom (Å) = 10-10 m or one 10 billionth of a meter Nanometer (nm) = 10-9 m or one billionth of a meter Micrometer (µm) = 10-6 m or one millionth of a meter Millimeter (mm) = 10-3 m or one thousandth of a meter Centimeter (cm) = 10-2 m or one hundredth of a meter Decimeter (dm) = 10-1 m or one tenth of a meter Meters (m) = 100 m or one meter Kilometer (dm) = 103 m or one thousand meter Science & Software WAVELENGTH MEASUREMENT UNITS

  11. Hertz (Hz) = one cycle per second Kilohertz (KHz) = 1000 cycles per second Megahertz (MHz) = 106 Hz or million Hz Gigahertz (GHz) = 109 Hz or billion Hz Science & Software FREQUENCY MEASUREMENT UNITS

  12. Science & Software BASIC WAVE EQUATION C = lv Where: C = Speed of light l = Wavelength v = Wave frequency v is inversely related to l The longer the wavelength the lower the frequency

  13. Science & Software ELECTROMAGNETIC SPECTRUM

  14. Science & Software PARTICLE THEORY Electromagnetic radiation is composed of many discrete units called photons or quanta Q = hv Where: Q = Energy of a photon h= Planck’s constant v = Wave frequency

  15. Science & Software ENERGY/WAVELENGTH RELATIONSHIP C = lv ------ 1 Q = hv ------ 2 From Equation 1 & 2 Q = hC / l The photon energy is inversely related to l The longer the wavelength the lower its energy content

  16. Science & Software SOURCES OF ELECTROMAGNETIC ENERGY • The Sun • All matter at temperature above absolute • zero (zero degree K or -273 degree C) Examples are terrestrial objects

  17. Science & Software STEPHAN BOLTZMANN LAW M = s T4 Where: M = Total radiant from the surface s = Boltzmann constant T = Absolute temperature Total energy increases very rapidly with increase in temperature

  18. Science & Software BLACKBODY RADIATOR • A hypothetical ideal radiator that totally absorbs • and re-emits all energy incident upon it • All earth surface features are not ideal radiators

  19. Science & Software WIEN’S DISPLACEMENT LAW lm =A/T Where: lm = Wavelength of maximum spectral radiant A= Constant T = Absolute temperature Wavelength and temperature are inversely related

  20. Science & Software GRAPHICAL REPRESENTATION OF WIEN’S DISPLACEMENT LAW

  21. LECTURE 2 Energy Interaction with the Atmosphere and Earth Surface Features (Objects)

  22. Science & Software ENERGY INTERACTION WITH THE ATMOSPHERE & EARTH FEATURES Scattered Radiation Absorbed Radiation Incident Radiation Reflected Radiation Emitted Radiation Absorbed Radiation

  23. Science & Software REFRACTION • The bending of light when it passes from one medium to another due to differing densities • The index of refraction (n) is a measure of the optical density of a substance n = c / cn Where: c = speed of light in vacuum cn = speed of light in a substance

  24. Science & Software SCATTERING • Unpredicted diffusion of radiation by • particles in the atmosphere • Three types of scatter: - Rayleigh scatter - Mie scatter - Non-selective scatter

  25. Science & Software RAYLEIGH SCATTER • Atmospheric molecules and tiny particles are • much smaller in diameter than wavelength of • the interacting radiation - Example is a blue sky

  26. Science & Software MIE SCATTER • Atmospheric molecule and particle diameters • are equal to the wavelength of the interacting • radiation • Water vapor and dust are major causes

  27. Science & Software NON-SELECTIVE SCATTER • Atmospheric molecule and particle diameters • are much larger than the wavelength of the • interacting radiation • Water droplets scatter all visible and near-to-mid • infrared wavelengths equally - Examples are fog and white clouds

  28. Science & Software ABSORPTION • Effective loss of energy to atmospheric constituents • Absorption band is a range of wavelengths in the electromagnetic spectrum within which radiant energy is absorbed by a substance • Most efficient absorbers are: - Water vapor - Ozone - Carbon dioxide

  29. Science & Software ATMOSPHERIC WINDOWS Courtesy of NASA Goddard Space Flight Center

  30. Science & Software ENERGY INTERACTION WITHEARTH SURFACE FEATURES Energy incident on an element are reflected, absorbed, and/or transmitted EI (l) = ER (l) +EA (l) + ET (l) Where: EI (l) = Incident energy ER (l) = Reflected energy EA (l) = Absorbed energy ET (l) = Transmitted energy

  31. Science & Software ENERGY INTERACTION WITHEARTH SURFACE FEATURES EI (l) = Incident energy ER (l) = Reflected energy EA (l) = Absorbed energy ET (l) = Transmitted energy

  32. Science & Software ENERGY REFLECTION BYEARTH SURFACE FEATURES ER (l) = EI (l) - [EA (l) + ET (l)] The geometric manner in which objects reflect energy is a function of surface roughness • Specular reflector • Diffuse (Lambertian) reflector • In-between (near specular, spread, near diffuse) - Examples are earth surface features

  33. Science & Software SURFACE REFLECTANCE

  34. Science & Software IDEAL SPECULAR REFLECTOR Angle of Reflection Angle of Incidence r i i = r Flat Surface that Manifest Mirror-like Reflection

  35. Science & Software LAMBERTIAN SURFACE Uniform reflectance in all directions

  36. Science & Software DIFFUSE REFLECTION It contains information on the “color” of the reflecting surface In remote sensing, we are most often interested in measuring the diffuse reflectance properties of terrain (earth surface) features

  37. Science & Software SPECTRAL REFLECTANCE • The portion of incident energy that is reflected • It is often expressed as a percentage rl = ER (l) / EI (l) * 100 Where: rl = Spectral reflectance ER (l) = Reflected energy EI (l) = Incident energy

  38. Science & Software SPECTRAL REFLECTANCE CURVE Is a graph of spectral reflectance of an object as a function of wavelength

  39. Science & Software SPECTRAL REFLECTANCE CURVE 60 Green Red Blue Near IR 50 MSS 6 MSS 5 MSS 4 MSS 7 40 % Reflectance Dead grass 30 20 Dry bare soil 10 Green grass 0.5 0.6 0.7 0.8 1.1 Wavelength

  40. % reflection off surfaces at particular wavelengths 5 0 Natural Grass Percent Reflectance 4 0 3 0 2 0 Artificial Turf 1 0 0 B L U E G R E E N R E D I N F R A R E D 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 M i c r o n s V i s i b l e L i g h t Science & Software ALBEDO • Healthy natural grass has a high albedo in the Near Infrared (IR)region • Artificial turf has a low albedo in the Near Infrared (IR) region

  41. Science & Software SPECTRAL SIGNATURE CURVE Is a spectral response measured to assess the type and/or condition of the feature Main characteristic Tends to imply an absolute or unique pattern

  42. Science & Software SPECTRAL RESPONSE PATTERN Is the spectral reflectance or emittance of a terrain feature Main characteristics • Quantitative but not absolute • Distinctive but not unique

  43. Science & Software SPATIAL EFFECT Factors that cause the same type of feature at a given point of time to have different spectral characteristics at different locations Example • Same crop in different fields

  44. Science & Software TEMPORAL EFFECT Factors that change the spectral characteristics of a feature over time Example • Vegetation in different seasons

  45. Uniform energy source Science & Software IDEAL REMOTE SENSING SYSTEM • Non-interfering atmosphere • Series of unique energy/matter interactions • at the earth’s surface • A super sensor • A real-time data handling system • Multiple data users.

  46. Variable and non-uniform energy sources Science & Software REAL REMOTE SENSING SYSTEM • Interfering atmosphere • Energy/matter interactions at the earth’s surface are not unique • Sensors have limited spectral sensitivity • Data handling system have limited capabilities • Concerns and issues about multiple data usage

  47. LECTURE 5 Electromagnetic Energy Detection with Optical and Thermal Imaging Systems Concepts of resolution

  48. Science & Software SCANNER SYSTEMS Build up two-dimensional images of the terrain for a swath beneath the plane using either across-track (whiskbroom) scanning or along-track (pushbroom) scanning

  49. Science & Software WHISKBROOM SCANNING • Uses a set of detectors, each of which is designed to have its peak sensitivity at a specific wavelength • Uses a rotating mirror to scan the terrain along scan lines perpendicular to flight line • The scanner repeatedly measure energy on both sides of the platform • Successive scan lines (contiguous) compose a two-dimensional image

  50. Science & Software WHISKBROOM SCANNING Scanning Mirror Detectors Flight Direction Scanning Direction

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