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Remote Sensing Review

Remote Sensing Review . Lecture 1 January 21, 2005. What is remote sensing. Remote Sensing: remote sensing is science of acquiring, processing, and interpreting

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Remote Sensing Review

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  1. Remote Sensing Review Lecture 1 January 21, 2005

  2. What is remote sensing • Remote Sensing: remote sensing is science of • acquiring, • processing, and • interpreting images and related data that are obtained from ground-based, air-or space-borne instruments that record the interaction between matter (target) and electromagnetic radiation. • Remote Sensing: using electromagnetic spectrum to image the land, ocean, and atmosphere.

  3. Electromagnetic Spectrum Source: http://oea.larc.nasa.gov/PAIS/DIAL.html

  4. Ways of Energy Transfer Energy is the ability to do work. In the process of doing work, energy is often transferred from one body to another or from one place to another. The three basic ways in which energy can be transferred include conduction, convection, and radiation. • Most people are familiar with conduction which occurs when one body (molecule or atom) transfers its kinetic energy to another by colliding with it (physical contact). This is how a pan gets heated on a stove. • In convection, the kinetic energy of bodies is transferred from one place to another by physically moving the bodies. A good example is the convectional heating of air in the atmosphere in the early afternoon (less dense air rises). • The transfer of energy by electromagnetic radiationis of primary interest to remote sensing because it is the only form of energy transfer that can take place in a vacuum such as the region between the Sun and the Earth. Jensen, 2000

  5. Wave model of EMR • Electromagnetic wave consists of an electrical field (E) which varies in magnitude in a direction perpendicular to the direction in which the radiation is traveling, and a magnetic field (M) oriented at right angles to the electrical field. Both these fields travel at the speed of light (c). Jensen, 2000

  6. Three characteristics of electromagnetic wave • Velocity is the speed of light, c=3 x 108 m/s • wavelength (ג) is the length of one wave cycle, is measured in metres (m) or some factor of metres such as centimetres (cm) 10-2 m micrometres (µm) 10-6 m nanometres (nm) 10-9 m • Frequency (v) 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. unlike c and ג changing as propagated through media of different densities, v remains constant. Hertz (Hz) 1 kilohertz (KHz) 103 megahertz (MHz) 106 gigahertz (GHz) 109 The amplitude of an electromagnetic wave is the height of the wave crest above the undisturbed position Travel time from the Sun to Earth is 8 minutes

  7. Particle model of EMR • Sir Isaac Newton (1704) was the first person stated that the light had not only wavelike characteristics but also light was a stream of particles, traveling in straight lines. • Niels Bohr and Max Planck (20’s) proposed the quantum theory of EMR: Energy content: Q (Joules) = hv (h is the Planck constant 6.626 x 10 –34 J s) = c/v=hc/Q or Q=hc/  • The longer the wavelength, the lower its energy content, which is important in remote sensing because it suggests it is more difficult to detect longer wavelength energy Newton’s experiment in 1966

  8. Energy of quanta (photons) Jensen, 2000

  9. EMR details • (mm) • Red: 0.620 - 0.7 • Orange: 0.592 - 0.620 • Yellow: 0.578 - 0.592 • Green: 0.500 - 0.578 • Blue: 0.446 - 0.500 • Violet: 0.4 - 0.446 Bees and some other insects can see near UV. The Sun is the source of UV, but only > 0.3 mm (near UV) can reach the Earth.

  10. EMR details (2)

  11. Source of EMR • All objects above absolute zero emit electromagnetic energy, including water, soil, rock, vegetation, and the surface of the Sun. The Sun represents the initial source of most of the electromagnetic energy remote sensing systems (except radar and sonar) • Total radiation emitted M (Wm–2) = σT4 (Stefan-Boltzmann Law), where T is in degrees K and σ is the “Stefan-Boltzmann” constant, 5.67×10–8 K–4Wm–2 -- Energy at Sun enormous, 7.3×107 Wm–2, reduced to 459 Wm–2 by Earth-Sun distance • Wavelength λmax of peak radiation, in μm = 2897/T (Wien’s Displacement Law) Examples: -- Peak of Sun’s radiation λmax = 2897/6000 = 0.48 μm -- Peak of Earth’s radiation λmax = 2897/300 = 9.7 μm Jensen, 2000

  12. Jensen, 2000

  13. Paths and Interactions If the energy being remotely sensed comes from the Sun, the energy: • is radiated by atomic particles at the source (the Sun), • propagates through the vacuum of space at the speed of light, • interacts with the Earth's atmosphere (3A), • interacts with the Earth's surface (3B), • interacts with the Earth's atmosphere once again (3C), • finally reaches the remote sensor where it interacts with various optical systems, filters, emulsions, or detectors (3D). 60 miles or 100km Jensen, 2000

  14. Several concepts • Planck’s equation - if a blackbody transforms heat into radiant energy, then the radiation received at a sensor is given by Planck’s equation. • Spectral Emissivity

  15. EMR EMR • Spectral reflectivity is the percentage of EMR reflected by the object in a each wavelength or spectral bands • Albedo is ratio of the amount of EMR reflected by a surface to the amount of incident radiation on the surface. Fresh Snow has high albedo of 0.8-0.95, old snow 0.5-0.6, forest 0.1-0.2, Earth system 0.35 EMR

  16. Remote sensing platforms

  17. Ground and Aircraft Based • Ground • repeat or continuous sampling • regional or local coverage • example: NEXRAD for precipitation • Aircraft • repeat sampling , any sampling interval • regional or local coverage • examples: AVIRIS for minerals exploration LIDAR for ozone and aerosols

  18. Space Based • Sun-synchronous polar orbits • global coverage, fixed crossing, repeat sampling • typical altitude 500-1,500 km • example: MODIS, Landsat • Low-inclination, non-Sun-synchronous orbits • tropics and mid-latitudes coverage, varying sampling • typical altitude 200-2,000 km • example: TRMM • Geostationary orbits • regional coverage, continuous sampling • over equator only, altitude 35,000 km • example: GOES

  19. Passive: source of energy is either the Sun, Earth, or atmosphere Sun - wavelengths: 0.4-5 µm Earth or its atmosphere - wavelengths: 3 µm -30 cm Active: source of energy is part of the remote sensor system Radar - wavelengths: mm-m Lidar - wavelengths: UV, Visible, and near infrared Types of remote sensing

  20. Measurement scales constrained by physics and technology • Spatial resolution (IFOV/GSD) and coverage (FOV) • Optical diffraction sets minimum aperture size • Spectral resolution (Dl) and coverage (lmin to lmax) • Narrow bands need bigger aperture, more detectors, longer integration time • Radiometric resolution (S/N, NEDr, NEDT ) and coverage (dynamic range) • Aperture size, detector size, number of detectors, and integration time • Temporal resolution (site revisit) and coverage (global repeat) • Pointing agility, period for full coverage

  21. Basics of Bit • Computer store everything in 0 or 1 (2bits) Bit no. 0 256 8 bits as an example

  22. The size of a cell we call image resolution, depending on… Such as 1 m, 30 m, 1 km, or 4 km

  23. Digital Image Data Formats • Each band of image is stored as a matrix (array) format; • To efficiently handle the multi-bands (and hyperspectral) imagery in an image processing software, BSQ (band sequential), BIL (band interleaved by line), BIP (band interleaved by pixel) are common image data format (see an example in p103 of the text book) .

  24. Procedures of image processing • Preprocessing • Radiometric correction is concerned with improving the accuracy of surface spectral reflectance, emittance, or back-scattered measurements obtained using a remote sensing system. Atmospheric and topographic corrections • Geometric correction is concerned with placing the above measurements or derivativeproducts in their proper locations. • Information enhancement • Point operations change the value of each individual pixel independent of all other pixels • Local operations change the value of individual pixels in the context of the values of neighboring pixels. • They are image reduction, image magnification, transect extraction, contrast adjustments (linear and non-linear), band ratioing, spatial filtering, fourier transformations, principle components analysis, and texture transformations • Information extraction • Post-classification • Information output • Image or enhanced image itself, thematic map, vector map, spatail database, summary statistics and graphs

  25. Remote Sensing Applications • Land: rocks, minerals, faults, land use and land cover, vegetation, DEM, snow and ice, urban growth, environmental studies, … • Ocean: ocean color, sea surface temperature, ocean winds, … • Atmosphere: temperature, precipitation, clouds, ozone, aerosols, …

  26. Applications driving remote sensing Jensen, 2000 Jensen, 2000 Various application demands as driving forces for the resolution improvements of remote sensing

  27. Trend and Future of Remote Sensing (1) • High spatial resolution - IKONOS launched in 1999 by Space Imaging (4 m multi-spectral and 1 m panchromatic) - QuickBird launched in 2001 by DIGITALGLOBE (2.44 m multi-spectral and 61 cm panchromatic) • High spectral resolution - AVIRIS, 10nm and 20 m, 224 bands - Hyperion launched in 2000, 10nm and 30m, 220 bands • High radiometric resolution - 8 bits to 12 bits • High temporal resolution - GOES 15-30 minutes - NEXRAD 6 or 10 minutes

  28. Trend and Future of Remote Sensing (2) • Globe coverage, high repeatability (or improved temporal resolution) - AVHRR, 1100m, morning or afternoon - MODIS, 250-1000m, morning or afternoon - NPOESS Preparatory Program (NPP) (to be launched 2007): 4 sensors - NPOESS (to be launched in 2009), 370-740m, 4 hours: 14 sensors • Real-time or near real-time availability - MODIS available online in the second day ? - NEXRAD available online in 6 minutes - NPOESS available online in 15 minutes • Cost free or affordable - Most of the federal collected images are free available or lower cost, while commercial high resolution images are affordable. • Integrated remote sensing and GIS - Remote sensing applications with the support of GIS - Remote sensing data as a major GIS data source

  29. Major image processing software • ENVI/IDL: http://www.rsinc.com/ • ERDAS Imagine: http://www.gis.leica-geosystems.com/Products/Imagine/ • PCI Geomatics: http://www.pci.on.ca/ • ER Mapper: http://www.ermapper.com/ • INTEGRAPH: http://imgs.intergraph.com/gimage/ • IDRIS: • Ecognition: http://www.definiens-imaging.com/ecognition/pro/40.htm • See5 and decision tree

  30. “Earth in a New Light” by NASA Earth Science Watch Movies (about half a hour)

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