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EE/Ae 157a Week 4: Visible and Near IR

EE/Ae 157a Week 4: Visible and Near IR. Topics to be Covered. Space Mirrors Diffraction limited resolution, Space mirror materials, Mirror coatings, structural materials Space Detectors Photoemissive, Photoconductive, Photovoltaic, CCDs Examples of Systems Landsat MSS and TM, SPOT

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EE/Ae 157a Week 4: Visible and Near IR

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  1. EE/Ae 157a Week 4: Visible and Near IR

  2. Topics to be Covered • Space Mirrors • Diffraction limited resolution, Space mirror materials, Mirror coatings, structural materials • Space Detectors • Photoemissive, Photoconductive, Photovoltaic, CCDs • Examples of Systems • Landsat MSS and TM, SPOT • Examples of Image Artifacts • Line Dropouts, Banding, Line Offsets • Analysis Techniques • Ratio images, Principal components, NDVI, Edge enhancements, Sharpening, Spectral unmixing, Classification

  3. Basic Remote Sensing System Source Detector Waves Emitted Scattering Object Collecting Aperture

  4. Imaging Terms Field-of-view Swath Width Dwell Time Along-Track Direction Cross-Track Direction

  5. Areal Image Plane Scanning Mirror Platform Movement “Point” Detector Imaging Optics Imaging Optics Along-Track Direction Swath Width Cross-Track Direction Line Array Detectors Imaging Optics Types of Imaging Systems (a) Framing Camera (b) Scanning System (c) Pushbroom System

  6. Comparison of Imaging Systems From Elachi,1987

  7. Primary Secondary Focal Plane Basic Telescope

  8. Diffraction Limited ResolutionCircular Aperture Rayleigh criterion for resolution:

  9. Telescope Classification From Space Remote Sensing Systems: An Introduction, by H.S. Chen, 1985

  10. Types of Telescopes Newtonian Ritchey-Critien Cassegrain Schwarzschild Gregorian Schmidt Dall-Kirkham From Space Remote Sensing Systems: An Introduction, by H.S. Chen, 1985

  11. Telescope Terms Focal Length: Effective length of the light path from the lens or mirror to the focus point Aperture Size: Unobstructed size of the lens or mirror Focal plane: The area covered with sensors that change electromagnetic energy into electrical signals Field of View: The angle viewed by the focal plane Pixel Field of View: The angle viewed by a single detector in the focal plane Field of Regard: The total angle that a scanning telescope can image

  12. Diffraction Limited ResolutionCircular Aperture Rayleigh criterion for resolution:

  13. Diffraction Limited ResolutionCircular Aperture Separation < 1.22 l/D Separation = 1.22 l/D Separation > 1.22 l/D

  14. Diffraction Limited ResolutionEffect of Wavelength

  15. Diffraction Limited ResolutionAperture Size for Constant Resolution Aperture Size in meters

  16. Diffraction Limited ResolutionEffect of Apodization NO APODIZATION GAUSSIAN SIGMA = RADIUS

  17. Diffraction Limited ResolutionEffect of Apodization NO APODIZATION GAUSSIAN SIGMA = RADIUS

  18. Diffraction Limited ResolutionEffect of Aperture Shape

  19. Diffraction Limited ResolutionEffect of Surface Errors NO ERRORS WAVELENGTH / 10

  20. Diffraction Limited ResolutionEffect of Surface Errors NO ERRORS WAVELENGTH / 10

  21. Diffraction Limited ResolutionEffect of Surface Errors NO ERRORS WAVELENGTH / 6.66

  22. Improving Angular Resolution Through Aperture Synthesis

  23. Improving Angular Resolution Through Aperture Synthesis LIGHT ADDED IN PHASE

  24. Improving Angular Resolution Through Aperture Synthesis LIGHT ADDED OUT OF PHASE

  25. Aperture SynthesisEffect of Aperture Spacing Spacing = 4 diameters Spacing = 8.5 diameters

  26. Space Mirror Materials From Space Remote Sensing Systems, by H.S. Chen

  27. Space Mirror Coatings Adapted From Space Remote Sensing Systems, by H.S. Chen

  28. Space Structural Materials From Space Remote Sensing Systems, by H.S. Chen

  29. Detectors • Electro-optical detectors transforms wave energy into electrical energy • The two most common types are thermal and quantum detectors • Thermal detectors rely on the increase in temperature in heat sensitive material due to absorption of incident radiation • Implementations include bolometers and thermocouplers • Thermal detectors are slow, have low sensitivity, and their response is independent of wavelength • Thermal detectors are not commonly used in modern remote sensing systems

  30. Detectors • Quantum detectors use the direct interaction of the incident photons with the detector material, which produces free charge carriers • They are typically classified into three categories: photoemissive, photoconductive, and photovoltaic • Quantum detectors have fast response and high sensitivity, but have a limited spectral response • Quantum detectors are characterized by a parameter

  31. Photoemissive Detectors • In photoemissive detectors, the incident radiation leads to electron emission from a photosensitive intercepting surface • The emitted electrons are accelerated and amplified • These detectors are primarily used at shorter wavelengths, since the incoming photons must have sufficient energy to overcome the binding energy of the electrons • Cesium has a cut-off wavelength of 0.64 microns • Composites, such as silver-oxygen-cesium have longer wavelength (1.25 microns) cut-off wavelength • An example of this type of detector is the Photomultiplier tube (PMT) • Landsat multi-spectral scanner (MSS) used PMT detectors for three of the four bands

  32. Photoconductive Detectors • In photoconductive detectors, photons with incident energy greater than the forbidden band energy gap in the semiconductor material produces free-charge carriers • This causes the resistance of the photosensitive material to vary inversely proportional to the number of incident photons • Exciting electrons across the forbidden band requires substantially less energy than electron emission, and consequently photoconductive detectors can operate at longer wavelengths • Back-biased silicon photodiodes operate in the photoconductive mode • Photodiodes can respond within a few nanoseconds • Landsat MSS band 4 used a photodiode as a detector.

  33. Photovoltaic Detectors • In the case of photovoltaic detectors, the incident energy is focused on a p-n junction, modifying the electrical properties, such as the backward bias current • Unbiased silicon photodiodes operate in the photovoltaic mode • Because this mode has no dark current, it has distinct advantages for low-level dc radiation signals • The photovoltaic response time is typically limited to a few microseconds

  34. 1-10 nm 10-100 nm 0.1-1 um 1-10 um 10-100 um 100-1000 um > 1 mm UV Vis NIR MIR FIR Sub-mm mmWave DetectorLandscape Commercial and defense applications in comms and radar • Primarily driven by space based astrophysics • weak infrastructure • limited funding • great science • SAFIR • Commercial and defense applications in terrestrial imaging and sensing • strong technical infrastructure • synergistic funding • strong technical infrastructure • synergistic funding SIS CMOS Uncooled Bolo TECHNOLOGIES Micro Channel Plate InGaAs QWIP HEB Schottky SC Calorimeter CCD HgCdTe Si: As SC Bolometer CCD Calorimeter GaN InSb Si: Sb Ge: Ga InP HEMT

  35. Charge Coupled Device (CCD) Detectors • CCD devices control the movement of signal electrons by the application of electric fields • Most CCD devices can operate in either the photoconductive or the photovoltaic modes • In monolithic CCDs the photon detection and multiplexing are performed on the same chip. It is best suited for VLSI technology, and have lower production costs • In hybrid CCDs these operations are performed by two separate chips. Splitting these operations means that each can be optimized separately • CCD detectors are easily integrated into arrays • Most modern remote sensing systems use CCD detectors. Examples include SPOT, MOMS and Galileo

  36. CCD Readout

  37. CCD Timing

  38. Example: Kodak CCDs Device Pixels (HxV) Pixel Size (H x Vµm) KAF-0261E 512 x 512 20.0 x 20.0 KAF-0401E(/LE) 768 x 512 9.0 x 9.0 KAF-1001E 1024 x 1024 24.0 x 24.0 KAF-1301E(/LE) 1280 x 1024 16.0 x 16.0 KAF-1401E 1320 x 1037 6.8 x 6.8 KAF-1602E(/LE) 1536 x 1024 9.0 x 9.0 KAF-3200E(ME) 2184 x 1472 6.8 x 6.8 KAF-4301E 2084 x 2084 24.0 x 24.0 KAF-6303E(/02LE) 3088 x 2056 9.0 x 9.0 KAF-16801E(/LE) 4096 x 4096 9.0 x 9.0

  39. Landsat 7 Orbit

  40. Landsat ETM+

  41. Landsat TM Optical System

  42. SPOT

  43. SPOT vs LANDSAT

  44. Analysis TechniquesColor Combinations

  45. Analysis TechniquesColor Combinations

  46. ASTER Parameters

  47. ASTER DATA OF CUPRITE, NV

  48. ASTER Color Combinations 1 - 2 - 3 1 - 3 - 6

  49. Analysis TechniquesRatio Images • Ratio images are formed by dividing the data value in one band by that of another band • Ratio images are used to emphasize differences in spectral reflectance of materials. For example, vegetation shows a maximum reflectance in TM Band 4 and a lower reflectance in band 2. The ratio image 4/2 enhances the vegetation signature • Ratio images minimize the difference in illumination conditions, and suppress the effects of topography • A disadvantage is that ratio images suppress differences in albedo; materials with different albedos but similar spectral properties may not be distinguishable in ratio images • Another disadvantage is that noise is emphasized in ratio images

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