GIS 255 Final

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GIS 255 Final
2011-12-12 00:50:29
Remote Sensing final exam

Notes for the final exam in GIS 255.
Show Answers:

  1. What 4 things should a vegetation index do?
    • 1. Maximize sensitivitiy to plant biophysical parameters
    • 2. Normalize or model external effects such as sun angle, viewing angle, and the atmosphere
    • 3. Normalize internal effects such as canopy background variations, soil variations, and differences in senesced vegetation.
    • 4. Be coupled to a specific measureable biophysical parameter
  2. How to differentiate snow from clouds in a Landsat 7 ETM+ image using a band ratio or index?
    ETM Band 5 / (ETM Band 1 + ETM Band 2 + ETM Band 3), because Band 5 has low reflectivity for snow but high reflectivity for clouds.
  3. Which ETM+ band is absorbed the least by water?
    Band 1.
  4. Describe how atmospheric effects can
    a. affect a change detection routine and
    b. how to compensate for those effects
    Different atmospheric constituents (gases, aerosols, and clouds) can causes unwanted path radiance at the sensor which can show up as change when no change has occurred. Compensation may be as simple as converting to reflectance before change detection or as complicated as running atmospheric correction routines to eliminate/reduce the effects of the atmosphere.
  5. Which Landsat TM processing level is the best to use for change detection and why: L1T, L1R, L1Gt?
    L1T because it has the highest geodetic accuracy, utilizing GCPs and a DEM. L1Gt only uses a DEM and L1R has no geometric correction applied.
  6. Why perform histogram matching before attempting change detection?
    Histogram matching increases the contrast of the images, allowing for a more effective difference image.
  7. In the remote sensing system, what is Path 4?
    Radiation that was reflected by nearby terrain (p lambda) covered by snow, water, concrete, vegetation, etc. into the IFOV.
  8. What paths is path radiance made of?
    Path 2 and Path 4; generally to be avoided.
  9. What is target radiance?
    Paths 1, 3, and 5; generally valuable.
  10. What is radiance path 5?
    Radiance that was reflected by nearby terrain into the atmosphere before being reflected back into the nearby study area.
  11. Why must cross-calibration methodologies consider adjustments for differences in illumination and observation angles?
    Because images from 2 different platforms are calibrated and compared againts each other and those images are never captured with exactly identical configurations and the processing of the images must compensate for the differences in illumination and observation angles.
  12. How does the Landsat TM cross-calibration adjust for differences in illumination and observation angles?
    Because data acquisitions were only 10 to 30 minutes apart during the tandem configuration period, it is assumed that the surface and atmospheric conditions did not change significantly between the two image acquisitions. For Landsat sensor image data pairs acquired during the tandem configuration period, the expectation is that such adjustments are not necessary.
  13. What is the Landsat Data Level product L0R?
    • It provides reformatted raw data with no geometric or radiometric correction applied. Reformatting includes shifting pixels by integer amounts to account for
    • -The alternating forward-reverse scanning pattern of the sensor;
    • -The odd-even detector arrangement within each band, and
    • -The detector offsets inherent to the focal plane array engineering design.
  14. What is radiance path 3?
    Energy from the Sun that has undergone some scattering and perhaps some absorption or reemission before illuminating the study area.
  15. What is the Landsat Data Level product L1T?
    It provides systematic radiometric accuracy, geometric accuracy by incorporating ground control points, while also employing a digital elevation model (DEM) for topographic accuracy. Geodetic accuracy of the product depends on the accuracy of the ground-control points and the resolution of the DEM used.
  16. What color is healthy vegetation in a CIR composite?
  17. Total path radiance at the sensor (Ls) is composed of what two radiances?
    Lt and Lp
  18. When does Rayleigh scattering occur?
    When the diameter of the air (or whatever) molecules is many times smaller than the wavelength of the incident electromagnetic radiation.
  19. When does Mie scattering occur?
    When the molecules are essentially spherical and w/diameters approximately equal to the length of the incoming wavelengths.
  20. What must one do to convert total radiance at the sensor (Ls) into a physical property of the target?
    Convert to reflectance.
  21. What is the Landsat Data Level product L1G?
    It provides systematic geometric and radiometric accuracy, which is derived from data collected by the sensor and spacecraft. The scene will be rotated, aligned, and georeferenced to a user-specified map projection. Geometric accuracy of the systematically-corrected product should be within 250m for low-relief areas at sea level.
  22. Why convert radiance data into reflectance data?
    For relatively clear Landsat scenes, a reduction in between-scene variability can be achievedthrough a normalization for solar irradiance by converting spectral radiance, as calculatedabove, to planetary reflectance or albedo.
  23. What is radiance path 2?
    Spectral diffuse sky irradiance (Ed) that never reaches the target b/c of scattering in the atmosphere.
  24. What is the Landsat Data Level product L1Gt?
    It provides systematic radiometric and geometric accuracy, while using a DEM for topographic accuracy. The latter depends on the resolution of the DEM used.
  25. Which classification algorithms are parametric?
    Maximum likelihood, minimum distance/nearest mean, Mahalanobis.
  26. Which are nonparametric classification algorithms?
    K-means, ISODATA, parallelepiped.
  27. In remote sensing, by what Greek letter is the set of angles tht describe the relationsip between the source, the target, and the sensor referred?
  28. What kinds of pre-launch calibration are there?
    • 1. Spectral characterization
    • 2. Radiometric calibration
    • 3. Spherical integrating source
  29. What kinds of post-launch calibration are there?
    • 1. Internal calibrator.
    • 2. Full-aperture solar C.
    • 3. Partial-aperture solar C.
  30. What is Level 1R?
    Radiometrically corrected.
  31. What is level 1G?
    Radiometrically and geometrically corrected.
  32. What is level 1T?
  33. What are the elements of image interpretation?
    • Tone
    • Texture
    • Pattern
    • Shape
    • Size
    • Association
  34. What does NIIRS stand for?
    National Image Interpretability Ratings
  35. How many NIIRS levels are there?
    10 (from 0 to 9)
  36. What does NDVI equal to?
    (reflectance NIR - reflectance red)/(reflectance NIR + reflectance red)
  37. What is a parametric classification algorithm?
    One that assumes a particular class statistical distribution (e.g., normal) for classification.
  38. What is a nonparametric classification algorithm?
    One that makes no assumptions about probability distributions.
  39. Are K-Means and ISODATA supervised or unsupervised classification methods?
    Unsupervised (requiring no input from the user to cluster pixels in a dataset, but based on statistics only).
  40. Are parallelepiped, maximum likelihood, minimum distance, and Mahalanobis distance supervised or unsupervised classification algorithms?
  41. At what NIIRS level should one be able to detect a medium-sized port facility?
    Level 1.
  42. At what NIIRS level should one be able to distinguish between natural tree stands and orchards?
    Level 3.
  43. At what NIIRS level should one be able to detect open bay doors of vehicle storage buildings and classify locomotives by type?
    Level 5.
  44. Should one be able to see individual railroad ties at NIIRS 7?
  45. At multispectral IIRS level 1, should one be able to distinguish between urban and rural areas?
  46. At what IIRS level should one be able to detect small boats in open water?
    Level 4.
  47. At what IIRS level should one be able to identify individual 55-gallon drums?
    Level 7.
  48. Where is chlorophyll a peak absorption?
    Between 0.43 and 0.66 micrometers.
  49. Where is chlorophyll b peak absorption?
    Between 0.45 and 0.65 micrometers.
  50. Describe the tasseled-cap distribution.
    The x-axis is red reflectance, the y-axis is near-infrared reflectance; the "tassel" is high canopy closure or biomass, the left corner is wet bare soil, the right corner (somewhat above the former) is dry bare soil.
  51. What is the simple ratio vegetation index?
    Reflectance NIR/Reflectance red
  52. Over water, what is Lt made up of?
    • Lp (atmospheric path reflectance, never touches the surface)
    • Ls (free-surface layer reflectance, bounces off the surface)
    • Lv (subsurface volumetric reflectance, reflected off some point below the surface)
    • Lb (bottom reflectance)
  53. What is the ultraviolet portion of the spectrum?
    Below 400 nm.
  54. Where is absorption in pure water?
    Ultraviolet (<400 nm) and yellow through near-infrared (>580 nm) portions of the spectrum.
  55. What is the best wavelength region for discriminating land from pure water?
    Near-infrared and middle-infrared (740-2500 nm)
  56. The more sediments are there in water, the more the reflectance peak shifts toward _____________ _____________.
    longer wavelengths.
  57. Where is the reflectance of snow in the 0.4 - 2.5 micrometer interval?
    Below 1.5
  58. How does the reflectance of clouds compare to the reflectance of clouds in the 0.4-2.5 micrometer interval?
    Approximately same as snow below 1.5, slightly less but still almost the same above.
  59. What is uninteresting change?
    • 1. Phenological change
    • 2. Sun angle effects
    • 3. Atmospheric effects
    • 3. Geometric effects

    Can be dealt with by radiometric calibration, anniversary-date acquisition, and highly accurate registration.