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RS midterm
remote sensing midterm
| Question | Answer |
|---|---|
| What is the definition of RS? | • measuring environmental variables or EM radiation without direct contact with the target • use of math + statistics based algorithms to extract valuable info from RS data |
| What technological components make photography possible? | 1. light + color theory: light is made up of all colors; IR + UV radiation have effects without being visible 2. a recording instrument: first example was pinhole photography through the camera obscura |
| What are the advantages of RS? | 1. does not disturb target when observed passively 2. can be programmed to collect data systematically, eliminating sampling bias 3. fundamental biophysical info under controlled conditions 4. accurate, cheap, frequently updated |
| What are the disadvantages of RS? | 1. often oversold; cannot provide all the info for research 2. human error may be introduced when specifying instrument + mission parameters 3. always needs validation from other sources |
| What are passive RS systems? | • systems that record naturally occurring EM radiation reflected or emitted from the terrain; ex. photography, multispectral scanning |
| What are active RS systems? | • systems that supply energy to illuminate the scene then record radiant flux scattered back to the sensor; ex. microwave (radar), laser sensors |
| What are the seven steps of the general RS process? | 1. energy source / illumination 2. radiation + atmosphere 3. interaction with target 4. sensor records energy 5. transmission, reception, processing 6. interpretation + analysis 7. application |
| What are the four resolutions of RS data? | 1. spatial: size of FOV; ex. 10x10 m 2. spectral: bands that the sensor records; ex. thermal IR 3. temporal: how often sensor records data; ex. every 30 days 4. radiometric: sensitivity of detectors; ex. 16-bit |
| What is analog imagery? | • hard-copy aerial photography / video data; cannot be processed after development • mathematically represented as range of values representing position + intensity |
| What is a pixel? | • smallest picture element in an image, assigned a value + location |
| What is IFOV? | • instantaneous field of view; ground area viewed by a sensor at a given instant |
| Major RS softwares: | 1. ERDAS Imagine 2. ENVI/IDL 3. PCI EASY/PACE 4. ER Mapper 5. ARC/INFO GRID 6. ESRI ArcView (ArcGIS) Image Analyst |
| Major RS journals: | 1. RS of Environment 2. ISPRS Journal of Photogrammetry + RS 3. Photogrammetric Engineering + RS 4. Geocarto International |
| What is the relationship between energy source and illumination? | • the Sun is the original energy source for Earth, and it provides illumination • incoming solar radiation may be reflected or absorbed by clouds, Earth's surface, water vapor, dust, ozone, etc. |
| What are EM waves and how do they travel? | • EM waves are transverse waves made by vibrating electric charges • they travel through space as electric + magnetic fields both perpendicular to the wave's direction |
| What are the types of EM radiation? | • radio, microwave, infrared, visible (red --> violet), ultraviolet, x-ray, gamma rays |
| What are the three types of energy transfer? | 1. conduction: heat transfer through direct contact 2. convection: heat transfer through circulating fluids (liquids + gases) 3. radiation: energy transfer through EM waves |
| Describe refraction: | • bending of light when it passes from one medium to another of a different density • measure of a substance's optical density |
| Describe scattering: | • reflection of EM energy by atmospheric particles • does not affect wavelength or intensity |
| Describe absorption: | • when radiant energy is absorbed + converted into other energy forms |
| Describe reflection: | • when radiant energy "bounces" off a surface • specular reflection: smooth surface, waves remain parallel • diffuse reflection: rough surface, waves reflect in many directions |
| What is Raleigh scattering? | • occurs 2-8 km high in the atmosphere, where particle diameter is much smaller than EM wavelength • blue skies: radiation with shorter wavelength (blue + purple) scatters more easily |
| What is Mie scattering? | • occurs ~4 km high in the atmosphere, where particle diameter is roughly equal to EM wavelength • pollen, dust, smoke, water, etc. |
| What is nonselective scattering? | • occurs where particle diameter is larger than EM wavelength • all wavelengths scattered equally --> haze effect, reduced spatial detail + image contrast |
| What are atmospheric windows, and what is their use? | • regions of the EM spectrum that pass through Earth's atmosphere with little absorption or scattering • different windows allow for the use of specific sensors operating at those ranges |
| What are the three terrain energy-matter interactions? | 1. reflection: bounces off terrain 2. absorption: absorbed by terrain 3. transmission: travels through terrain • R + A + T = 100% |
| What energy-matter interactions are introduced at the sensor, and what errors are associated with those? | • ideally: recorded radiance is true measure of that leaving target terrain within IFOV at specific angle • other radiation can enter IFOV and cause noise • different radiation interacts uniquely with materials in film cameras + sensors |
| What is a vantage point? | • a position / standpoint from which a target is viewed / considered |
| What is a filter? | • a material that selectively absorbs some wavelengths of light reflected from the target while letting the rest of the light through to the camera |
| What is a polarized filter? | • a filter that absorbs sunlight incoming to the sensor from specific angles |
| What is film? | • light-sensitive layer reacts to form image when exposed to light; must be developed • light-sensitive emulsion layer, supportive base material, anti-halation layer (prevent reflection back through emulsion) |
| Explain the relationship between focal plane + focal length: | • plane: area where film is held flat during exposure • length: mm from lens optical center to focal point • when subject is in focus, focal point lies on the focal plane • fixed focal plane: features smaller at shorter focal length |
| Explain wide-angle cameras: | • a camera with a focal length less then 35 mm; creates a wider FOV |
| What is a vertical photograph + the associated optical axis threshold? | • vertical photos are taken directly above the target; best for mapping + measurements • camera's optical axis must be within 3 degrees away from direct vertical from target |
| What is the difference between low + high oblique photographs? | • oblique: photo taken from an angle; best for 3D perspective • low: horizon not shown in the photo • high: horizon shown in the photo |
| What are the advantages of vertical imagery? | 1. essentially constant scale 2. easy, accurate measurements 3. can be used as a map when combined with grids + marginal data 4. easier interpretation, especially stereography |
| What are the advantages of oblique imagery? | 1. much larger area covered in one photo (assuming constant sensor + altitude) 2. view may be more familiar to interpreter 3. some objects are seen that were invisible vertically |
| Describe frame cameras: | • takes a single image of a large area using an array of detectors simultaneously |
| Describe scanners: | • uses single detector to sweep across terrain, builds large image from many smaller ones |
| Describe linear arrays: | • push broom: takes long images one after the other, no rotating mirror • whisk broom: uses rotating mirror to sweep across terrain + take many small images, similar to a scanner |
| Describe hyperspectral data arrays: | • takes long images with no rotating mirror similar to push broom • captures image across many small, continuous spectral bands simultaneously to make a thick cube of data |
| What is additive color theory? | • based on mixing light; used to display images on monitors |
| What is subtractive color theory? | • based on mixing pigments; used when working with filters |
| Describe black + white film: | • panchromatic sensitive layer |
| Describe black + white infrared film: | • near-infrared sensitive layer |
| Describe normal color film: | • blue sensitive layer - yellow filter - green sensitive layer - red sensitive layer |
| Describe color-infrared film: | • near-infrared sensitive layer - green sensitive layer - red sensitive layer |
| What is the impact of time of day on aerial photography mission planning? | • affects illumination, quality, shadows, hot spots • ideal: within 2 hours of solar noon, Sun 30-52 deg above horizon • low sun angle may be preferred to enhance terrain representation |
| What is the impact of weather on aerial photography mission planning? | • affects scattering + absorption (water vapor), flight line (drift from wind), haze (smog + clouds) • ideal: few days after passage of frontal system • maybe before system if low wind + humidity |
| What is the impact of flightline layout on aerial photography mission planning? | • info needed: photo + base map scale, coordinates of study area corners, area size, forward overlap + sidelap, film + camera • calculations: altitude, # of flightlines, distance between flightlines + exposures, # of exposures |
| What is aerial photographic interpretation? | • examining images to identify objects + judge significance; visually or through computer processing • provides 3D depth perception, knowledge of non-visible spectrums, historical records + change detection |
| What are the nine elements of image interpretation? | 1. x,y location 2. tone + color 3. size 4. shape 5. texture 6. pattern 7. shadow 8. site 9. association |
| Describe the element x,y location: | • link to other contextual info |
| Describe the element tone + color: | • average brightness of an area (tone = B+W) / dominant color • specular vs. diffuse reflection |
| Describe the element size: | • dimensions of a feature, ex. length + area • relative size: compare target with surroundings • absolute size: use an aerial image to derive measurements |
| Describe the element shape: | • outline of a feature, dependent on perspective • scale effect: scale of an uncorrected overhead image is not consistent across the image |
| Describe the element texture: | • variation in tone / apparent roughness caused by shadows of terrain irregularities |
| Describe the element pattern: | • distinctive arrangement of features |
| Describe the element shadow: | • outline of an object projected onto a flat surface opposite the light source • depends on object, angle of illumination, perspective, slope of ground surface |
| Describe the element site: | • position with respect to topography, drainage, function • ex. power plants placed by water source for cooling |
| Describe the element association: | • relationships between features • ex. large parking lot - shopping mall |
| What is georeferencing? | • aligning geographic data to known coordinate system so it can be viewed + applied + analyzed with other geographical data • allows for accurate direction + distance + area measurements |
| What are the six commonly used georeferencing systems? | 1. place names 2. postal addresses + codes 3. linear referencing 4. cadastral maps 5. latitude + longitude 6. projections + coordinates |
| Explain georeferencing by place names: | • most common everyday form • names may be universally recognized, work on different scales, and may also fade with time |
| Explain georeferencing by postal addresses + codes: | • fails in rural areas, for natural features, where addresses are not sequential |
| Explain georeferencing by linear referencing: | • roads, streets, rails, rivers • measure distance from reference point, often an intersection |
| Explain georeferencing by cadastral maps: | • cadastral maps: land ownership records maintained for taxing + public record • only accessible to local officials with ID codes for each land parcel |
| Explain georeferencing by latitude + longitude: | • most comprehensive, powerful, exact • well-defined, supports other spatial analysis |
| What are latitude lines? | • parallel lines measured north + south of the Equator |
| What are longitude lines? | • parallel lines called meridians measured east + west of the Prime Meridian |
| Explain georeferencing by projections + coordinates: | • project Earth's surface onto a plane for easier measuring, but will distort dimensions in some way |
| Describe cylindrical map projections: | • conformal: preserve small-scale angles + shapes but distort overall scale of image • most well-known is Mercator: lat + long perpendicular, but high lat very enlarged; cylinder placed around equator |
| Describe conical map projections: | • lat appear as arcs of circles, long extend straight from the poles • Lambert Conformal Conic Projection: commonly used to map north America |
| Describe azimuthal / planar map projections: | • surface projected straight onto flat surface |
| What is the Universal Transverse Mercator Projection? | • cylinder placed around poles (vs. equator in original Mercator) • maps a large north-south region with low distortion • 60 zones, each 6 deg long wide, max distortion 0.04% |
| Why does RS need geometric correction? | • individual pixels must must be in their correct planimetric (x,y) locations • only geometrically correct images give accurate distance + polygon area, direction info |
| What are GCPs? | • ground control points: can be both identified in imagery + located on a map, both coordinates required for rectification • paired coordinates are modeled --> geometric transformation coefficients to rectify data |
| What are affine transformations? | • maintain relative arrangement of points + straightness of lines, not distances + angles |
| Describe first-order affine transformations: | • linear; fits plane to data to rectify uniform distortions (translation, scale, rotation) in small areas |
| Describe second-order + third-order affine transformations: | • bend + curve image to best match ground features |
| What are the basic steps of the iterative geometric correction process? | 1. use all GCPs for initial set of coefficients + constants, calculate RMSE for each GCP then sum 2. delete GCPs contributing most error 3. compute new values from remaining GCPs + repeat until below error threshold 4. use final values to rectify image |
| How is the accuracy of geometric correction evaluated? | • calculate RMSE for each GCP • algorithm + coefficients are more accurate when original x,y GCP coords are closer to computed coords |
| Describe nearest neighbor method for intensity interpolation: | • brightness value closest to predicted x,y coord is assigned to output x,y coord |
| Describe bilinear method for intensity interpolation: | • assigns output values by interpolating brightness in 4 surrounding pixels • pixels closer to desired x,y location will have more weight in final computations |
| Describe cubic convolution method for intensity interpolation: | • assigns output values by interpolating brightness, similar to bilinear method, but uses 16 surrounding pixels |
Created by:
junoreg
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