CEE 6100 / CSS 6600 Remote Sensing Fundamentals 1 PHOTOGRAMMETRY DEFINITION (adapted from Manual of Photographic Interpretation, 2 nd edition, Warren Philipson, 1997) Photogrammetry and Remote Sensing: The art, science, and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting imagery and digital representations of energy patterns derived from non-contact sensor systems. 1) metric photogrammetry: making precise measurements from photos. 2) interpretative photogrammetry: recognizing and identifying objects and judging their significance through careful and systematic analysis. See also: Elements of Photogrammetry with Applications in GIS (2014) Paul R. Wolf, Bon A. Dewitt and Benjamin E. Wilkinson. McGraw-Hill Education, 4th edition, ISBN: 9780071761123 Photogrammetry: Making precise measurements from images Close range photogrammetry: with camera focus set to a finite value. Far range photogrammetry: with camera focus set to infinity Basic Optics: thin lens equation: 1 + 1 = 1 oo ii ff magnification: MM = ii = h oo h = iiiiiiiiii ssssssss oooooooooooo ssssssss depth of field object h o θ f i h' image Long range photogrammetry: focus at infinity thin lens equation: 11 + 11 ii = 11 ff oo oo ii ii ff (oo ) magnification: MM = h h = imagesize oooooooooooosize = ff oo = SSSSSSSSSS o i f
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 2 Horizontal resolution and Scale Resolution will depend on: inherent resolution of the film or spacing of detectors in a digital array depth of field (circle of confusion) characteristics of the optics lens quality focal length imaging geometry d optic axis D FOV f = focal length H = altitude Uniformity of Scale 1. Photo taken with film plane at an angle to the building face. Note that the roof line and ground line are not parallel. (variable scale) 2. Photo taken with film plane parallel to the building face. Note that the roof line and ground line are parallel. (uniform scale) 3. Photo of the left end of building taken with film plane parallel to the building face. Distance from the building is approximately the same as in photo 2. 4. Composite of photos 2 & 3
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 3 Scale H f digital array (or aerial film) S = f / H rear nodal point front nodal point reduced print contact print enlarged print datum plane Scale = image distance/ground distance 1:24,000 1" = 2,000 ft. small scale 1:250,000 1 mm = 24,000 mm large scale 1:12,000 Resolution The resolution of the system is the measure of how close a pair of lines can be to one another and still be distinguished. The smallest separation, d, of a pair of bars that can be distinguished by an imaging system defines its resolution. The spatial resolution of a digital frame camera will depend on the spacing of the elements in the detector array. The closer the spacing, the higher the resolution will be for a given lens system and focal length. For film the resolution depends on the size of the grains of the silver salts that form the image: the smaller the grain size, the higher the spatial resolution of the film and the slower the film speed. The highest spatial resolutions available for aerial photographic films are typically 200 lp mm -1. This corresponds to a typical grain size of ~1 µm. The detector spacing for a comparable digital frame camera would be ~5-10 µm. Resolution Test Patterns Sector Star Target (for astigmatism). Each test target comes with a chart that specifies the line pairs per mm (l ppm) for each group and element The aerial version is in line pairs per meter. 30 22.140'N, 89 33.959'W 30 23.161'N, 89 37.733'W
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 4 Components of a film mapping camera Lens Assembly: The lenses of aerial systems are multiple-lens systems with a betweenlens field stop and shutter. The focus is fixed at infinity. Typical focal lengths are 3.5, 6, 8.25 and 12 inches. Focal Plane: This is a plate aligned perpendicular to the optical axis of the lens. A vacuum system is used to fix the film to the plate so the focal plane is perfectly flat during exposure. Lens Cone: Holds the lens and filter, and covers the front part of the camera preventing light from leaking into the camera body. Body: Encloses the camera, the mounting bolts and stabilization mechanism. Drive Assembly: The winding mechanism, shutter trigger, the vacuum pressure system and motion compensation. Magazine: Holds the roll of unexposed film, advances the film between exposures, holds the film in place and winds-up the exposed film. Magazines may be exchanged in-flight. Focal length: The distance between the rear (emergent) nodal point and the focal plane. Equivalent focal length: The distance along the optical axis to the plane of best average definition (measured). Calibrated focal length: an adjusted value of the equivalent focal length, computed such that the effect of lens distortion is distributed over the entire field. RMK TOP - Aerial Survey Camera System CAMERA TOP RMK TOP 15 focal length 153 mm (6 "), angular field 93 (diagonal), aperture f/4 to f/22 continuously, distortion <= 3µm RMK TOP 30 focal length 305 mm (12") angular field 56 (diagonal), aperture f/5.6 to f/22 continuously, distortion <= 3µm SUSPENSION MOUNTT-TL (gyro-stabilization suspension mount) Stabilization range: ± 5 in omega, ± 5 in phi, ± 6.5 in kappa max. angular speed: 10 /s max. angular acceleration: 20 /s²
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 5 Intergraph DMC II250 Specifications 4 high-resolution 14K x 17K panchromatic cameras Final output image: 14,656 x 17,2164 pixels Field of view: 46.6 cross track x 40.2 along track Lens system: 4: x f = 120mm/f:4.0 Four multispectral 7K x 8.5K cameras: red, green, blue, and near infrared Spectral sensitivity: Blue: 400-580 nm; Green: 500-650 nm; Red: 590-675 nm; NIR: 675-850 nm; NIR alternate: 740-850 nm. Custom filters available upon request Lens system: 4: x f = 25mm/f:4.0 Shutters and f-stop: continuously variable 1/50-1/300 sec, f/4-f/22 On-board storage capacity: 1.5 TB (1350 images) Maximum frame rate: 1.7 sec/image Radiometric resolution: 14 bit (all cameras) Ground pixel size: 2.5 cm @ 500 m Forward Motion Compensation (FMC) +y y-fiducial axis fiducial marks x-fiducial axis -x +x photographic center (principal point) -y fiducial ma Airphoto Hidalgo County, TX http://www.colorado.edu/geography/gcraf t/notes/remote/gif/hidalgo.jpg
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 6 Scale change with topography PHOTO f ELEVATION b b' a' a Above datum = H Above A: H A' = H - h A Above B: H B' = H - h B S = f/(h - h) H B h B GROUND A A' B' h A DATUM Relief displacement nadir point photo t b a b' a' r b' d r a b ra' r t ra f d a = r a h A H H h T h B datum R B ground R A A A' h A Near-vertical kite aerial photograph. Notice different view of trees near scene center in comparison to trees at far right. Cucharas Pass, Colorado; photo date 6/00, J.S. Aber. Source: http://academic.emporia.edu/aberjame/airphoto/p_gram/p_gram.htm
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 7 Source: http://www.photoscience.com/airphoto.htm#sample Air Photo Tilted Aerial Photograph Tilt displacement A point that would have been imaged at a' on a vertical photo is actually imaged at a on the "up side" of the tilted photo. The tilt displacement of points on the "up side" of the tilted photo is then toward the isocenter while points on the "down side" are displaced away from it.
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 8 Tilt displacement is always relative to the isocenter. Scale change is in the direction of tilt. The nadir point is always on the down side of the axis of tilt and opposite the principal point from the isocenter Equivalent vertical photo d' d d'' B f t n' i n perspective center A f P a a'' tilted photo a' The direction of tilt displacement is radial relative to the isocenter. The amount of displacement is proportional to the distance from the isometric parallel. Oblique photography: Extreme tilt displacement Image areas on the upper side of the tilt are displaced further away from the ground than is the isocenter and are at smaller scales than the nominal scale. Image areas on the lower side of the tilt are displaced closer to the ground than the isocenter and are at larger scales than the nominal scale. Source: http://www.aboveallphoto.com/oblique_photography.html
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 9 isometric "up side" e e'' d d'' n i p c, c'' isometric parallel principal line a I b a'' b'' 2, 1 p i n 2 1 3 "down 1 side" 2 3 1 3 2 principal 3 1 2 Relief & Tilt displacement 1. Location of an object on the datum plane for an untilted photo 2. Position of the object on a vertical photo due to relief displacement. (Object is above the datum plane.) 3. Position of the object on a tilted photo due to tilt displacement. Stereo Air-photo terminology Principal point: Geometric center of photograph. Literally the point on the ground in line with axis of camera lens. Fiducial marks: Marks on the photograph margins used to locate principal point in photo. Conjugate principal point: Point in overlapping photo that is equivalent to principal point of adjacent photograph. Photo base: Distance between principal point and conjugate principal point measured on a single photograph. air base 1 2 n1 a n2 n n2' b' a' 1' elevation H above datum Ground (air) base: Ground (air) distance between principal points of overlapping photographs. Parallax: Apparent shift in relative positions of objects when viewed (photographed) from different vantage points. N b A 1 DATUM N 2 B
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 10 Stereo Imagery from a frame camera Determining height from stereo imagery Determining the height of the Washington Monument using stereo parallax 555 ft 5.9 in (169.314 m) Stereo Imagery from Mars http://mars.jpl.nasa.gov/mpf/mpf/stereo-arc.html
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 11 Height Measurement dp 1 dp 2 flight path O 1 O 2 O 1 O 2 x' 1 x' 2 X 1 X 2 O 1, O 2 = nadir points of photo 1 and photo 2, respectively X 1, X 2 = location of the base of the tree x' 1, x' 2 = position of the base of the tree along the flight path dp 1, dp 2 = relative parallax Change in height dp1 dp2 rear node (lens) f o1 x1 o2 o1 x2 o2 image plane H-h H h O1 dp2 dp1 O2 dp P = absolute parallax parallax difference: dp = dp1 dp2
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 12 Flight Planning Factors to consider: 1. General issues focal length array/film size (format) scale / FOV overlap / sidelap (continuous coverage, stereo, ) 2. Issues specific to the application spectral considerations (film / filter) time of day (illumination, sun orientation, tidal stage, ) season (crop calendar, leaf on, leaf off, ) sun orientation, sun angle Focal length The nominal scale of the photo is the ratio of the focal length to the altitude: scale = f / altitude If the image medium can resolve 1 line pair / d, the equivalent ground resolution is: r gnd = d / scale The FOV of the image is related to the film/array format. (e.g., film format: 23 cm (9"); array format: 100 x 57 mm) FFFFFF = ffffffffffff ssssssssss Vertical resolution, a function of the distance between images, the altitude and the film resolution, may be estimated as: aaaaaaaaaaaaaaaa rr gggggg rr hhhhhh = dddddddddddddddd bbbbbbbbbbbbbb nnnnnnnnnn pppppppppppp rr gggggg Overlap Plan for 60% overlap (endlap), especially for stereo flights. Can be less if stereo is not required 1 2 3 4 5 6 7 8 consecutive frames collected by camera at equal time intervals endlap coverage of a single photo 1 2 3 4 5 6 7 8 photo centers nadir line (ground flight path) photos aligned to fit a base map horizontal shift and rotation due to drift and correction for crabbing
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 13 Sidelap Plan for 30% overlap (sidelap) in order to insure complete coverage (no gaps). flight path Sources of Aerial Photography USGS National Aerial Photography Program: https://lta.cr.usgs.gov/napp Standardized images, cloud-free, every 5-7 years Collected at 20,000 ft; about 1 m resolution Centered on one-quarter section of a 7.5-minute USGS quadrangle, and covers approximately a 5.5 x 5.5 mile area USDA Aerial Photography Field Office https://www.fsa.usda.gov/programs-and-services/aerial-photography/ Imagery dated beginning with 1955 to the present at this site. Imagery prior to 1955 are held by the National Archives but must be ordered. More information here. National Oceanic and Atmospheric Administration (NOAA) Coastal Aerial Photography https://data.noaa.gov/dataset National Air Photo Library (NAPL) of Canada http://www.nrcan.gc.ca/earth-sciences/geomatics/satellite-imagery-air-photos/9265 Commercial sources: http://www.geomart.com/products/aerial/index.htm State agencies
CEE 6100 / CSS 6600 Remote Sensing Fundamentals 14 Spectral Considerations What spectral bands will highlight the target in the expected background? vegetation: NIR/Red is characteristic of vegetation mineral exploration: Specific band selection will depend on the minerals in question, but most will be in the Mid-IR or SWIR. water quality: visible channels will dominate. Seasonal Considerations Will the target be more detectable at some times of year? vegetation: discrimination between oak and maple may be most effective in early spring when maple has leafed out but oak has not. mineral exploration: any season will do if there is no cloud cover (or snow). water quality: - wet season vs. dry season - temperature regime (thermocline, plankton growth) - seasonal land use changes (tourism, industry, recreation) Time of day considerations Will the target be more detectable at certain times of day? vegetation: discrimination between oak and maple may be most effective in early spring when maple has leafed out but oak has not. mineral exploration: shadows may be an advantage (low sun angle) in some cases. water quality: - tidal stage - relatively high sun angle (to maximize the amount of light entering the water). Flight alignment Flight lines are usually planned to be parallel to each other and parallel to the long axis of the study area. (Minimizes aircraft turns which are very time consuming.) Complicating factors: wind (causes the aircraft to crab or drift across the flight path). topography (low altitude flights in mountainous areas may result in flight lines that are not parallel to the long axis of the study area. restricted zones (airports, military bases), national borders, Issues specific to line scanning systems sun angle effects (BRDF) may be minimized by selecting a flight line into or out of the sun.