2009-10 CEGEG046 / GEOG3051 Principles & Practice of Remote Sensing (PPRS) 7: sc

2009-10 CEGEG046 / GEOG3051 Principles & Practice of Remote Sensing (PPRS) 7: sc www.phwiki.com

2009-10 CEGEG046 / GEOG3051 Principles & Practice of Remote Sensing (PPRS) 7: sc

Lewis, Bob, Contributing Editor has reference to this Academic Journal, PHwiki organized this Journal 2009-10 CEGEG046 / GEOG3051 Principles & Practice of Remote Sensing (PPRS) 7: scanning redux, photography, lidar Dr. Mathias (Mat) Disney UCL Geography Office: 113, Pearson Building Tel: 7670 0592 Email: mdisney@ucl.geog.ac.uk www.geog.ucl.ac.uk/~mdisney Last week storage/transmission pre-processing stages (raw data to products) sensor scanning mechanisms This week scanning mechanisms redux photography time-resolved signals (e.g. LiDAR) Recap Scanning mechanisms: examples From: http://ceos.cnes.fr:8100/cdrom/ceos1/irsd/pages/datacq4.htm & Jensen (2000) Discrete detectors in addition to scanning mirrors L in addition to sat MSS, TM, ETM+, NOAA GOES, AVHRR, ATSR Multispectral linear arrays SPOT (1-3) HRV, HRVIR & SPOT-VGT, IKONOS, ASTER & MISR (both on board NASA Terra) Imaging spectrometers using linear in addition to area arrays AVIRIS, CASI, MODIS (on NASA Terra in addition to Aqua)

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Scanning mechanisms: examples Scanning mechanisms: continued Image frame created by scanning detector footprint n pixels per line, pixel size r r Along track speed v ms-1 so footprint travels distance r in r/v secs One line of data must be acquired in <= r/v secs Typical v Orbital period T ~ 100 mins, Earth radius ~ 6.4x103m v = 26.4x103 / 10060 = 6.7x103ms-1 Scanning mechanisms: single detector Even if we obtain 1 line in r/v secs say Significant along-track displacement from start to end of x-track scan line Scanning mechanisms: single detector Zig-zag mechanism active scan lasts r/2v secs n pixels per line, so “dwell time” (seconds per pixel) is r/2nv secs/pixel ok as long as low res e.g. AVHRR, as large r But problems as long as mod - high res. E.g. L in addition to sat MSS, r = 70m, v = 7x103ms-1 n=3000 so dwell time = 70/230007x103 = 1.7secs (OK as long as SNR) BUT with single detector, required length of scan cycle r/v is 10msecs (70/7x103) = 100 scan cycles per second TOO FAST! Scanning mechanisms: e.g. MSS MSS has 4x6 array of receptors - 4 b in addition to s, 6 receptors per b in addition to 6 lines scanned simultaneously ‘footprint’ of single receptor follows a zig-zag track ~30 cycles per second Scanning mechanisms: boustrophedon Alternative right left, left right 2 n line pixels scanned in r/v secs r/2nv secs/pixel For TM as long as e.g. r = 30m v = (20/3) x 103ms-1 n = 6000 dwell time 0.38 sec (not long enough as long as good SNR) scan cycle ~4.5 msecs (~220 per second) Way too fast i.e. single detector operation inadequate as long as TM use 6 detectors per b in addition to (vis), in addition to 16 lines at a time in vis, 4 at a time in thermal 100 detectors total From: http://rst.gsfc.nasa.gov/Intro/Part2-20.html Photography Largely obsolete due to electromechanical sensors Still used as long as some mapping in addition to monitoring applications partic. aerial surveys in addition to photogrammetry BUT requirement to get film back in addition to process it Pan-chromatic (B&W) in addition to colour (vis in addition to some IR) but limited spectrally Radial image distortion away from focal point Relatively easy to correct if camera geometry known Photography E.g. Wild RC10 aerial camera + tracker software as used by NERC Airborne Research in addition to Survey Facility www.nerc.ac.uk/arsf Software allows pilot to gauge coverage in addition to overlap Photography AP of Barton Bendish, Norfolk Acquired 1997 by NERC aircraft Scan of original Note flight info in addition to fiducial marks @ corners Photography: parameters Photographic camera uses whole-frame image capture near instantaneous snapshot of projected field-of view on ground i.e. IFOV == whole FOV Imaged region (A) focused by lens/mirror system onto focal plane (C) Spectral sensitivity from 0.3 to 0.9m i.e. Uv/vis/NIR From: http://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/chapter2/chapter2-7-e.html Photography: parameters From:http://webchat.chatsystems.com/~doswell/Outdoor-Images/Photo-Basics.html Large in addition to small apertures in camera system aperture compared to diameter of lens Photography: parameters From:http://webchat.chatsystems.com/~doswell/Outdoor-Images/Photo-Basics.html Focal length of photographic system pros in addition to cons Amount of light v. depth of field Optical mechanisms: e.g. MSS MSS optical system uses reflecting (Cassegrain) telescope Lens with hole in centre (concave) Convex focusing mirror Photography: parameters Normally adjust 4 parameters focus - by altering position of focusing lens relative to focal plane F-stop (f-number), defined as f/d i.e. Focal length / effective diameter of lens opening Shutter speed e.g. 1/2000, 1/1000, 1/500 . 1/2, 1/1, 2/1, 4/1 seconds Faster shutter = less motion blur, but less light Film “speed” - exposure level over which film responds (ISO/ASA number) Faster film responds to lower light BUT poorer spatial resolution ISO 25-100 (slow), 200-1000 (faster) Photography: parameters General film exposure equation E = exposure in Joules (J) mm-2, s = intrinsic scene brightness, in J mm-2s-1, d = diameter of lens opening in mm, t = time in seconds, f = lens focal length, mm So E is measure of recorded energy E increases with d2 , s in addition to t E decreases with f2 Note that any lens system diffraction limited i.e. can’t resolve objects smaller than s/D s = distance of object from object-side focal point; D = demagnification (Altitude/focal length i.e. D = 1/magnification = 1/s/f = f/s) Photography Historical archives of photography many military applications now declassified e.g. Surveillance (U2, Cuba, Bay of Pigs ) Vietnam, N. Korea etc. etc. From: Dr. S. Lewis, PhD thesis, 2003 UCL. Time-resolved signals: LIDAR Light Detection And Ranging optical wavelength analogue of RADAR active remote sensing used as long as laser altimetry (height measurement) but also other in as long as mation Why use optical Velocity of light ~ 3x108 ms-1 one light year = 9.46 × 1015 m (10 trillion m) used as long as cosmological distances BUT also useful as long as smaller distances Light travels ~ 30cm in 1 nanosecond (10-9s) Time-resolved signals: LIDAR So as long as LIDAR range of target from sensor ( in addition to source) is time of round trip as long as a pulse of light return pulse very weak (function of surface reflectance) & (usually) spread out LIDAR laser light from source (coherent - narrow range of wavelengths) - typically 670-700nm Spreads out as it is a wave (e.g. 10 to 100m spots on surface) Roughness variation within spot (IFOV) mean energy returns sooner from some bits than others Needs short, powerful laser pulses safety From: http://earthobservatory.nasa.gov/Library/VCL/VCL-2.html LIDAR missions SLICER Scanning Lidar Imager of Canopies by Echo Recovery http://denali.gsfc.nasa.gov/research/laser/slicer/slicer.html MOLA Mars Orbital LIDAR altimeter on Mars Global Surveyor V. Accurate info on Martian topography Clues to geological as long as mation GLAS Geoscience Laser Altimeter System on IceSAT Altimetry uses only first in addition to last return signal ICESat (aka: Laser Altimetry Mision) The Ice, Cloud, in addition to Elevation Satellite Geoscience Laser Altimeter System (GLAS) - sole instrument Combinination surface lidar with dual wavelength cloud in addition to aerosol lidar Images in addition to info from http://icesat.gsfc.nasa.gov/ Launched Jan 12, 2003 Jan 15, 2003 Earth pointing Measures ice sheet elevations changes in elevation through time height profiles of clouds in addition to aerosols l in addition to elevations vegetation cover approximate sea-ice thickness. Wave as long as m LIDAR If we can resolve more than just first/last return record shape of returning wave as long as m Wave as long as m LIDAR Contains in as long as mation about e.g. Vegetation canopy structure Requires v. accurate timing in as long as mation Again, typically green or red From:http://denali.gsfc.nasa.gov/research/laser/slicer/slicer.html Lewis, Bob InfoWorld Contributing Editor www.phwiki.com

Simulating LIDAR LIDAR – light detection in addition to ranging – optical equivalent of RADAR First/last return LIDAR Full wave as long as m more in as long as mation BUT hard to interpret So use 3D models to simulate & underst in addition to New (ish) measurements: LIDAR Harwood as long as est, Northumberl in addition to , UK. 2003 In as long as mation Canopy height Canopy gap fraction in addition to vertical profile of foliage Structural in as long as mation from LIDAR Possibly in situ laser scanning E.g. First/last return LIDAR data

Lidar signal: single birch tree Allows interpretation of signal, development of new methods Disney et al. (2009) IEEE TGRSS, 47(10), 3262-3271 Lidar signal: single conifer tree, materials Allows interpretation of signal, development of new methods Disney et al. (2009) IEEE TGRSS, 47(10), 3262-3271 E.g. Wave as long as m LIDAR data Canopy height AND density in as long as mation intensity of return related to density from http://ltpwww.gsfc.nasa.gov/eib/projects/airborne-lidar/slicer.html

Orbital period T of satellite (in s) = 2/ (remember 2 = one full rotation, 360°, in radians) in addition to RsE = RE + h where RE = 6.38×106 m So now T = 2[(RE+h)3/GME]1/2 Example: geostationary altitude T = Rearranging: h = [(GME /42)T2 ]1/3 – RE So h = [(6.67×10-115.983×1024 /42)(246060)2 ]1/3 – 6.38×106 h = 42.2×106 – 6.38×106 = 35.8km Orbits: examples Example: polar orbiter period, if h = 705x103m T = 2[(6.38×106 +705×103)3 / (6.67×10-115.983×1024)]1/2 T = 5930.6s = 98.8mins Example: show separation of successive ground tracks ~3000km Earth angular rotation = 2/246060 = 7.27×10-5 rads s-1 So in 98.8 mins, point on surface moves 98.8607.27×10-5 = .431 rads Remember l =r as long as arc of circle radius r & in radians So l = (Earth radius + sat. altitude) = (6.38×106 +705×103) 0.431 = 3054km Orbits: examples

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