2012 ASPRS Track, Satellite Image Geometry, Gene Dial
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2012 ASPRS Track, Satellite Image Geometry, Gene Dial



A fast-paced tutorial on satellite image geometry. ...

A fast-paced tutorial on satellite image geometry.
 Mono & stereo collection geometry.
 Effects of collection geometry on image quality, perspective and accuracy.
 RPC & Physical Camera Models
 Geometry of scan-oriented, map-oriented, orthorectified, and stereo image products
This tutorial for producers and users of satellite imagery provides a common vocabulary and understanding of collection and product geometry and effects.



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  • GeoEye revenue About ½ from commercial customers About ½ from the US Government By contrast, the US Government pays 100% of cost for National Technical Means. So we're a very cost effective alternative. Congress, by supporting US commercial imagery satellite companies, is increasing American security and protecting American jobs, but only paying 50 cent dollars to do so.
  • So it’s into this historic background that GeoEye was formed by the acquisition of Space Imaging by OrbImage early in 2006. Our headquarters is conveniently located in Dulles Virginia. We’ve grown to 410 employees at various locations around the country and even around the world. We collect imagery from a constellation of satellite and aerial platforms. The listing of GeoEye stock on the NASDAQ exchange and our inclusion in the Russell 3000 speak to the evolving maturity of our industry. When the first JACIE conference was held, we concentrated on narrow, technical aspects of remote sensing. Today, we are truly an industry, blending requirements for customer service and back-office production systems with consideration of resampling kernels, MTFC, and acquisition angles.
  • GE1 = Green GE2 = Blue IL = Yellow

2012 ASPRS Track, Satellite Image Geometry, Gene Dial 2012 ASPRS Track, Satellite Image Geometry, Gene Dial Presentation Transcript

  • Satellite Image Geometry Gene Dial GIS in the Rockies 2012-09-21 1
  • Topics› Background› Satellite Orbits› Satellite Image Geometry› Stereo Image Geometry› Satellite Image Products Niagara Falls 2
  • Background
  • Remote Sensing—Then & Now!Mys Shmidta Air Field, Soviet Union GeoEye-1 Half Meter Imagery Collected August 18th, 1960 Kutztown University – Collected Oct. 6, 2008
  • GeoEye-2 Technical Specs at a GlanceSystem Specificatio Performance n Power Solar Array (5)Satellite Bus Size 2.3 m x 5.3 m Control Data Storage Unit (2) Weight 2100 kg dry, 2500 kg wet Flight UnitPayload Aperture 1.1 meter aperture Processor Focal Length 16 meter focal length Battery (2) Dynamic Range 11 bit dynamic range with TDI GSD 34 cm Pan, 1.32m MSI Swath 14.5 kmAttitude Actuators Honeywell M-95 CMGs Control CMG Electronics (4) Moment GyrosControl (4)System Sensors Goodrich GR-1004 Star Trackers Star Tracker (2) SIRU Inertial Reference Units Focal Plane PL Electronics Monarch GPS Receiver Radiator (2) Radiator Payload Minimum Agility Acceleration - 1.0 degree/sec2 X-band High Electronics (2) Max Slew Rate – 2.7 degree/sec Gain Antenna Narrowband Two Axis Gimbal Antenna (2)Data Data Recorder 3.2 Terabit High Speed Storage UnitHandling & Sun Sensor (2) GPS Antenna (2)Communications Wideband DL 800 Mbps Dual Pole, X band Tlmy DL 128 Kbps, X band Command UL 64 Kbps, S band See http://www.youtube.com/watch?v=lnv6cDiBF9o 5
  • Satellite Imagery
  • Satellite Orbits
  • 8
  • GeoEye-1 IKONOS GeoEye-29
  • GeoEye Constellation GeoEye Constellation GeoEye Constellation High Resolution Images Move Beyond Mapping› Frequent Access ‒ Mean Time to Access < 1 day› Long Duration Accesses ‒ Average Access Time ~ 1 min/day› High Resolution Access ‒ GeoEye-1: 41 cm Nadir GSD ‒ GeoEye-2: 34 cm Nadir GSD ‒ True 50 cm products› Huge Collection Capacity ‒ IKONOS: 240,000 sqkm/day ‒ GeoEye-1: 350,000 sqkm/day ‒ GeoEye-2: 600,000 sqkm/day Ground Swaths Ground Swaths 10 GE1 = Green IK = Yellow GE2 = Blue GE1 = Green IK = Yellow GE2 = Blue
  • Satellite Image Geometry
  • Ground Sample Distance (GSD) H GSD W GSD› Source image pixels are rectangular, W x H in size› GSD = sqrt(W x H)› A square pixel of GSD x GSD size has the same area as W x H› Product images may be resampled to a different GSD
  • Satellite SatelliteField of View imaging at nadir imaging off nadir› Field of View (FOV) is angle from one edge of an image to the other.› All rays of a high-resolution satellite image are at about the Satellite Field of View same angle. Camera FOV Aerial 90° IKONOS 0.95° GeoEye-1 1.28° GeoEye-2 1.22° Aerial Camera Aerial Field of View camera 13
  • 14
  • Scan Azimuth› Scan Azimuth ‒ Describes scan direction or motion of aim 0° = North point on ground ‒ North-to-South  Scan Azimuth = 180° ‒ South-to-North  Scan Azimuth = 0° 270° = West 90° = East 180° = South West to East Scan azimuth 90° r o N o h uo S h u mz A nac S East to West t t Scan azimuth 270° t i 15
  • Line of Sight (LOS)› The Line of Sight (LOS) is the direction that the camera is imaging.› A Line of Sight direction can be described by azimuth and elevation angles. 16
  • Satellite Collection Geometry 17
  • Azimuth› Azimuth angle ‒ Measured in the horizontal plane 0° = North at the target ‒ Angle from north proceeding clockwise to the projection of the line of sight into the horizontal 270° = West 90° = East plane. ‒ Example: 90° azimuth means the satellite is East of the target 180° = South when the image is taken. 18
  • Collection Azimuth› North Up View 19
  • Collection Azimuth› View from sensor perspective GE1 Image acquired at 53.5° collection azimuth rotated 180° - 53.5° CW on right to view from sensor perspective. 20
  • Elevation› Elevation angle ‒ Measured at target ‒ Angle from horizontal plane up to line of sight.› Alternatives Elevation angle ‒ Incidence or Zenith angle ‒ Off-Nadir or Obliquity angle 21
  • Computing height from shadows & layover DV DV DH DH DV = DH * tan(EL) 22
  • Example: Republic Plaza (Singapore)Image collected at 67° elevation angleLayover measured at 116 mHeight calculationH = 116 m * tan(67°) = 273 mActual height 280 m 23
  • Elevation angle and terrain displacement Zenith Sensor DH = DV / tan(EL) EL Earth DV DEM DH › EL = elevation angle › DV = vertical distance › DH = horizontal distance 24
  • Incidence, Elevation, & Off-Nadir Angles› EL = Elevation = angle at target from horizontal to sensor.› IN = Incidence = angle at target from zenith to sensor.› OB = Obliquity = angle at sensor from nadir to target (off-nadir angle)› IN + EL = 90°  R Cos( EL) › Obliquity is related to elevation by trig formula: OB = ArcSin  e  (H + R )   ‒ Re radius of earth ~ 6371 km =  o e  ‒ Ho = orbit height ~ 681 km 25
  • Incidence, Elevation, & Off-Nadir Angles 26
  • Stereo Geometry Orbit Track About one minute of orbit time between left and right image of a stereo pair. Ground Track Convergence Angle EL2 EL1 About two seconds of orbit time AOI to scan a 15 km by 15 km stereo scene. Longer scans are possible. A 100 km long stereo pair takes about 20 seconds to scan. 27
  • Field of Regard (FOR)› Field of Regard: Angle Range that Camera can Image by rotating› Satellite Field of Regard > 90°.› Field of View can be anywhere within the Field of Regard 28
  • Field of Regard vs. Elevation Angle › Wider Field of Regard at lower elevation angle › Wider Field of Regard from higher orbits 29
  • Field of Regard GSD vs. Cross-Track Distance 1 0.9 0.8 0.7 60° Elevation 60° Elevation Angle GSD, m Angle 0.6 0.5 0.4 IKONOS GE1 GE2 0.3 0 100 200 300 400 500 600 700 800 900 1000 Cross-Track Distance, km RunSatComparison 30
  • Revist Time (time between satellite accesses) 3-day revisit at 40° N at 60° elevation angle › Shorter revisit time at lower elevation angle & higher latitude 31
  • Revisit Time › More frequent revisits at 15 high latitudes because the orbits converge near the 14 7 5 13 poles. 13 6 › Ground stations are located at high latitudes can contact 12 4 the satellite nerly every 11 10 9 orbital revolution. 3 15 1 2 32
  • Pan-MSI Alignment› Each MSI pixel covers 4x4 Pan pixels› 4 multispectral (MSI) bands› 1 panchromatic (PAN) band› Simultaneous PAN/MSI collection› 11-bit resolution 33
  • 4-meter RGB Multispectral 1-meter RGB Pan-Sharpened Color enhancesinterpretation for human visual perception 1-meter Panchromatic 4-meter CIR Multispectral 1-meter CIR Pan-Sharpened 35
  • Camera Models 36
  • Rational Polynomial Coefficient (RPC) Camera Models › RPC Camera Models ‒ Generic mathematical model mapping ground to image coordinates. ‒ Sensor software fits coefficients to physical camera model of image. • Sensors ‒ GeoEye, Ikonos, QB, WV, Cartosat … • Application Software ‒ ERDAS, BAE, PCI, ZI, … › Applications ‒ Block adjust images with ground control to improve accuracy. ‒ Orthorectification ‒ Stereo extraction The mathematics of satellite imagery is The mathematics of satellite imagery is ‒ Photogrammetry complicated, but RPC models are simple complicated, but RPC models are simple
  • Satellite Image Product Geometry
  • Product Geometry Product Rectification Projection Image Model Physical (attitude, Basic Synthetic Array Satellite Scan Path ephemeris & camera calibrations) Geo Constant height Map RPC Ortho DEM Map Ortho Stereo Constant height Path, Map, or Epi-polar RPC or Physical Convergence angle Elevation angle 39
  • BASIC › Photogrammetric Applications › Satellite Projected › Physical Camera Model ‒ High Accuracy › RPC Camera Model ‒ Rapid PositioningIKONOS image of the moon (BASIC product)
  • GEO Tsangpo River Basin, Tibet› Visual Interpretation ‒ Situational awareness ‒ Intelligence ‒ Media› Photogrammetry ‒ Block adjust with other imagery or GCP to improve accuracy. ‒ Orthorectify with DEM to correct for terrain displacement› Map Projected› RPC Camera Model ‒ High Accuracy
  • E BASIC and GEO Products N W E Geo S S East to West ScanN North up Map Projected BASIC GEO RPC Model   Physical Model   Projection Satellite MapBASIC WEast to West ScanSatellite Projected
  • Ortho› Applications ‒ Feature Extraction ‒ GIS Map Base› Terrain Corrected› Map Projected› Mosaics Available Frankfurt Airport, Germany
  • Georectified or Orthorectified?› Georectified Constant Height Line of Sight Topographic ‒ Terrain displace- Surface ment errors ‒ Quick, Low cost› Orthorectified Topo- graphic ‒ DEM corrects for Surface terrain Ortho- displacement rectified Image ‒ Accuracy for mapping 44
  • Geospatial eXploitation Products™What is an Orthophoto?• An orthophoto is an image that Camera has had all distortion due to Original Image camera obliquity, terrain relief, and features removed.• The SOCET GXP Ortho Manager converts one or more original images into an orthophoto by transforming the pixels to their Orthophoto proper position according to the given sensor, terrain, and feature information.• In the final product all points in the image appear as if the DTM observer were looking down from nadir position. March, 2009
  • Orthorectified
  • Georectified
  • Stereo› Attributes ‒ High resolution ‒ Color ‒ 3-dimensional› Applications ‒ DEM extraction ‒ 3D feature extraction ‒ Geomorphic visualization Stereo RPC Physical Projection Model Model Satellite   Map   Epi-Polar   48
  • Stereo Image Of Downtown Denver, Colorado
  • Thank You! Big Bear Glacier, Alaska