Integration of sensors for photogrammetry and remote sensing 8 th semester, MS 2005

Image geometry, georeferencing, orthorectification Specifications of VHR sensors for RS Camera models for IKONOS Specifications for IKONOS products Task: georeferencing of a Radar image

Overview on operational satellite sensors Resolution Swath (nadir) QB PAN 0.61m MS 2.44 m 16.5 km IKONOS PAN 1m MS 4 m 13.5 km SPOT 5 PAN + MS 2.5 m, 5m MS 10 m 60 km 120 km LANDSAT 7 PAN 15 m MS 30 m 185 km

VHR sensors for RS Specifications Orbital geometry Sensor geometry Image acquisition (‘agility’) Exterior orientation Interior orientation Spectral resolution Radiometric resolution Spatial resolution Temporal resolution

Orbit geometry Determines: how much of Earth surface can be covered how often the satellite revisit the same location Sun-synchronous orbits Altitude Orbit inclination

Sensor geometry Frame photogrammetric cameras, central projection Point across-track scanner Line along-track scanner Panoramic

Across-track scanner (whiskbroom) A.Oscillating mirror B.Detectors C.Instantaneous field of view (IFOV) D.Ground sampled distance (GSD) E.Angular field of view F.Swath Geometry not as stable as for line sensors Distortions due to a scanner mirror rotation Variations of the resolution cell size One-dimensional relief displacement Flight parameter distortions (roll, pitch, ‘crab’) Application: thermal scanners

Along-track scanner (pushbroom) A.Linear array of detectors B.Focal plane of the image C.Lens D.GSD Geometric integrity of a linear array of detectors Parameters of EO for each line Perspective along the scan line, orthographic in the direction of flight Calibration for each detector Limitation in spectral sensitivity

Image acquisition geometry Viewing directionNadir angle Stereo views cross-track along-track nadir forward backward nadir position off-nadir

IKONOS - image acquisition geometry

IKONOS – stereo image collection

Exterior orientation = satellite ephemeris and attitude Example: IKONOS Determination of ephemeris -post-processing of on-board GPS data Determination of attitude -measuring of star trackers + gyroscopes Important: relation between the satellite attitude co-ordinate system and the sensor co-ordinate system (pre-launched measurements + in-flight calibration)

Interior orientation Layout of the detector array, usually placed in the focal plane Optical distortion parameters Example : IKONOS Field Angle Map -allows to determine the line of sight vector for each pixel in the sensor co-ordinate system

Spectral resolution

Spatial resolution Nadir angle0°0°10°20°30°40°50° Pan across view direction Pan along view direction MS across view direction MS along view direction IKONOS: ground sampled distance [m] depending upon view direction

Radiometric resolution = number of bits used for a multispectral band  IKONOS: 11-bit Temporal resolution IKONOS:  = 40 , GSD = 1 m, revisit time 2.9 days

IKONOS camera model defines relation between object and image co- ordinates based on interior and exterior orientation parameters of the sensor specified by a provider of the sensor/system (Spaceimaging) complex, difficult to implement for a user simplification by ‘replacement camera models’ Rational Polynomial Camera (RPC) model Direct linear transform (DLT) model Affine model

Physical camera model Position of projective centre (PC) and attitude angles change from scan line to scan line

Rational Polynomial Camera (RPC) model relation between object co-ordinates (φ,λ,h) and image co-ordinates (r,c) given by rational polynomial functions: r’ = f r (φ’,λ’,h’)/g r (φ’,λ’,h’) c’ = f c (φ’,λ’,h’)/g c (φ’,λ’,h’) x’ … normalised co-ordinates x’ = (x-x_offset)/x_scale

Rational polynomial functions usually, 3 rd order polynomials are used f r = a 1 +a 2 φ’+a 3 λ’+a 4 h’ +a 5 φ’λ’+a 6 λ’h’+a 7 φ’h’+a 8 λ’ 2 +a 9 φ’ 2 + +a 10 h’ 2 +a 11 φ’λ’ h’+a 12 λ’ 3 +a 13 φ’ 2 λ’+a 14 λ’h’ 2 +a 15 φ’λ’ 2 + +a 16 φ’ 3 +a 17 φ’ h’ 2 +a 18 λ’ 2 h’+a 19 φ’ 2 λ’+a 20 h’ 3 g r = b 1 +b 2 φ’+b 3 λ’+b 4 h’ +b 5 φ’λ’+b 6 λ’h’+b 7 φ’h’+b 8 λ’ 2 +b 9 φ’ 2 + +b 10 h’ 2 +b 11 φ’λ’ h’+b 12 λ’ 3 +b 13 φ’ 2 λ’+b 14 λ’h’ 2 +b 15 φ’λ’ 2 + +b 16 φ’ 3 +b 17 φ’ h’ 2 +b 18 λ’ 2 h’+b 19 φ’ 2 λ’+b 20 h’ 3 similarly, RPC coefficients c 1, …, c 20, d 1, …, d 20 in functions f c and g c

RPC coefficients calculated in least-squares adjustment from 3D grid points co-ordinates of 3D grid points generated using a physical camera model comparison of RPC and a physical camera model max. error using independent check points 0.04 pel RMS error using independent check points 0.01 pel (Grodecky, J., Dial, G., IKONOS geometric accuracy, Space Imaging, 2001)

3D grid for derivation RPC coefficients

Refinement of RPC model improving absolute positional accuracy of the georeferenced image by adding GCPs finding parameters of affine transformation r corr =a 1 +a 2 r’+a 3 c’ c corr =b 1 +b 2 r’+b 3 c’ improvement of accuracy from several m up to 0.5m if accurate and well distributed GCPs are available

Other replacement camera models Direct linear transform model derived from collinearity equation (projective geometry) x=(a 1 +a 2 X+a 3 Y+a 4 Z)/(c 1 +c 2 X+c 3 Y+c 4 Z) y=(b 1 +b 2 X+b 3 Y+b 4 Z)/(c 1 +c 2 X+c 3 Y+c 4 Z) Affine model x=a 1 +a 2 X+a 3 Y y=b 1 +b 2 X+b 3 Y

Product Horizontal accuracy [m] Ortho- rectification GCPDEM Geo15--- Reference25+-±22m Pro10+-±10m Precision4++±10m Precision Plus2++±3m IKONOS products IKONOS product guide

Links Articles: –Grodecki, J., Dial, G. (2001).: IKONOS Geometric Accuracy. Proceedings of Joint Workshop of ISPRS Working Groups I/2, I/5 and IV/7 on High Resolution Mapping from Space 2001, University of Hanover, Hanover, Germany, Sept , 2001IKONOS Geometric Accuracy. Products description –Space Imaging (IKONOS)Space Imaging –DigitalGlobe (QuickBird)DigitalGlobe