September 17-20, 2007, Nessebar, Bulgaria VIIth International Scientific and Technical Conference From Imagery to Map: Digital Photogrammetric Technologies Master class: Photogrammetric processing of pushbroom satellite images Petr S. Titarov, Software Developer September 17-20, 2007, Nessebar, Bulgaria

Master class layout I. Basics of space pushbroom imaging Pushbroom imagery acquisition Pushbroom imaging modes Pushbroom stereopairs acquisition methods Pushbroom images blocks Parameters of pushbroom imaging systems II. Pushbroom photogrammetry Photogrammetric processing problems Methods of pushbroom photogrammetry III. Pushbroom imaging systems overview Systems of resolution 1 meter and better Systems of resolution about 2 meters Systems of resolution 5 meters Systems of resolution 10-20 meters IV. Taking choice of remote sensing product for photogrammetry V. Satellite pushbroom imagery processing using PHOTOMOD

Part I Basics of space pushbroom imaging Pushbroom imagery acquisition Pushbroom imaging modes Pushbroom stereopairs acquisition methods Pushbroom images blocks Parameters of pushbroom imaging systems

Pushbroom image acquisition Line-by-line (pushbroom) Pixel by pixel (whiskbroom) Geometry of pushbroom imagery significantly differs from central projection one, so the classical photogrammetric methods are not applicable.

Pushbroom imaging modes Synchronous pushbroom imaging mode Sensor attitude is kept constant during the image acquisition long strips acquisition is possible the mode simplifies image geometry Most of current imaging systems work in a synchronous way: IKONOS SPOT 1-5 IRS 1C/1D/P5/P6 FORMOSAT-2 Terra ALOS …and others.

Pushbroom imaging modes Asynchronous pushbroom imaging mode Sensor attitude is rapidly changing during the image acquisition: to enlarge the exposure to make vector-scenes (not parallel to the satellite track) Asynchronous mode is incident to high-resolution imaging systems like: EROS A QuickBird

Pushbroom stereopairs acquisition methods Cross-track stereo imaging Cross-track (roll) tilting possibility is required Two similar satellites can be used Systems implementing this way of stereo imaging are, for example SPOT 1-5 (сенсоры HRV, HRVIR, HRG) IRS 1C/1D

Pushbroom stereopairs acquisition methods Along-track stereo imaging retargeting the sensor Short time gap between the stereopair images acquisition High satellite agility is required Systems implementing this way of stereo imaging are, for example: IKONOS EROS

Pushbroom stereopairs acquisition methods Along-track imaging using two sensors mounted on the same satellite SPOT 5/HRS Cartosat-1 ALOS Terra/ASTER Short time gap between the stereopair images acquisition Constant base-to-height ratio Long stereo strips can be acquired

Blocks of pushbroom images Block of single images (“monoblock”) New (ordered) imaging Base-to-height ratio (B:H) in the overlapping areas is arbitrary. Block composed of archive images

Blocks of pushbroom images Block of stereopairs (“stereoblock”) The set of overlapping stereopairs

Pushbroom imaging systems parameters Geometric parameters: Ground sample distance Depends on: detector size focal length orbit altitude Tilting capability Depends on: sensor and satellite design Swath width Depends on: focal length < the two determine detectors size and count < the field of view orbit altitude tilting Example: SPOT/HRG

Pushbroom imaging systems parameters The main radiometric parameters Spectral channels Count and the wavelength range Radiometric resolution Dynamic range Imaging system productivity Depends on: swath width satellite orbit tilting capability imaging mode (synchronous/asynchronous) stereoscopic imaging method on-board storage capacity parameters and placement of receiving stations

Remote sensing satellites orbits Major semi-axis a determines the satellite altitude Eccentricity e0 (circular orbit) constant satellite altitude Inclination i98 (near-polar sun-synchronous orbit) almost all the Earth is observable satellite passes nodes every revolution at the same local time Celestial longitude of the ascending node  subject to perturbation Argument of perigee  does not matter for circular orbit Secular perturbation per N revolutions: Geo-synchronous orbit satellite track periodically repeats

Remote sensing satellites orbits Sun-synchronous orbit Polar orbit Sun-synchronous orbit

Pushbroom photogrammetry Part II Pushbroom photogrammetry Problems solved to perform photogrammetric processing Methods of pushbroom photogrammetry

Space resection and space intersection Single images Orthoimagery 2D vectors Ortho- mosaics Export to GIS, CAD, digital maps GCPs DEM Stereopairs DEM 3D vectors GCPs

Methods of pushbroom photogrammetry Rigorous Generic Replacement models Modeling imagery acquisition geometry Using a-priory relationships containing parameters determined from GCPs Using abstract relationships that approximate rigorous imaging model

Rigorous method l – line number Reconstruction of: Ray’s edges: Ray’s directional vectors: l – line number p – detector number Models used: Sensor motion model: Sensor geometry model: Attitude model: Reconstructed vectors: Ray’s edge: Ray’s directional vector:

Sensor geometry (interior orientation) The model defines the directional vector of ray sensed by the detector number p with respect to the sensor reference system S: The model is the analog of interior orientation elements in classical photogrammetry. 2D central projection Tabulated vector-function p p1 p2 

Parameters to be refined: Sensor motion model Polynomial model Orbital model Keplerian orbit parameters: major semi-axis a eccentricity e inclination i celestial longitude of the ascending node  argument of perigee  perigee passing time  Parameters to be refined: e, i, ,, sometimes a Parameters to be refined: Ai , Bj , Ck applicable in any Cartesian reference system (including ECR) simple to implement inertial reference system must be used physical model only a few parameters to refine

Sensor attitude model The model defines the rotation of the sensor reference system with respect to the geocentric Reference system. The model is defined by the three angles , , , which polynomially depend on the line number l, or it can be represented as the sum of the measured in-flight values and polynomial refinements:

Rigorous solution of space resection and space intersection Iterative process Correspondent rays intersection

The image orientation is based on the collinearity condition: Imagery orientation The image orientation is based on the collinearity condition: Any two of the three equations are independent:

Generic (parametric) method Using some a-priory equations derived from coarse assumptions concerning imaging geometry which relate image coordinates x, y to ground ones X,Y,Z. The values of the parameters involved into the equations are calculated using GCPs. Parallel-perspective model Direct Linear Transformation (DLT)

Replacement models They are models which approximate ground-to-image correspondence calculated using rigorous method: or, more often,

RPC = Rational Polynomial Coefficients = Rapid Positioning Capability Basic relationships: , where N, N, hN - normalized ground coordinates: (-1 N 1, -1 N 1, -1 hN 1) xN, yN - normalized image coordinates: (-1 xN 1, -1 yN 1) Adjustment-derived refinements: или

Algebraic solution of space intersection and space resection Based on relationships: Space intersection Space resection Least-squares estimation of 3 unknowns X, Y, Z from 4 non-linear equations: Directly by formula

Pushbroom imaging systems overview Part III Pushbroom imaging systems overview Systems of resolution of 1 m or better Systems of resolution about 2 m Systems of resolution 5 m Systems of resolution 10-20 m

Systems of resolution 1 m or better

Systems of resolution 1 m or better

Systems of resolution about 2 m

Systems of resolution 5 m

Systems of resolution 10-20 m

Taking choice of remote sensing product for photogrammetry Part IV Taking choice of remote sensing product for photogrammetry One should take into consideration the following aspects: if the imagery is geometrically pre-processed metadata contents (if it contains the image geometry) possibility to order polygones or sub-scenes data format

Geometric preprocessing Rigorous methods are not applicable to the geometrically preprocessed imagery! Example: Imaging system Remote sensing product Geometrically raw Geometrically corrected SPOT, ASTER 1A 1B KOMPSAT, Landsat 1R 1G QuickBird Basic Standard OrbView-3 BASIC GEO

Metadata contents and data file format Cartosat-1 stereopair Stereo Ortho Kit Basic stereo TIFF raster and RPC Super Structured file format, processing using generic methods

Satellite pushbroom imagery processing using PHOTOMOD Part V Satellite pushbroom imagery processing using PHOTOMOD

PHOTOMOD supported sensors

Remote sensing product files set structure QuickBird Basic product files set Connection between IKONOS Geo Ortho Kit product imagery and RPC files <image file name>.tif <image file name>_rpc.txt

QuickBird Standard Tiled Structure QuickBird Standard and Standard Ortho Ready imagery can be tiled. RPC refers to the composed image!

Collective processing of imagery acquired by different sensors Possible candidates for collective processing: SPOT-5 Supermode (2.5 m) + FORMOSAT 2 PAN (2 m) IKONOS + OrbView-3 + Kompsat-2

Thank you for your attention!