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Abstract : |
Abstract: Several space-borne cameras use pushbroom scanning to acquire imagery. Traditionally,modeling and analyzing these sensors has been computationally intensive due to the motion of the orbiting satellite with respect to the rotating earth, and the non-linearity of the mathematical model involving orbital dynamics. A new technique for mapping a 3-D point to its corresponding image point thatleadstofastconvergence is described. Besides computational e ciency, experimental results also con rm the accuracy of the model in mapping 3-D points to their corresponding 2-D points. 1 Pushbroom Sensors The pushbroom principle is commonly used in satellite cameras for acquiring 2-D images of the Earth surface. SPOT satellite's HRVcameraisawell-known example of a pushbroom system [1]. In general terms, a pushbroom camera consists of an optical system projecting an image onto a linear array of sensors. At any time only those points are imaged that lie in the plane de ned by the optical center and the line containing the sensor array. This plane will be called the instantaneous view plane or simply view plane (see [2] for details). This optical system is mounted on the satellite and as the satellite moves, the view plane sweeps out a region of space. The sensor array, and hence the view plane, is approximately perpendicular to the direction of motion. The magnitude of the charge accumulated by each detector cell during some xed interval, called the dwell time, gives the value of the pixel at that location. Thus, at regular intervals of time 1-D images of the view plane are captured. The ensemble of these 1-D images constitutes a 2-D image. It should be noted that one of the image dimensions depends solely on the sensor motion. It is well known that the standard photogrammetric bundle adjustment typical of aerial imagery does not work for satellite imagery [3, 2]. Even if one were to model the ortho-perspective nature of the imagery, classical space resectioning is unable to separate the correlation among the unknown parameters. For accuracy, and in fact convergence, a pushbroom camera model must explicitly take into account the constraints imposed by: (1) the Kepler's Laws, (2) the rotation of the earth, and (3) the constraints imposed by the ephemeris data., |
