DETERMINATION of THE INDIRECT ORIENTATION of ORBITAL PUSHBROOM IMAGES USING CONTROL STRAIGHT LINES

The aim of this paper is to present an experimental assessment of two models that use "control lines'' for the indirect orientation of pushbroom imagery. Since pushbroom image acquisition is not instantaneous, six exterior orientation parameters (EOPs) must be estimated for each scanned line. The sensor position and attitude parameters are modelled with a time-dependent polynomial. The relationship between a straight line in the image space and its homologous form in the object space is established in the first model, based on the principle that the position vector containing an image point (projection ray) and the vector normal to the projection plane in the object space are orthogonal. The second model is based on the equivalence between the vector normal to the projection plane in the image space and the vector normal to the rotated projection plane in the object space. The equivalence property between planes was adapted to consider the pushbroom geometry. A model based on collinearity equations using points adapted to the pushbroom geometry was also implemented, aiming at a comparison of the methodologies. Six experiments using different sets of observations for indirect estimation of EOPs of images from the China-Brazil Earth Resources Satellite (CBERS) were carried out, by varying the geometric distribution and the number of straight lines. Also, experiments combining points and straight lines were accomplished. The results showed that an accuracy of around twice the ground sample distance (GSD) in the check points can be achieved with the models studied, which can then be used to estimate the EOPs of pushbroom images. Several other factors affecting the accuracy, such as the distribution and number of control features, were also assessed.