Optimum estimator for SPOT-pan and ALS-lidar intensity image registration via tie points

Abstract

The characteristics of a Système Pour d’Observation de la Terre (SPOT) panchromatic image of a geographic area such as an airfield are different from those of an airborne laser scanner lidar intensity image of the same area. This study investigates the feasibility of locating tie points shared by the target (airborne lidar-intensity) and search (spaceborne SPOT-pan) images. At an approximate point position, image segmentation and enhancement are employed so that a pair of target and search window images tend to resemble each other. The similarity is then measured by utilizing a least-squares image matching algorithm which involves variance-component estimation. The proposed method has a 3–15% higher success rate than an equal-weight matching method. Coordinate differences of the conjugate image points serve as reference value to be used in the least-squares collocation method for pixel-by-pixel transformation. The image registration accuracy from a SPOT-pan to a lidar intensity image is estimated to be ±1.0 pixel.

Keywords:

• Harris corner detector
• image matching
• variance-component estimator
• image registration

Acknowledgments

The authors feel indebted to the National Science Council for research grants. They would also like to thank the environmental specialists at the Industrial Technology Research Institute for making available the ALS image dataset. The comments by anonymous reviewers were very constructive, making for a much clearer text after revision.