Abstract: A method of assembling a transformer core in which a lamination of rectangular plates formed of a magnetic material is inserted in the spaces in primary and secondary transformer coils, and in which the opposite ends of the lamination are brought into abutment each other to form the lamination into an annular shape. The lamination of the magnetic material plates is bent into a U-like shape with the transformer coils thereon and is magnetized by energizing the transformer coils, while the opposite ends of each magnetic material plate are restrained from being brought closer to each other. The opposite ends of the laminated magnetic material plates are successively released from the restrained state from the innermost opposed ends of the U-like shape to attract and closely contact each other by the magnetic force.

Abstract: A system for detecting underground objects is disclosed wherein image data obtained through a deep range-migration correction and image data obtained through a shallow range-migration correction are combined so that data at the corresponding positions on both the image data at high level may mutually intensify, whereas other data may mutually weaken. The target spot on the thus combined image data is made sharp and provides sufficently high resolution.