Geometric Calibration of an Aerial Multihead Camera System for Direct Georeferencing Applications

An aerial multihead camera consists of a photogrammetric system composed of multiple cameras, which are mounted together in a main structure. By combining the images acquired simultaneously from each camera, a single synthetic image with much larger coverage can be generated. Such systems are usually integrated with a position and orientation system (POS) to perform direct georeferencing (DG) or integrated sensor orientation (ISO). However, to obtain mapping products with high accuracy through a DG procedure, it is essential the implementation of the system geometric calibration. Usually, the aerial multihead camera manufacturers perform the geometric calibration using laboratory methods and only the camera interior orientation parameters (IOPs) and their relative orientation parameters (ROPs) are determined to generate the synthetic image (process known as "platform calibration"). The mounting parameters (lever arms and boresight misalignment angles) relating the synthetic image and GNSS/INS reference systems are usually defined using nominal installation values. The objective of this paper is to present an in-flight calibration methodology for multihead camera systems and its assessment for DG applications. The introduced methodology involves three steps: 1) determination of the cameras' IOPs and their ROPs; 2) synthetic image generation; and 3) refinement of the IOPs of the synthetic image and the mounting parameters determination between the synthetic image and GNSS/INS reference systems using different methods. The results of the experiments shown the viability of the proposed methodology for DG applications involving photogrammetric procedures for large-scale mapping requirements.