Small-format Digital Camera: a Study into Stability Analysis

In the last years, small and medium format digital cameras have become a potential tool for photogrammetric applications due to its convenience, availability and quick image acquisition and processing. In addition, the resolution of these cameras has significantly increased while their price decreased. However, to extract accurate and reliable 3D metric information from images, an important condition should be considered: Are the interior and exterior orientation parameters accurate enough for photogrammetric applications? Generally, the camera calibration procedure is performed using a target or a linear test field, regardless of the photogrammetric project that will be later performed. For photogrammetric applications, the camera should be stable and the interior orientation parameters not vary with time. In addition, the exterior orientation parameters of the images should be accurately determined. The exterior orientation parameters can be determined by indirect or direct geo-referencing. Traditionally, using ground control points and bundle adjustment, the indirect method is often performed. The direct method is applied when GPS/INS data are available onboard the imaging platform. Considering airborne photogrammetric mapping, the digital camera generally is carried on planes and exposed to different temperatures from the one registered during the calibration procedure. Two aspects should be discussed: Did the interior parameters change? Will the changes modify the quality of the derived information? In the paper we try to answer these questions. The digital camera Sony DSC-F828 is calibrated under different temperatures to determine the geometric stability through a great temperature variation. The camera is calibrated at different times, varying the environmental temperatures from close to zero to twenty-five degrees Celsius. A special procedure is used to achieve temperatures close to zero degrees that enable to take good quality pictures. Two external target testfields are used to perform all experiments. The camera was calibrated no less than twice at each temperature. The geometric stability analysis at different temperatures and epochs is presented and discussed. In addition, airborne photogrammetric experiments, using different sets of interior orientation parameters, are performed to stability analysis at different environmental temperatures. Finally some conclusions are drawn from the experimental results, and future recommendations are proposed. * Corresponding author.