Enhanced Absolute and Relative Radiometric Calibration for Digital Aerial Cameras

A new laboratory radiometric calibration process has been developed at Intergraph Z/I Imaging and is being implemented for both the DMC and RMK-D camera systems. This new capability enables the development of absolutely radiometrically calibrated products for scientific and remote sensing applications and improves general image color quality and color balance. Although many advanced CCD-based multispectral cameras are capable of being absolutely radiometrically calibrated, their benefits have not been widely exploited by the multispectral aerial remote sensing community. Many quantitative scientific studies incorporating vegetation indices, time series analyses, and change detection require absolute radiometry and atmospheric correction to generate surface reflectance. Dark scenes such as those produced by water and dense vegetation also require atmospheric correction, as atmospheric scatter can easily mask features. Consequently absolute radiometric calibration of aerial digital imagery enhances its utility and improves its ability to be fused with other data sets such as digital elevation data to generate new products. The new laboratory capability enables Z/I Imaging to generate radiometric performance characteristics comparable to those obtained from remote sensing satellite systems. It gives remote sensing scientists a new tool to augment their satellite imagery and is particularly useful in regions of the world that are difficult to acquire with satellite systems because they experience significant cloud cover. This paper discusses absolute and relative radiometry and gives an overview of the new calibration procedure established at Z/I Imaging. 1. RADIOMETRY AND REMOTE SENSING A new digital camera radiometric calibration laboratory process, traceable to national standards, has been developed at Intergraph Corporation’s Z/I Imaging. This new procedure will be implemented for the Z/I Imaging Digital Mapping Camera (DMC) (Heier et al., 2001; Madani, 2004; Neumann, 2003) and the new RMK-D camera system (Intergraph, 2009). The RMK-D is a medium-format camera system with high geometric resolution, 14 bits per pixel radiometric resolution, 70 dB dynamic range, digital forward motion compensation and four-band multi-spectral capability. These calibration procedures, which have been applied to both panchromatic and multispectral camera heads, will not only improve general image color quality and color balance, but will also enable the development of absolutely radiometrically calibrated products for scientific and remote sensing applications. The newly developed process will enable Z/I Imaging digital aerial cameras to produce radiometrically calibrated imagery with an absolute accuracy comparable to that achievable from both commercial and government satellite remote sensing systems. This level of absolute radiometry will make it possible for Z/I Imaging digital camera users to perform traditional remote sensing tasks that historically were limited to those teams using satellite imagery. It will also allow users of satellite imagery to augment and enhance their projects with aerial digital camera data products. Multispectral aerial digital imaging systems have traditionally focused on relative radiometric calibrations to cosmetically correct image defects. Typically, image normalization or flat fielding and camera head-to-camera head corrections are used to remove the effects of vignetting and most pixel-to-pixel variations in response. A typical remote sensing industry relative radiometry goal after flat fielding calibration is to have less than 1% variation between pixels (Landsat Data Photogrammetric Week '09 Dieter Fritsch (Ed.) Wichmann Verlag, Heidelberg, 2009