Digital metric camera radiometric and colorimetric calibration with simultaneous CASI imagery to a CIE standard observer based colour space

Abstract

The Institut Cartogràfic de Catalunya (ICC) operates a Digital Metric Camera (DMC), manufactured by Z/Imaging. It supports the simultaneous capture of panchromatic, RGB colour and near-infrared images. One of the most important ICC products is the Catalonia orthophotomap series. This product is intended to depict the territory as realistically as possible. With this aim, ICC is developing a project to obtain genuine colours in the photographic products produced with the DMC camera and this paper contains some preliminary results. Since an absolute radiometric calibration of the DMC is not available yet, this is accomplished through simultaneous images acquired with both DMC and a Compact Airborne Spectral Imager (CASI) also operated by ICC. These images are used to locate common areas imaged in similar geometrical conditions, and then a linear relationship between Digital Numbers (DN) from DMC and radiance values of a CASI image emulating DMC bands is calculated. To improve the colour of the DMC products, a colorimetric calibration based on polynomial transformations has been developed. This transformation allows changing from DMC-RGB space to a sRGB space that is based on CIE-XYZ colour space. Airborne ICC-CASI images acquired with a Cessna Caravan B20 over Banyoles (Spain) in 2005 were used to test the methodology. The comparison between the training colours and the ones obtained after colorimetric calibration yield differences in 8bit DN that range from 4 to 36 DN with a mean value of 12 DN. The effect was also visually analyzed on different subsets of images that include agriculture areas, urban landscape and a natural water layer. Finally, it was found that the application of both calibrations to the DMC images results in a consistent colour combinations for all the analyzed subsets.

Digital Airborne Photogrammetry—A New Tool for Quantitative Remote Sensing?—A State-of-the-Art Review On Radiometric Aspects of Digital Photogrammetric Images

“…Relative radiometric calibration normalizes the output of the sensor so that an uniform response is obtained in the entire image area when the focal plane of the sensor is irradiated with a uniform radiance field; for a single band, the corrections are determined at least for sensitivity differences of individual cells of a CCD array, defect pixels, light falloff, and dark signal [36,37]. Spectral response calibration determines the system's response as a function of wavelength for each channel [33,35] and colorimetric calibration determines the relationship between the sensor and standard color spaces [38]. PSF-calibration determines the system's response to a point source [1].…”

“…In Finland, comprehensive campaigns with various systems have been carried out at the Sjökulla test field [1,2,13,50]. Institut Cartogràphic Catalonia (ICC) has performed comprehensive campaigns with DMC at the Banyoles test field [38,51,52]. The German Society for Photogrammetry and Remote Sensing (DGPF) carried out test flights with many systems at the Vaihingen/Enz test field in Germany in the summer of 2008 [53].…”

“…Intergraph Image Station PixelQue [64], BAE Systems Socet Set Dodger [65] and Ortho Vista [66]). Several organizations are currently developing radiometric block adjustment software [11,38,51,67]; methods from remote sensing systems are being modified and they are entering the photogrammetric processes.…”

“…ICC and IGN utilize their own radiometric block adjustment methods (Section 2.5.1) [38,51,67]. Other software used are the methods included in photogrammetric software (e.g.…”

Radiometric stability assessment of an airborne photogrammetric sensor in a test field

“…The empirical investigations of radiometric properties of the large-format digital photogrammetric sensors have shown that they have high radiometric performance potential, including linearity, large dynamic range, great radiometric resolution and they are suited for radiometric calibration (Honkavaara and Markelin, 2007;Markelin et al, 2008;Martínez et al, 2007; Arbiol, 2008). However, many questions still concern the entire processing chain of photogrammetric images (Honkavaara et al, 2009).…”