Sensor Modelling and Validation for Linear Array Aerial and Satellite Imagery
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Beschreibung
The Linear Array CCD technology is widely used in the new generation aerial photogrammetric sensors and also in the high-resolution satellite optical sensors. In comparison to the Matrix (frame/area) Array sensors, the Linear Array CCD sensors have smaller number of detectors to cover the same swath width. In addition, the flexibility is higher in the physical sensor design. The conventional film cameras used in aerial photogrammetry are manufactured in frame format. The first remote sensing sensors for Earth observation employed film cameras as well. The recent sensor technologies of the optical remote sensing satellites are replaced with the Linear Array CCDs. In case of the aerial photogrammetric sensors, medium and small format aerial cameras are produced only in the frame format. The development in large format cameras is twofold. The Linear Array CCD and Matrix Array CCD sensors have been present in the industry since the year 2000.
Due to the geometric differences between the Linear Array cameras and the frame cameras, the conventional photogrammetric procedures for the geometric processing of the Linear Array CCD images should be redefined or newly developed. The trajectory modeling is one of the main concepts, which entered into the field of photogrammetry with the aerial and satellite pushbroom sensors. The modified collinearity equations are extended with mathematical functions to model the image trajectory in the bundle adjustment. This study encompasses the triangulation of Linear Array CCD images with the use of different trajectory models. The self-calibration models are partially adapted from the frame sensors in accordance with the physical structures of the Linear Array CCD sensors.
In general, the triangulation and self-calibration of the aerial and the satellite Linear Array CCD images show similarities in terms of trajectory modeling and the physical definitions of the additional parameters. The main difference is in the number unknown parameters defined in the bundle adjustment, which is calculated as a function of the number of lenses, the trajectory model configuration, and the number of Linear Array CCDs used in the sensor. Therefore, similar sensor modeling and calibration approaches are applied in this study, with necessary adjustments for each system.
In order to obtain high accuracy point positioning, high quality image trajectory measurement is crucial. The given trajectory can be modeled in the adjustment by using constant and linear correction parameters, as well as higher order polynomials. This study investigates the three different trajectory models with three different mathematical approaches. Two of the models are investigated at different levels of sophistication by altering the model parameters.
Two different aerial Linear Array CCD sensors, the STARIMAGER of former Starlabo Corporation, Japan, and the ADS40 sensor of the Leica Geosystems, Heerbrugg, are used for the practical investigations. The PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping) onboard of Japanese ALOS satellite launched by JAXA (Japan Aerospace Exploration Agency) in 2006 is the satellite Linear Array CCD sensor used for the application parts of this study. The two aerial Linear Array CCD sensors work with the TLS (Three-Line-Scanner) principle. Three or more Linear Array CCDs are located in the focal plane of a single lens with different viewing angles providing stereo capability. The PRISM sensor differs in the optical design with three camera heads, each associated with a different viewing angle.
Due to the design differences between the sensors, two sets of additional parameters for self-calibration are applied in this study. The aerial TLS sensors share the same set of additional parameters due to similar interior geometries of the sensors. The self-calibration of the PRISM sensor uses a different set due to multiple lenses and also multiple CCD chips used to form each image line.
The sensor orientation and calibration methods presented in this study are validated using a number of application datasets. The image datasets of the three sensors are acquired over specially established testfields. Triangulation results prove the importance of high quality trajectory measurements for accurate sensor orientation. When the given image trajectory has a low quality, a sophisticated trajectory model should be used together with a high number of ground control points.
This study also shows that, despite their weaker sensor geometry, the Linear Array CCD sensors have reached the accuracy potential of the conventional frame imagery for point determination. In addition, similar to the conventional film sensors, self-calibration has proven as a powerful tool for modeling the systematic errors of the Linear Array CCD imagery, albeit the method should be applied with a great care.
Autor*in
Sultan Aksakal-Kocaman
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