Wolfgang Kornus

Geometric in-flight calibration of the stereoscopic line-CCD scanner MOMS-2P

This paper describes the geometric in-flight calibration of the Modular Optoelectronic Multispectral Scanner MOMS-2P, which has collected digital multispectral and threefold along-track stereoscopic imagery of the earths surface from the PRIRODA module of the Russian space station MIR from October 1996 to August 1999. The goal is the verification and, if necessary, the update of the calibration data, which were estimated from the geometric laboratory calibration. The paper is subdivided into two parts, describing two different procedures of geometric in-flight calibration. The first method is based on DLR matching software and is restricted to nadir looking channels, which are read out simultaneously. From a high number of individual point matches between the images of the same area taken by the different CCD arrays, the most reliable ones are selected and used to calculate shifts with components in and across flight direction between the CCD arrays. These actual shifts are compared to the nominal shifts, derived from the results of the laboratory calibration, and parameters of the valid camera model are estimated from both data sets by least squares adjustment. A special case of band-to-band registration are the two optically combined CCD-arrays of the nadir high-resolution channel. They are read out simultaneously with a nominal 10 pixel overlap in stereoscopic imaging mode A. The DLR matching software is applied to calculate the displacement vector between the two CCD-arrays. The second method is based on combined photogrammetric bundle adjustment using an adapted functional model for the reconstruction of the interior orientation. It requires precise and reliable ground control information as well as navigation data of the navigation-package MOMS-NAV. Nine contiguous image scenes of MOMS-2P data-take T083C building an about 550-km-long strip over southern Germany and Austria taken in March 1997 were evaluated. From both procedures calibration data are estimated, which are presented and compared to the lab-calibration results.

Orientation of MOMS-02/D2 and MOMS-2P/PRIRODA imagery

Abstract This paper deals with the orientation of three-line imagery which has been taken during the MOMS-02/D2 experiment in spring 1993, and during the MOMS-2P/PRIRODA mission since April 1996. The reconstruction of the image orientation is based on a combined adjustment of the complete image, ground control, orbit and attitude information. The combined adjustment makes use of the orientation point approach or the orbital constraints approach. In the second case, the bundle adjustment algorithm is supplemented by a rigorous dynamical modeling of the spacecraft motion. The results of the combined adjustment using MOMS-02/D2 imagery and control information of orbit #75b are presented. Based on the orientation point approach an empirical height accuracy of up to 4 m (0.3 pixel) is obtained. In planimetry the empirical accuracy is limited to about 10 m (0.7 pixel), since the ground control points (GCP) and check points could not be identified in the imagery with the required accuracy. Computer simulations on MOMS-2P/PRIRODA image orientation based on realistic input information have shown that good accuracies of the estimated exterior orientation parameters and object point coordinates can be obtained either with a single strip and a few precise GCP or even without ground control information, if a block of several overlapping and crossing strips with high geometric strength (q≈60%) is adjusted.

Photogrammetric point determination using MOMS-02/D2 imagery

During the second German spacelab mission D2, successfully flown in spring 1993, the Modular Opto-electronic Multispectral Scanner MOMS-02 acquired digital high resolution, along track, 3-fold stereoscopic imagery of the earth surface. The scientific processing of the data is conducted by several German university institutes and the German Aerospace Research Establishment (DLR). The major goal is to realize the entire photogrammetric processing chain using digital MOMS-02 imagery. The emphasis of this paper is put on the photogrammetric point determination using MOMS-02 panchromatic 3-line imagery of Australia (D2-orbit 75b). Two independent sets of conjugate image points were derived at Stuttgart University using a feature based matching approach and also at the Technical University Munich using a modified Otto/Chau region growing algorithm which had previously been applied to SPOT and airborne MEOSS line scanner imagery with good success. In the bundle adjustment a refined mathematical model of the interior and exterior orientation takes into account the specific MOMS-02 geometry. After describing the derivation and characteristics of the input data the functional model is briefly summarized. The results of the bundle adjustment, as compared against 43 independent check points, are presented and discussed. An empirical standard deviation of approximately 1 pixel (13.5 m) was obtained for each coordinate. Finally, the first experience with the MOMS-02/D2 data are concluded and an outlook towards the forthcoming MOMS-2P/PRIRODA mission onboard the Russian space station MIR, scheduled for early 1996, is given.

Mapping of erosion risk zones in the Lake Tana region of Ethiopia

The imaging mode 3 of the Modular Optoelectronic Multispectral Scanner (MOMS-02) combines two along-track panchromatic stereo bands (520 - 760 nm) with two multispectral bands in the red (645 - 680 nm) and near infrared (770 - 810 nm) wavelength spectrum. This special design offers the opportunity to combine the stereoscopic evaluation of relief parameters with thematic information on actual landuse from multispectral bands. Using FAOs Universal Soil Loss Equation (USLE) for a test site in the Ethiopian Highlands actual relief and thematic information is needed in order to derive an actual erosion risk map. MOMS-02 multispectral data was used as a data source for soil type mapping, the actual landcover and management intensity estimations. Potential natural vegetation cover and agroclimitical data were digitized from official large scale maps. Relief parameters like slope gradient and length were derived from a digital terrain model (DTM). DTMs were generated out of aerial photographs (1:50,000) and MOMS stereo data. They have been geocoded and validated by differential GPS measurements. Both DTMs were compared in order to show the potential of DTMs derived from MOMS. GIS based evaluations of the extracted parameters finally lead to an actual erosion risk map of the test site Dir Dira. Using landuse information from old topographic maps as an parameter for the USLE result in an historical erosion risk map. The comparison between both results shows a considerable increase of the endangered areas within 10 years.

Photogrammetric evaluation of MOMS-02 Mode 3 data (Mexico, Ethiopia)

The Modular Optoelectronic Multispectral Scanner (MOMS-02) has been flown successfully on the German space shuttle mission D2 in April/May 1993. Its outstanding feature is along- track stereoscopic imaging. The imaging mode 3 of MOMS is combining the two off-nadir panchromatic channels with two nadir-looking color channels (red and near infrared). The ground pixel size is 13.5 X 13.5 m2, and the base to height ratio is about 0.8. The paper reports on results of the photogrammetric evaluation of MOMS mode 3 data on Mexico (D2 orbit 82) and on Ethiopia (D2 orbit 61). The evaluation is subdivided into three major steps: (1) Automatic Imaging Matching to derive large numbers of conjugate points, performed with software which has been developed at DLR for the common Indian-German stereo scanner project MEOSS. The software has been successfully applied to MEOSS airborne imagery. (2) Combined Point Determination for the reconstruction of the exterior orientation and the calculation of the ground coordinates of a subset of conjugate points using the photogrammetric bundle adjustment software CLIC developed at Technical University Munich. For Ethiopia empirical accuracies of 23 m in X, 19 m in Y and 13 m in Z were obtained using 34 independent check points. Generation of a Digital Terrain Model from a dense network of conjugate points, which previously are transformed into object space by multiple forward intersection. For the Ethiopian example the conjugate point network was densified by additional image matching. The algorithm is based on the region growing approach, proposed by Otto and Chau. A report on the results achieved is given.