Practical results of MOMS-02 r r

4. Practical results of MOMS-02 r r

r r r D2 image ori- entation This section describes the orientation of MOMS- 02rD2 imagery based on the orientation point ap- proach. Four image scenes a15 to a18 of the D2 Ž . orbit a75b nomenclature of DARA, 1994 were selected, covering an approximately 37 = 430 km wide area in Northern Australia. Besides several tie points, calibration data, navigation data and 64 ground control and check points are considered as additional information in a combined adjustment. During the last 2 years the Australian MOMS- 02rD2 data set was also evaluated by other research Ž . groups in Zurich Baltsavias and Stallmann, 1996 , Ž . Ž Melbourne Fraser and Shao, 1996 , Munich Dorrer . et al., 1995 and Glasgow. The four groups used different input data sets and different mathematical models. Most of the point determination results, however, fit in quite well with the results described in this paper. 4.1. Input data The image coordinates of tie points were derived automatically by a modified region-growing match- Ž . ing algorithm Otto and Chau, 1989 , which was Ž applied successfully in the past to SPOT Heipke and . Ž Kornus, 1991 and airborne MEOSS imagery Heipke . et al., 1996 . From this information a sparse and a dense subset of regularly distributed points were selected to be fed into the adjustment. According to experiences of the former evaluations, a standard deviation of 0.3 pixel for the image coordinates was assumed. The calibration data were provided by the Ger- Ž . man aerospace company DASA former MBB , the Ž . manufacturer of MOMS-02 DASA, 1994 . Correc- tion tables describe deviations of certain CCD pixels Ž . 500 pixel distance from their nominal positions in the image plane. The functional model of the interior orientation employs 9 parameters per lens or per Ž . channel, as described in Ebner et al., 1994 . A 10th parameter, modelling a second order sensor curva- ture, was added, since band-to-band registration of the first MOMS-2PrPRIRODA imagery yielded sys- tematic non-linear deviations from the calibration Ž . data of the multispectral channels Kornus, 1996 . In order to compensate for possible deviations of the stereo channels, the lab-calibrated parameters of the interior orientation were introduced with low weight into the adjustment allowing for the simultaneous estimation of deviations, at least to some extent. The naÕigation data were provided by NASA and Ž . processed by Geo-Forschungs-Zentrum GFZ Pots- dam. The orbit positions were compiled from TDRSS Doppler measurements, which were fed as observa- tions into the orbit determination software of GFZ Ž . Potsdam Braun and Reigber, 1994 , yielding a rela- tive orbit accuracy of 3 m and an absolute accuracy Ž . Ž . Ž . of 14 m radial , 32 m lateral and 31 m tangential . The gyro data were already preprocessed by NASA and provided as a time series of Euler angles at 1 s time interval with a relative accuracy of 20 Y . Since the alignment between the MOMS camera axes and the gyro axes was not calibrated, there is no absolute pointing knowledge. Both Euler angles and orbit positions were transformed into a local topocentric coordinate system with fundamental point at f s 21830 X S, l s 136800 X W, h s 300.0 m. Based on ap- proximation tests 8 orientation points were selected, having a distance of 4612 rows between each other. Seventy-seven ground control points GCP were measured by Melbourne University using differential Ž . GPS Fraser et al., 1996 . The points are located in a 37 = 100 km wide flat desert area covered by image scene a17. Most of the targets represent road junc- tions or dams of artificial water basins, which could be identified in the imagery with about 1 pixel precision. At ETH Zurich 68 GCP were measured in Ž . the channel ST6 imagery forward and automati- Ž . cally transferred to channel ST7 aft . At DLR 49 of Ž . these points were transferred to channel HR5 nadir from both ST6 and ST7 imagery. From the differ- ences in HR5 a standard deviation of 0.4 pixel for the GCP image coordinates was derived. For the GCP object coordinates s s 1 m was chosen in Ž . height and s s 13.5 m 1 pixel in planimetry, due to the identification uncertainties. 4.2. Results First adjustment runs using 4 GCP yielded incon- sistencies in the input data: An 11.4 km bias of the orbit positions in flight direction was interpreted as a time mismatch between position data and image line Fig. 3. Configuration of control and check points. recordings in the order of 1.6 s. Further adjustment runs using all GCP led to the rejection of 4 GCP due to large planimetric residuals. From the remaining 64 Ž . GCP root-mean-square rms residuals of 9 m in X, 8 m in Y and 0.1 m in Z were obtained. The Z component is quite small due to the high weighting Ž . of the GCP Z coordinates s s 1 m compared to the weighting of the corresponding image coordinates Ž . s s 0.4 pixel . The planimetric residuals of nearly 10 m reflect the identification uncertainty mentioned above. In a series of adjustment runs using subsets of 4, 10 and 20 GCP, empirical accuracies were derived from the remaining 44 points, which served as inde- Ž . pendent check points see Fig. 3 . The Tables 2 and 3 contain the empirical accura- Ž . cies rms values computed for the different GCP configurations and sets of tie points using all naviga- Ž . Ž . tion data Table 2 and orbit data only Table 3 . The comparison between Tables 2 and 3 shows no significant differences in the results, indicating that attitude information is not required. From Tables 2 and 3 it can be seen that the results are only slightly improved if 1000 instead of 100 tie points are used. Despite of the given uncertainties, a height accuracy of up to 4.1 m is obtained, corresponding to 0.3 of the ground pixel size of the oblique looking channels Table 2 Ž . Empirical accuracies rms values ´ using all navigation data 1000 tie points 100 tie points 4 GCP 10 GCP 20 GCP 4 GCP 10 GCP 20 GCP w x ´ m 11.6 10.8 10.3 11.6 11.0 10.1 X w x ´ m 12.8 9.3 8.9 12.8 9.7 9.4 Y w x ´ m 4.1 4.6 4.3 5.3 4.9 4.7 Z Table 3 Ž . Empirical accuracies rms values ´ using orbit data only 1000 tie points 100 tie points 4 GCP 10 GCP 20 GCP 4 GCP 10 GCP 20 GCP w x ´ m 10.8 10.5 10.0 11.4 10.6 9.5 X w x ´ m 12.6 9.8 9.3 13.9 10.0 9.4 Y w x ´ m 4.1 4.5 4.3 5.2 4.6 4.6 Z Ž . 13.5 m . The planimetric accuracy potential of MOMS-02rD2 is not verified, since the GCP and check points could not be identified in the imagery with the required accuracy.

5. Computer