Potential for resurs DK-1 satellite data/Resurs DK-1 palydoviniu duomenu panaudojimo galimybe.

Ewiak, Ireneusz ; Kaczynski, Romuald

1. Russian satellite Resurs DK-1 system

Resurs DK-1 was designed by RASA (Russian Aviation Space Agency) in the frame of the National Space Programme of the Russian Federation (Anshakov and Skirmunt 2000). The main designer and producer of the satellite system Resurs DK-1 is State Research and Production Space Rocket Centre "TsSKB-Progress" (Fourni-er-Sicre et al. 2003). Resurs DK-1 with a Geoton RDK-1 camera was placed on the elliptical orbit with an inclination of 63[degrees] with an apogee and perigee of 585 km and 355 km respectively on June 15th, 2006 by the spacecraft Soyuz-U. The revisit time of this satellite is 6 days.

The acquisition of image data by Resurs DK-1 sensors is realized in panchromatic mode P (0.58-0.8 [micro]m) and multispectral mode (M) in three bands: M1 (0.5-0.6 [micro]m), M2 (0.6-0.7 [micro]m) and M3 (0.7-0.8 [micro]m) with a spectral resolution of 10 bit/pixel and with 1 m GSD for P and 2-3 m for M in swath width from 4.7 km to 28.3 km for the nominal scanning range of 450 km.

2. Description of the test data

Two panchromatic images with GSD about 1 m were tested. The first image covering 12 by 12 km is representing the centre of Warsaw. This image was taken on September 24th, 2006 using the Geoton RDK-1 camera with an inclination of 6.35[degrees] and a scan azimuth angle of 31.45[degrees]. The second one covering about 10 by 10 km of the North-West of Cracow was acquired on July 3rd, 2006. Sensor inclination of-nadir was 7.65[degrees] and a scan azimuth angle made about 30.76[degrees]. In both cases, the scenes were acquired with sun elevation of 37[degrees].

3. Geometrical correction of Resurs DK-1 images

The methodology of the geometrical correction of Resurs DK1 satellite images elaborated by the authors uses an adapted model of geometric reconstruction for IKONOS. However, in the case of new Russian satellite images, the main problem is the unavailability of the users to employ special "Z-Space" software used in Russia for the orientation of Resurs DK-1 data. Only files representing orbital parameters for each image and a set of not well defined coefficients have been available to the authors. These parameters have been used for elaborating algorithms for a geometric reconstruction of Resurs DK-1 images using Ortho Engine modules applied normally for the orientation of IKONOS data only.

The proprieties of the internal programming environment of the PCI Geomatica software have been used. The adaptation of the recorded structure of Resurs DK-1 metadata to the structure of RPC coefficients format and the structure of the orbital parameters of IKONOS system was the main task of the processed algorithms. The first algorithm relates to the geometric reconstruction of Resurs DK-1 images based on the rigorous mathematical model while the second one is based on the rational function model.

For two images of Resurs DK-1 from 24 to 28, well identified natural GCP's were measured applying GPS technique. The measurement of the image coordinates of the points was performed using the modules of Ortho Engine PCI Geomatica software v.10.3. The accuracy of the measurement and the identification of GCP's and ICP's should be better than 0.4 m in X, Y and 0.3 m in height. The examples of GCP's and ICP's are shown in Fig. 1.

Two mathematical modelling methods of the geometric reconstruction of Resurs DK-1 images have been used. The analysis of the influence of the number and the distribution of control points on each scene on the result of geometric reconstruction was realized in each method. The first method is the collinearity based mathematical model which describes the rigorous geometry of the scanner utilizing knowledge of satellite trajectory and sensor calibration data. This method integrates all components of viewing geometry and sensor as well as the Earth's parameters and cartographic projection. In this method, 5 to 12 well identified and distributed GCP's were measured. Accuracy has been checked with well defined ICP's (Table 1).

The model of geometric correction based on the first method is equivalent to the accuracy of about a half pixel of the source image. RMSE X = 0.45 m and RMSE Y = 0.46 m have been achieved on 16 ICP's. Using the orbital parameters of Resurs DK-1 satellite caused the limitation of measured GCP's required for geometric reconstruction. The results obtained in this method show the influence of real orbital satellite parameters on the mathematical model of the geometric reconstruction of Resurs DK-1 images. The result below one pixel of the source image is possible to be achieved when only 5 GCP's are used. If the number of GCP's is increased to 8, better results are achieved employing this method (see Table 1).

[FIGURE 1 OMITTED]

In the second method based on the rational function mathematical model of the geometric reconstruction of Resurs-DK-1 images, the unknown of the terrain related to Rational Polynomial Coefficients (RPC) were calculated on the basis of GCP's measured in the field and image. The correlation of the unknown RPC parameters depends on the number of GCP's, the accuracy of their identification in the field and image and their distribution on the image. RPC data have been estimated independently from a different number of control points. The results of geometric reconstruction are shown in Table 2.

The optimal degree of the polynomial for the estimation of the relationship between image and ground coordinates has been investigated. Using 18 GCP's allows calculating 9 polynomial coefficients. Increasing the number of control points up to 24 needed for a better determination of RPC gives the result of geometric correction RMSE X = 0.32 m and RMSE Y = 0.36 m. However, in this case, the necessity of measuring only 8 GCP's disqualifies the method of a terrain related RPC-solution. Accuracy below one pixel is guaranteed only if 10 control points evenly distributed in the scene are used.

Taking into account an economical aspect of geometrical reconstruction to reduce expensive field measurements of GCP's, it is recommended to use the first method. However, the final choice depends on an access to original orbital sensor data which is usually not the case. Additionally, when analyzing a' priori and a' posteriori errors at the ICP's, it was confirmed that this method was the most credible in the sense of correct results.

The geometrical reconstruction of Resurs DK-1 source images with the use of the method based on the independent determination of polynomial coefficients is well-founded. It was confirmed that to obtain similar RMSE at check points in the analyzed methods, 18 control points in the method based on RPC determination was required. This method could be used as an alternative in the case if access to the full metadata of the Resurs DK-1 image is impossible. DK-1 satellite data can be geometrically corrected up to a half pixel of the source image.

4. Requirements for the orthorectification process of Resurs DK-1 images

The influence of terrain height variation on the accuracy of orthoimages generated from the nadir satellite image is not that big as in case of aerial photographs in the small scale. Therefore, for the orthorectification of satellite images taken with small of-nadir viewing is possible to use DEM with less accuracy (Ewiak and Kaczyn-ski 2005). The accuracy of digital orthoimages depends on the accuracy of the geometrical correction of source Resurs DK-1 images and the accuracy of DEM.

For the purpose of generating orthoimage with the accuracy of a topographic map in the scale of 1:10,000, DEM from SRTM could be used. The following steps are needed to perform:

--geometrical correction using sensor orbital data, measuring a minimum of 5 ground control points and using DEM with accuracy better than 12 m for images acquired with a small of-nadir angle,

--geometrical correction of the source image with the determination of a minimum of 4 polynomial coefficients and the use of DEM with accuracy better than 6 m.

The influence of terrain height variations on the orthoimage of test areas is small. Therefore, Shuttle Radar Topographic Mission (SRTM) data have been analyzed. On the basis of a statistical analysis of SRTM data realized in the Institute of Geodesy and Cartography in Warsaw, it was confirmed that in the 90% area of Poland, the accuracy of height was about 2.9 m for flat and 5.4 m for hilly terrain (Karwel and Ewiak 2008). However, it has been found that SRTM data contains a systematic error component in height (Jacobsen 2006; Ewiak and Kaczynski 2008). After the elimination of component DEM, SRTM have been used for generating orthoimages from Resurs DK-1 images with the planimetric accuracy of 2.5 m required for the scale of 1:10,000.

5. Estimation of the accuracy of the orthorectification process of Resurs DK-1 source images

The accuracy of orthoimages has been achieved on the basis of differences calculated from coordinates on orthoimages and measuring reference ground position in the field. Accuracy achieved employing the above introduced methods was calculated on 18 ICP's for Cracow test area and 23 for Warsaw test area. In the orthorectification process, the corrected SRTM data set with the accuracy of [+ or -] 1.1 m for Cracow test area and [+ or -] 0.8 m for Warsaw test area were used (Karwel and Ewiak 2008). The results of the orthoimages generated with 1m pixel size are shown in Table 3. For all used orientation methods, the obtained orthoimage accuracy corresponds to the required accuracy of the base map in the scale of 1:10,000. The accuracy of orientation based on the rigorous mathematical model of the satellite sensor of Resurs DK-1 corresponds to the accuracy of the base map in the scale of 1:5,000. It has been found that the accuracy of orthoimages generated with 50cm pixel size is only imperceptibly higher.

The best quality of the orthorectification process of Resurs DK-1 images requires a large number of GCP's for the calculation of RPC coefficients. The economical aspect of the geometric reconstruction of Resurs DK-1 scenes showed the necessity of using the original polynomial coefficients provided by the satellite imagery vendor and computed from the rigorous sensor model.

6. Comparision of handling Resurs DK-1 and IKONOS-2 data

The analysis was related to the technical and economic aspects of the generation of digital orthoimages with accuracy required for maps in the scale of 1:10,000. The orthoimages have been generated based on images for the test areas:

--a panchromatic image of IKONOS and that of Resurs DK-1 covering the first test area (121 square kilometres) situated in the centre of Warsaw with flat terrain,

--a panchromatic image of Resurs DK-1 covering the second test area (100 square kilometres) situated in the North--West part of Cracow with hilly terrain.

[FIGURE 2 OMITTED]

Better results of the panchromatic scene of IKONOS have been achieved due to the higher precision of RPC supplied by GeoEye and higher internal accuracy of the pixels in the IKONOS image (Kaczynski and Ewiak 2005). The accuracy of geometrical correction in all methods of Resurs DK-1 images met the standards for topographic maps in 1:10,000 and smaller scales. A sample of orthoimages is shown in Fig. 2.

The small off-nadir viewing angles of the sensor have caused that the geometric dislocation of the orthoimages are mainly affected by the scene orientation of the source image data. DEM with accuracy about 4 m is sufficient for the orthorectification images taken with small of-nadir collection for IKONOS and Resurs DK-1. The source of such DEM to be used for both types of images could be a corrected set of SRTM data.

The reason of applying the given type of satellite image can be only the cost of the source satellite scene. The price of the programmed scene of Resurs DK-1 for one square kilometre is 9.5 EUR for a panchromatic image. The price of the archive scenes of Resurs DK-1 is reduced to 8 EUR. The Geoinformation Agency "Innoter" from Moscow is the main distributor of Resurs-DK-1 image data.

The price of one square kilometre of the IKONOS panchromatic image is about 18 EUR Resurs DK-1 images, if would be easy available to the users, could be used for mapping and updating topographic maps up to the scale of 1:10,000.

7. Conclusions

The high resolution Russian satellite images of Resurs DK-1 could be used for generating orthoimages in the scale of 1:10,000. The accuracy of geometric reconstruction depends on the method used taking into account the rigorous mathematical sensor model and terrain related RPC coefficients as well as the number and distribution of well identified GCP's.

The transformation of the image to the ground coordinate system can be performed with accuracy better than half a pixel for Resurs DK-1 image and IKONOS satellite systems. Geometric accuracy for Resurs DK-1 images is about 0.5 m. The accuracy of DEM required for orthorectification depends on the of-nadir acquisition of raw images.

DEM with the accuracy of the height of about [+ or -] 4 m could be used for the rectification process of Resurs DK-1 with a small of-nadir angle and flat area. Orthoimages can be generated from DK-1 and IKONOS with accuracy corresponding to the geometric standards in Polish maps in the scale of 1:5,000 but the information contents of these images refer to the scale of 1:10,000.

doi: 10.3846/gc.2010.07

Received 10 03 2010, accepted 01 04 2010

References

Anshakov, G. P. and Skirmunt, V. K. 2000. The Russian Project of Resurs DK-1 Space Complex Development. Status, Prospects, New Opportunities for the Consumers of Space Snapshots, Acta Astronautica 47(2): 347-353. doi:10.1016/S00945765(00)00076-X

Ewiak, I. and Kaczynski, R. 2005. Correction of IKONOS and QuickBird data for orthophotomaps generation, in Proceedings of the 26th Asian Conference on Remote Sensing, 7-11 November 2005, Hanoi, Vietnam.

Ewiak, I. and Kaczynski, R. 2008. SRTM data used for orthorectification of IKONOS and QuickBird images, in Proceedings of the Seminar "The cartographical elaboration of the cadastral maps of the agricultural regions on the basis of satellite images", 22 September 2008, Dushanbe, Tajikistan.

Fournier-Sicre, A.; Suslova, T. and Krasnov, A. 2003. Resurs DK-1 Visual and IR-band imaging at 1m resolution, ESA "News from Moscow", Special Issue 9: 11-14.

Jacobsen, K. 2006. SRTM height models, Geoconnexion International Magazine August: 20-21.

Kaczynski, R. and Ewiak, I. 2005. Accuracy of orientation of QuickBird and ortho generation in urban areas, in Proceedings of the Euroimage Meeting, 20-21 October 2005, Eventi Conference Center, Roma, Italy.

Karwel, K. and Ewiak, I. 2008. Estimation of the accuracy of the SRTM terrain model on the area of Poland, in Proceedings of the XXIISPRS Congress, 3-11 July 2008, Beijing, China, XXXVII, Part B7: 169-172.

Romuald KACZYNSKI is a professor in the Military University of Technology (WAT) in Warsaw, Poland. He worked 33 years in the Institute of Geodesy and Cartography in Warsaw in modern Photogrammetry and Remote Sensing methods and technologies. He was V-ce President of Polish Society for Photogrammetry and Remote Sensing. He worked in the IN-TERCOSMOS programme and as UNDP expert in Vietnam, Ethiopia and India. He has received prestige Dolezal Award by ISPRS Congress in Vienna 1996. Now he is International Team Leader and Key expert No 1 in Photogrammetry and Satellite Image Processing in the European Commission funded project in Tajikistan.

Ireneusz EWIAK. Doctor Eng. Institute of Geodesy and Cartography. Department of Photogrammetry, Modzelewskiego 27, 02-697 Warsaw, Poland. (Ph +48 022 3291985, Fax +48 022 3291950), e-mail: rene@igik.edu.pl

A graduate of Warsaw University of Technology (Master of science, 1992). PhD degree since 2004 from Institute of Geodesy and Cartography in Warsaw.

Author and co-author of more than 30 scientific papers published abroad and presented on the national and international conferences (ISPRS, ASPRS, ACRS). Visiting scientist in Photogrammetry and Remote Sensing in: University of Liege in Belgium, Chinese Academy of Surveying and Mapping in Beijing, University of Stuttgart in Germany, Fazo Institute in Tajikistan.

Lecturer in digital processing of satellite data and digital photogrammetry in Warsaw University and Military University of Technology in Warsaw.

Research interests: satellite and video photogrammetry, digital aerial photogrammetry and mobile laser scanning for 3D mapping.

Ireneusz Ewiak (1), Romuald Kaczynski (2)

(1) Institute of Geodesy and Cartography, Warsaw, Poland

E-mail: rene@igik.edu.pl

(2) Military University of Technology, Warsaw, Poland

E-mail: rkaczynski@wat.edu.pl

Table 1. The results of the geometric reconstruction of Resurs
DK-1 images applying the 1st method

 RMSE at the ICP's [meters]
 Number of Number of
 GCP's for ICP's for Warsaw test area Cracow test area
 test areas test areas
Warsaw/Cracow Warsaw/Cracow X Y X Y

 12 16/12 0.44 0.46 0.44 0.46
 10 18/14 0.45 0.47 0.46 0.44
 8 20/16 0.46 0.48 0.45 0.46
 6 22/18 0.53 0.48 0.57 0.53
 5 23/19 0.73 0.82 0.84 0.92

Table 2. The results of the geometric reconstruction of Resurs
DK-1 images applying the 2nd method

 Number
 of ICP's RMSE at the ICP's [meters]
 for test
 areas Number of Warsaw test area Cracow test area
 Number Warsaw/ polynomial
of GCP's Cracow coefficients X Y X Y

 24 4/0 12 0.32 0.36 0.37 0.36
 22 6/2 11 0.34 0.32 0.36 0.38
 20 8/4 10 0.40 0.38 0.39 0.38
 18 10/6 9 0.45 0.45 0.41 0.44
 16 12/8 8 0.52 0.46 0.48 0.45
 14 14/10 7 0.58 0.62 0.49 0.55
 12 16/12 6 0.76 0.82 0.69 0.71
 10 18/14 5 0.82 0.90 0.88 0.97
 8 20/16 4 1.04 1.18 1.22 1.34

Table 3. The accuracy of the geometric correction of Resurs DK-1 images

 RMSE XY [m]
 Characteristic of geometrical
 reconstruction methods of Warsaw Cracow
 Resurs DK-1 images test area test area

QUALITY ASPECT

Rigorous model with 8 GCPs 0.62 0.61
Polynomial coefficients calculated
 on the basis of 24 GCPs 0.56 0.61

ECONOMICAL ASPECT (if less GCPs are used)

Rigorous model with measured of 5 GCPs 1.12 1.23
Polynomial coefficients calculated on
 the basis of 12 GCPs 1.66 1.87