Apr 24, 2013

Comparing geometric properties of TH-01-1 and SPOT 5 data

Estimated Article Reading Time: 2 min.

ScanEx RDC specialists carried out testing of data, received from TH-01-1 satellite (China), and compared it with the French SPOT program data. Satellite images, acquired by TH-01 imaging system, are of great interest for users and basically challenge the data, acquired by the European SPOT program, which is currently represented by the SPOT 5 and SPOT 6 satellites.

Within the frames of the proposal about partnership relations between BSEI (China) and ScanEx RDC (Russia) companies several samples of the test data from TH-01-1 satellite of 1A and 1B levels were provided to the Russian specialists. The information obtained by GFB, DGP and SXZ cameras was integrated into this test data. For comparison the SPOT image was taken, acquired on September 2012 and received by one of the ground stations of ScanEx’s network and the TH-01-1 image, acquired on April 26, 2012. The scheme of TH-01-1 and SPOT 5 images overlay is shown on Fig. 1. Test data cover the area on the border of Kemerovo Region and the Republic of Khakassia, located between 55°42` – 56°17`N and 88°8` – 89°5`E.

The assessment of geometric properties of TH-01-1 data of 1A and 1B level was given during the testing, as well as comparison was made with the results of similar activities, carried out using SPOT 5 Level-1A data.Panchromatic images, received by GFB camera (TH-01-1 satellite) with the GSD of 2 m, and pan images, received by HRG camera (SPOT 5) with the GSD of 2.5 m were selected.

For each image the measurments at 16 control points were performed. The ortho-rectified coverage of the territory with very high resolution images from GeoEye-1 was used as the source of planned coordinates, whereas SRTM matrix was used as the elevation source. Control points location layout is shown on Fig.2 and 3.

— Rational polynomial coefficients (RPC) of the third order are supplied with TH-01-1 products, being the approximation of a strict model of the imaging equipment. SPOT 5 data does have RPCs. A strict approach, enabling to do tracking of beams, forming the image, and to find their intersection with the ground, using data about satellite trajectory, is required for their photogrammetric processing. All the required information is stored in the DIM metadata file, being part of the delivery package, – explains Anton Sonyushkin, Head of the Image Processing and Software Development Department of ScanEx RDC.

Several experiments based on using some types of transformations were done to assess the images orientation accuracy for correction, both RPC and strict model at different correlation of control and reference points.

According to performed measurements, the nominal accuracy (within control points) of GFB Level-1A (TH-01-1) products was 333.5 m of RMS and 715.8 m per CE90% criteria, which does not match the announced accuracy of 25 m per CE90%. Besides, according to experiments, the maximum accuracy of GFB Level-1A products transformation was 23 meters RMS and 49.9 CE90% and was obtained when using projective corrections at 16 control points. No considerable changes in the accuracy with the reduction in control points’ number could be therewith registered. This enables to come to the conclusion about considerable inaccuracy of the GFB camera strict model (TH-01-1) used to calculate the RPC for Level-1A products.

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