1. Test Ranges for Metric Calibration and Validation of Satellite Imaging Systems  Gene Dial (gdial@spaceimaging.com)  Jacek Grodecki (jgrodecki@spaceimaging.com)

2. © 2003 Space Imaging, LLC. Confidential and proprietary. Topics  IKONOS Introduction  Importance of Clear Skies  Preflight test ranges Requirements Validation  Post Launch Test Ranges Recalibration Accuracy Test & Monitoring  Ground Control Points Good & Bad Image Display Effects High Quality  Summary & Conclusions

3. © 2003 Space Imaging, LLC. Confidential and proprietary. IKONOS Satellite Use Simultaneous Pan and Multispectral images Panchromatic pixels: 0.82 m at nadir Multispectral pixels: 3.28 m at nadir (Blue, Green, Red, NIR) Linear detector arrays scan in any direction Swath width: 10.8 km at nadir Image Specifications Use 680-km near-polar, sun-synchronous orbit. 3-day revist with elevation > 60° 25 m CE90 accuracy without GCP 2 m CE90 accuracy with GCP Same pass stereo strips up to 400 km long 25 m CE90 horizontal, accuracy 22 m LE90 vertical accuracy Metric Specifications

4. © 2003 Space Imaging, LLC. Confidential and proprietary. Select Low-Cloud Areas for Test Ranges Gene Dial, SIE, 4/5/97

5. © 2003 Space Imaging, LLC. Confidential and proprietary. Northern Test Range  Purpose: Verify Requirements  Size: 20 km NS x 30 km EW  GCP: 140 cultural features  Accuracy: 0.5 m CE90, 0.9 m LE90  Source: Large-scale aerial photography  Imagery: “San Diego Seven” Stereo triplet on the West Stereo pairs center and East Supplied to SW developers for test  Results: IKONOS meets requirements. Without Ground Control – 25 m CE90 horizontal – 22 m LE90 vertical With Ground Control – 2 m CE90 horizontal – 3 m LE90 vertical

6. © 2003 Space Imaging, LLC. Confidential and proprietary. Southern Test Range  200 GCP in 100 km x 100 km area  Differential GPS Survey  NS line for exterior orientation  EW line for interior orientation  Many points difficult to identify Chip at lower right shows 1 m by 2 m black rectangle on 1 m diameter white water pipe

7. © 2003 Space Imaging, LLC. Confidential and proprietary. Interior & Exterior Orientation

8. © 2003 Space Imaging, LLC. Confidential and proprietary. Case Study: 6 Stereo Pair, 60 GCP 190000010105274 2001032518295100000010105276 50510Miles N EW S  Processed with one GCP.  Remaining GCP test accuracy.

9. © 2003 Space Imaging, LLC. Confidential and proprietary. Original Field Angle Map, 1 GCP CE90 = 8.6 m  Project Area 6 Stereo Pair Wide Precision GCP  Residual Error Pattern All residuals point to GCP Suggestive of scale error About 2 m per strip  Corrective Action Denver test range for FAM calibration Interior orientation adjusted Scale Error Removed

10. © 2003 Space Imaging, LLC. Confidential and proprietary. Calibration of Interior Orientation

11. © 2003 Space Imaging, LLC. Confidential and proprietary. After FAM Recalibration of Nov 19, 2001. CE90 = 1.8 m

12. © 2003 Space Imaging, LLC. Confidential and proprietary. Exterior Orientation Repeated acquisitions of MTF target Target surveyed by differential GPS Median error measured Interlock angles adjusted to zero median error. Initialization

13. © 2003 Space Imaging, LLC. Confidential and proprietary. Repeated Acquisitions to Verify Interlock Angles

14. © 2003 Space Imaging, LLC. Confidential and proprietary. Ad-hoc Tests of System Accuracy  Procedure Acquire GCP for Precision orders Process Imagery without GCP Evaluate Errors  Example 49 check points 24 stereo pairs  Reference: Dial, IKONOS Stereo Accuracy, ASPRS 2003.  GCP: Cultural Features Range-only differential 1 m CE90, 2 m LE90.  Result: IKONOS Stereo Accuracy 6 m CE90 Horizontal 10 m LE90 Vertical

15. © 2003 Space Imaging, LLC. Confidential and proprietary. Repeatability  Results of 5 trials with 1 operator Range = 0.375 pix Sigma = 0.16 pix  Operator variation could be significant

16. © 2003 Space Imaging, LLC. Confidential and proprietary. Effect of Resampling and Contrast on Corner Position Change from NN to CC resampling moves apparent corner position by 0.25 pixels

17. © 2003 Space Imaging, LLC. Confidential and proprietary. Contrast: Low vs. High

18. © 2003 Space Imaging, LLC. Confidential and proprietary. Brightness: Light & Dark

19. © 2003 Space Imaging, LLC. Confidential and proprietary. Effect of Resampling, Brightness, & Contrast  Resampling effect is in the noise level. Contrast changes had no effect on perceived position.  Brightness changes had a significant effect Bright images – Lower contrast to white square – Increase contrast to black square – Operator picks further away from black corner Dark images have converse effects  Ideal GCP are centerline, not corner features.

20. © 2003 Space Imaging, LLC. Confidential and proprietary. Examples of Good Ground Control  Good Ground Control Points Intersection of Cross-Walk and Stop Lines Sidewalk intersection Home plate at baseball field Intersection of Service Line and Center Line of a Tennis Court – Intersection of Side Lines with Base Line is not good.

21. © 2003 Space Imaging, LLC. Confidential and proprietary. Examples of Poor Ground Control  Examples of Poor GCP Locations Dirt Road Intersection Acute road intersection Walled compounds

22. © 2003 Space Imaging, LLC. Confidential and proprietary. GCP Panels for IKONOS  GCP Panels for IKONOS “Tyvek” panels Aligned North-South. Control point is center square  Lessons Learned Tests with 3 observers agreed within 0.05 m RMS. Narrow gap sometimes hard to see End panels unnecessarily large – Hard to deploy – Too bright See revised design at right  References Dennis Helder, Michael Coan, & Peter Gaska, “IKONOS Geometric Characterization” RSE 2003. Michael Coan, telecon & email. Original Revised

23. © 2003 Space Imaging, LLC. Confidential and proprietary. Multi-Point Measurements Reduce GCP Pick Error  Multiple Point Measurements Average errors of individual points. Symmetric distribution eliminates bias at contrast edge. Accuracy ~ 0.2 pixels  Reference C.S.Fraser, H.B.Hanley & T.Yamakawa, “Sub-metre Geopositioning with IKONOS Geo Imagery, ISPRS Joint Workshop “High Resolution Mapping from Space 2001”, Hanover, Germany 19-21 September

24. © 2003 Space Imaging, LLC. Confidential and proprietary. Summary & Conclusions  Metric Test Range Applications Requirements Verification Calibration of Interior & Exterior Orientation Verification of System Accuracy Monitoring of System Accuracy  Test Range Considerations High probability of cloud-free skies Availability of geodetic control Overall size suitable for sensor Cultural features suitable for ground control  Ground Control Points Use centerline, not corner features For ultimate accuracy – Deploy panels or use multi-point measurements  Thank you.