Test Ranges for Metric Calibration and Validation of Satellite Imaging Systems  Gene Dial  Jacek Grodecki

© 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

© 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

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

© 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

© 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

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

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

© 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

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

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

© 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

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

© 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  GCP: Cultural Features Range-only differential 1 m CE90, 2 m LE90.  Result: IKONOS Stereo Accuracy 6 m CE90 Horizontal 10 m LE90 Vertical

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

© 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

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

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

© 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.

© 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.

© 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

© 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 Michael Coan, telecon & . Original Revised

© 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 September

© 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.