Test Ranges for Metric Calibration and Validation of Satellite Imaging Systems

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Test Ranges for Metric Calibration and Validation
of Satellite Imaging Systems

• Gene Dial (gdial_at_spaceimaging.com)
• Jacek Grodecki (jgrodecki_at_spaceimaging.com)

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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

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IKONOS Satellite
Image Specifications
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

Metric Specifications

• 680-km near-polar, sun-synchronous orbit.
• 3-day revist with elevation gt 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

Use
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Select Low-Cloud Areas for Test Ranges
Gene Dial, SIE, 4/5/97
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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

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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

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Interior Exterior Orientation
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Case Study 6 Stereo Pair, 60 GCP

• Processed with one GCP.
• Remaining GCP test accuracy.

N
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Original Field Angle Map, 1 GCP

• 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 forFAM calibration
• Interior orientationadjusted
• Scale Error Removed

CE90 8.6 m
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Calibration of Interior Orientation
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After FAM Recalibration of Nov 19, 2001.
CE90 1.8 m
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Exterior Orientation

• Repeated acquisitions of MTF target
• Target surveyed by differential GPS
• Median error measured
• Interlock angles adjusted to zero median error.

Initialization
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Repeated Acquisitions to Verify Interlock Angles
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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

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Repeatability

• Results of 5 trials with 1 operator
• Range 0.375 pix
• Sigma 0.16 pix
• Operator variation could be significant

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Effect of Resampling and Contrast on Corner
Position
Change from NN to CC resampling moves apparent
corner position by 0.25 pixels
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Contrast Low vs. High
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Brightness Light Dark
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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.

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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.

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Examples of Poor Ground Control

• Examples of Poor GCP Locations
• Dirt Road Intersection
• Acute road intersection
• Walled compounds

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GCP Panels for IKONOS
Revised

• 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
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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

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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.