Radar Prism Displacement Comparison Tool
Cross-checks a slope-stability radar (SSR) displacement against a survey-prism displacement for the same point and period, returning the difference, percent difference and an agree/disagree verdict against your tolerance. Used by mine geotechnical teams to validate two independent monitoring systems.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the radar (SSR) displacement and the survey-prism displacement for the same point and time window (mm).
- Optionally set the agreement tolerance in mm (default 5).
- Read the difference, percent difference and verdict — investigate any pair that exceeds tolerance.
How it works
The difference is radar − prism, and the absolute difference is compared to the tolerance: within tolerance the two systems agree, beyond it they disagree. Percent difference is the difference as a percentage of the prism displacement.
Some difference is expected by design. Radar measures displacement along its line-of-sight (a single radial direction), while a prism measures the full three-dimensional vector, so the two only coincide when movement is aligned with the radar beam. This is a sanity/validation check, not calibration.
Worked example
SSR vs prism agree within 5 mm. Radar reads 25 mm and the prism reads 22 mm. Difference = +3 mm; percent difference = 3 ÷ 22 × 100 = 13.6 %. With a 5 mm tolerance, |3| ≤ 5, so the verdict is Agree — within tolerance.
Common mistakes
- Comparing different time windows or points — both systems must reference the same point and period.
- Expecting an exact match: line-of-sight radar and 3-D prism vectors legitimately differ.
- Setting an unrealistically tight tolerance that flags normal geometric differences as disagreements.
Frequently asked questions
Why don't radar and prism displacements match exactly?
Radar measures movement along its line-of-sight; a prism measures the full 3-D vector. Unless movement is aligned with the beam, the magnitudes differ even when both instruments work correctly.
What tolerance should I use?
The default is 5 mm, which suits many pit setups, but set it from your own accuracy budget and geometry.
What does a 'Disagree' verdict mean I should do?
It flags a difference beyond your tolerance. Investigate causes — atmospheric correction, prism disturbance, radar geometry or an actual localised movement — before trusting either value.
How is percent difference calculated?
(radar − prism) ÷ prism × 100. If the prism displacement is zero it is left as n/a because the division is undefined.
Is this a calibration tool?
No. It is a sanity/validation cross-check between two independent systems, not a means of calibrating one against the other.
Related tools
- Crack Displacement Calculator
- Prism Movement Rate Calculator
- Prism Movement TARP Checker
- Piezometer Trend Calculator
- Cumulative Movement Calculator
- Rolling Average Movement Calculator
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Tip: Enter any known values to calculate the remaining results.
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