ms.02 new understanding ssr data

Understanding and Analysis of Understanding and Analysis of

Slope Stability Radar DataSlope Stability Radar DataMine Services

Commercial in Confidence

Cerro Verde SSR Training

Jan/2011

SSR Output (Basic)SSR Output (Basic)

Deformation

The measure of phase change (velocity) between

scans

Amplitude

Magnitude of resultant vector of phase return

Range

Select one range bin that is potentially covering a

pixel 15 by 15 metres (more in long range)



Jan/2011

Deformation (is weighted by amplitude)Deformation (is weighted by amplitude)

Amplitude=53.91

Deformation=12.93mm

Range=436.34m

Coherence=0.95



Jan/2011

Deformation of rock wall, less than 1.0mm

Effect of the drill mast on deformation, amplitude and range



Jan/2011

Amplitude Amplitude High Amplitude from Truck ReflectionHigh Amplitude from Truck Reflection

Truck

Truck



Jan/2011

Amplitude High Amplitude from Truck Reflection

No Truck

No Truck

Amplitude Amplitude High Amplitude from Truck ReflectionHigh Amplitude from Truck Reflection



Jan/2011

Use Single Scan to Review Effect on DeformationUse Single Scan to Review Effect on Deformation

Noise introduced in

the deformation

image by the truck

Noise introduced

in the deformation

plot by the truck



Jan/2011

Constant range



Jan/2011

Range IssuesRange Issues

At long range (using current system) range

wrapping occurs

At short ranges strange reflection paths,

particularly in built up environments

Range bins can often changes during rain

because the most favourable target changes

(surface water running over wall changes energy

return)



Jan/2011

SSR OutputSSR Output

Delta Amplitude Measure of maximum change of amplitude between the two time sliders

Delta Range Measure of maximum change of range between the two time sliders

Coherence Coherence time is the time over which a propagating wave may be considered coherent. In other words, it is the time interval within which its phase is, on average, predictable



Jan/2011

Delta RangeDelta Range

Delta range



Jan/2011

Delta AmplitudeDelta Amplitude

Delta amplitude



Jan/2011

SSR Control Output (for each pixel)SSR Control Output (for each pixel)

Scan 1

Scan 2

COHERENCE

1.00

Scan 3

Rockfall

0.82

Scan 4

Collapse

0. 21

Range

Amplitude



Jan/2011

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Deformation

Coherence

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Rain accumulation

Coherence

Collapse caused by several

events of rain. Low coherence

during the development of the

collapse, and some correlation

between rain and subsequent

deformation.

Rain accumulation



Jan/2011

Coherence Measure of RillingCoherence Measure of Rilling



Jan/2011

Coherence Measure of SnowCoherence Measure of Snow



Jan/2011

Coherence Measure of PipeCoherence Measure of Pipe



Jan/2011

FiguresFigures

Select figures with care

Avoid trucks & vegetation

Remove run-away pixels

from the figure

Avoid potential artificial

effects (drill masts)

Assess any misalignment

between the camera and

SSR

Deformation plot

without machinery

noise

Deformation plot with

machinery noise,

totally unrealistic.



Jan/2011

Correction TabCorrection Tab

Very useful to review data in a quick manner

Check that system is performing well

Useful to see atmospheric correction effects on deformation

Usually can determine poor set up conditions

Time per scan!!!!



Jan/2011

Time SlidersTime Sliders



Jan/2011

SSR Data : The big issuesSSR Data : The big issues

1. Phase Ambiguity : runaway pixels

2. Extreme Atmospherics

3. Pixel size and minimum wall area

1 and 2 are often related!



Jan/2011

Phase AmbiguityPhase Ambiguity

When wall movements greater than 15mm occur between scans (approximately 180 mm/hr @ 12 min scans). The software attempts to correct for this ambiguity, however there is a risk that the software misinterprets the movements and causes an error.

The software attempts to solve this problem by tracking the velocity of each point on the wall. It then predicts the next point in time using this predicated velocity. The measured phase is then used to determine the movement near to this predicted point. The predicted velocity is calculated using the history ofprevious points. This allows differentiating gradual wall movements from sudden changes due to trucks.

The problem with this technique however, is that when a wall is accelerating, the predicated velocity will lag the true velocity. This can result in a mistake with the velocity estimate. This mistake will add 15 mm to every subsequent scan, until SSRControl software on the radar is manually restarted.



Jan/2011

Characteristic large

positive or negative

values

Ambiguity during fast deformationAmbiguity during fast deformation



Jan/2011

Extreme AtmosphericsExtreme Atmospherics

Changes in refractive index are corrected by the SSR system using a direct measurement technique. This requires the user to select a wall area (called the atmospheric correction region) within the scan area that the geologist knows to be stationary. Each time the system scans the wall, it uses the movement in this region in conjunction with its range to calculate the refractive index in ppm. It then uses the ppm and the range to each pixel on the wall to correct for atmospheric variations from one scan to the next.

However, if an extreme weather front comes through the scan area, it can suddenly change the atmospheric conditions within a single scan. This results in the section above the atmospheric correction region being corrected differently to the section below the atmosphericcorrection region. This effect is more evident with long scan intervals where the atmospheric variation can be greater between scans.

If alarms are set when this phenomenon occurs, the alarms are likely to be triggered.



Jan/2011

Pixel Size and Minimum Pixel Size and Minimum

Wall Movement AreaWall Movement Area

The Slope Stability Radar (SSR) is a very effective slope monitoring system for both small and large areas of instability. However, wall movements over small areas compared with the pixel size cannot be measured accurately.

The dish forms the radar waves into a pencil beam with a diameter of about 2.5 degrees. The area illuminated by the radar beam on the wall is called the footprint

The figure to the right shows nine pixels of a radar image, with thecentral pixel highlighted.The shaded greycircle indicates thecorresponding radar footprint.

Note the footprint perimeter is fuzzy rather than sharp and the footprint is considerably larger than a pixel.



Jan/2011



Jan/2011

Pixel Size and Small FailuresPixel Size and Small Failures

It is quite likely that for a large rock boulder to move that the surrounding muckpile/rockmass would also deform/displace and we would record some deformation, however I (GroundProbe) cannot be certain that this is the case and we might not get enough early warning of movement.

I suggest positioning the SSR close enough so the boulder is covered by 2+ pixels or use another risk management technique to deal with these boulders (with confidence). For a 2 by 2 m boulder, to achieve the requisite distances: an SSR would have to be within 75-100m of the face and an SSR-X around 150-200m.



Jan/2011

SSR System

Shading is the size of the radar beam

The red bock is the minimum size of failure that can be detected

SSR Pixel size = 0.01745*R = approx 15m x 15m at R=850m

SSR-X System

Shading is the size of the radar beam

The red bock is the minimum size of failure that can be detected

SSR-X Pixel size = 0.008727*R = approx 7.5m X 7.5m at R=850m

SSR Specs Radar System with Pixel Processing

Post Processing Pixel size = real/3 = approx 5m x 5m at R=850m

MORE PIXELS NICER IMAGE BUT NO

DIFFERENCE TO THE SIZE OF FAILURE THAT

CAN BE RESOLVED BY THE RADAR SYSTEM !



Jan/2011

SSR Set UpSSR Set Up

Platform Requirements

Atmospheric Region Issues

Wall files without stable reference

region

Effect of Oblique Monitoring



Jan/2011

displacement

magnitude only

Atmospheric Region

Rotation of the SSRwill cause rotationof the atmospheric region



Jan/2011

Common Set Up ProblemsCommon Set Up Problems

Vegetation Traffic in the atmospheric

region

Atmospheric region not stable

SSR system not stable

Power cables in the scan area

Radar set up too far away, at ranges

exceeding 1750m and with huge scans



Jan/2011

Increasing Deformation



Jan/2011

Data Review ProcessData Review Process

Deformation Is it within normal limits purely stress relief or structurally

controlled deformation

Size of unusual deformation input into hazard/risk management techniques

Slope Instability Continual assessment of SSR data for selection of most

appropriate alarms

Input into hazard/risk management map/plans

Failure (functional failure or collapse) Back analysis of failure to determine geometry, alarm

settings, parameters etc



Jan/2011

Risk FrameworkRisk Framework

2. Identify

Hazard

Find areas

showing

excessive

deformation

3. Analyse

Hazard

Monitoring used

to assess

deformation

magnitude, rate,

failure size to

assess failure

4. Evaluate

Hazard

(use organisation

input to rank and

evaluate hazards)

Communicate and Consult (Train personnel on monitoring system use and show data)

6. Monitor and Review (Monitor movement and review alarms if set )

5. Treat Hazards

Reduce likelihood

by aiding

engineering control

of failure. Reduce

consequence by

set up of

geotechnical

monitoring alarm

system evacuation

1. Select Context

Select role for

monitoring

systems



Jan/2011

Session lessons to be learntSession lessons to be learnt

Importance of reviewing the SSR data to

ensure that the deformations measured

are not compromised by artificial effects

Some understanding of ambiguity,

atmospherics and minimum size

Value setting up scan to minimise

problems



Jan/2011

3 things to think about ?

1. Does any of this information change the

way you might use the radar?

2. Do you understand the importance of

good set up to reduce artificial effects?

3. Will georeferencing add value to your

operation?

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