GNSS VerificationGNSS Verification

Derrin LeeDerrin LeeRegistered Mining SurveyorRegistered Mining Surveyor

Xstrata Glendell MineXstrata Glendell Mine

AIMS Mudgee SeminarAIMS Mudgee Seminar

February 2008February 2008

The purpose of this presentation is to The purpose of this presentation is to raise awareness of this issue and to foster raise awareness of this issue and to foster debate. debate.

This topic is considered by many as a This topic is considered by many as a “Grey Area”. “Grey Area”.

Each surveyor should arrive at their Each surveyor should arrive at their own conclusions as to what is necessary in own conclusions as to what is necessary in order for them to comply with applicable order for them to comply with applicable regulations.regulations.

Disclaimer:Disclaimer:

What are GNSS?What are GNSS?

GGLOBALLOBALNNAVIGATIONALAVIGATIONALSSATELLITEATELLITESSYSTEMSYSTEMS(Cl 5 Surveying Regulation 2006)(Cl 5 Surveying Regulation 2006)

What are GNSS?What are GNSS?Most surveyors are familiar with the Most surveyors are familiar with the Global Global Positioning System (GPS)Positioning System (GPS). .

GNSS GNSS is relatively new terminology.is relatively new terminology.

It describes not only It describes not only GPSGPS, but the whole , but the whole range of emerging satellite positioning range of emerging satellite positioning technologies.technologies.

These technologies include:These technologies include:

The European Commission's The European Commission's GALILEOGALILEO,,

Russia's Russia's GLONASS GLONASS & China’s& China’s COMPASS COMPASS..

GPS turned 30 yesterday, 22nd February 2008.

The first GPS Satellite (SVN01) was launched from Vandenberg Air Force Base California on 22nd February 1978.

Who currently uses GNSS?Who currently uses GNSS?How many people here today use GNSS?How many people here today use GNSS?

Which methods do you use:Which methods do you use:

•Real Time Kinematic (RTK)Real Time Kinematic (RTK)

•Post Processed Single Baselines (Static or Fast Post Processed Single Baselines (Static or Fast Static)Static)

•Post Processed Multi Baseline (e.g. AUSPOS Online Post Processed Multi Baseline (e.g. AUSPOS Online Processing)Processing)

•Network base solutions (e.g. VRS or CORS such as Network base solutions (e.g. VRS or CORS such as SydNET)SydNET)

Limitations of GNSS

GNSS observations are currently NOT traceable to a recognised value standard.

All GNSS are operated by INTERNATIONAL parties.

These ARE NOT under the surveyor’s direct control.

As such, any GNSS equipment and techniques used must be validated.

Verification or Calibration?

Unlike EDM equipment, GNSS receivers cannot be calibrated for scale.

Verification IS NOT Calibration

Calibrate:– Adjust, attune, standardise.

Verify:– Confirm, authenticate, corroborate, make sure.

Why verify your GNSS?

Why do you verify your EDM?

As a professional surveyor it is in your interest not to use any measuring equipment unless you know the accuracy obtained by its use.

The “Survey And Drafting Directions For Mine Surveyors 2007 (NSW – COAL)” require surveys to be carried out to a standard.

To provide Legal Traceability

What the Mining Regulations say:

S+DD For Mine Surveyors 2007(NSW – COAL)

3.3.1 Accuracy: Each control survey and subsidiary survey must be planned and surveyed to ensure these surveys satisfy the conditions to achieve a standard of accuracy as prescribed in ICSM, SP1 to achieve Class D or better.

3.3.3 Secondary surveys shall be employed by the Mining Surveyor where necessary to accurately locate all of the Mine workings on the Mine Workings Plan to within 1mm at 1:2000 Scale. (i.e. 2m) Such surveys shall be completed to the highest appropriate standards of accuracy.

S+DD For Mine Surveyors 2007(NSW – COAL)

3.5.1 Order of accuracy of benchmarks:Such levelling shall be completed to ICSM SP1 Class “LD” or Class “B” standards of accuracy.

3.5.2 Accuracy of Mine workings:Such levelling shall be completed to ICSM SP1 Class LE standard of accuracy or to within 0.1 metre.

STANDARDS AND PRACTISES FOR CONTROL SURVEYS

ICSM SP1 (Version 1.6)

Part B 2.6 Global Positioning System

2.6.4If required, the equipment and software can be validated over existing, high quality geodetic network marks.

SURVEY AND DRAFTING DIRECTIONS FOR MINING SURVEYORSIssued as an adjunct to General Rule 2000 under the Mines Inspection Act 1901

3.11 Maintenance and Adjustment of Survey Equipment

3.11.1 Survey equipment used for baseline or other precise surveys should be maintained regularly and kept in good adjustment.

3.11.3 GPS equipment should be verified against an approved control network upon acquisition and after any change in software, firmware or hardware.

What the Land Surveying Regulations say:

Surveying Regulation 2006 (NSW)

Cl 3 Application of Regulation

This Regulation applies to all land surveys, and to all surveys referred to in section 4 or 5 of the Act, but does not apply to any mining surveys except to the extent to which the other provisions of this Regulation expressly provide and to the extent provided by an order in force under clause 4.

Surveying Regulation 2006 (NSW)

Cl 4 Mining surveys

(1) The Surveyor-General may, by order published in the Gazette, give directions with respect to the conduct of mining surveys.

(2) Such an order may only be made on the recommendation of the Board.

(3) The document entitled Survey and Drafting Directions for Mine Surveyors, published in March 2000 by the Department of Mineral Resources, is taken to be an order under this clause with respect to mining surveys carried out for the purposes of the Coal Mines Regulation Act 1982 and the Coal Mine Health and Safety Act 2002, and may be amended and repealed accordingly.

(4) The document entitled Survey and Drafting Directions for Mining Surveyors, published in December 2001 by the Department of Mineral Resources, is taken to be an order under this clause with respect to mining surveys carried out for the purposes of the Mines Inspection Act 1901 and the Mine Health and Safety Act 2004, and may be amended and repealed accordingly.

Surveying Regulation 2006 (NSW)

Cl 14 Equipment for measurement of surveys

(5) A surveyor must not use any GNSS equipment in making a survey unless it is verified against the State control survey: (a) at least once every year, and(b) immediately after any service or repair, and(c) immediately after any change or upgrade of

software.(6) The accuracy and method of any verification

under this clause must be as approved.

Surveyor General’s DirectionsNo. 9 - GPS Surveys

Currently under review

A draft document has been prepared as:

Surveyor General’s Directions No. 9GNSS for Cadastral Surveys

In light of the non prescriptive mining regulations:

I believe that the Draft Surveyor General’s Direction No. 9 provides the best indication of the current thinking on using GNSS for legal purposes.

Draft Direction No.9

This draft has been prepared by:

Simon McElroySenior Surveyor (Geodesy and CORS)Survey Infrastructure and GeodesyLand and Property InformationNSW Department of Lands

These are Simon’s thoughts.

They are not official.

Draft Direction No.9

Draft Direction No.9

Legal traceability of GNSS measurements is an extremely complex issue.

At the present time it is unresolved at a State, Federal & International level.

In the interim surveyors are strongly encouraged to connect to marks in the NSW State Survey Control network that have legal traceability.

Draft Direction No.9

Responsibility of the surveyor to ensure that their GNSS equipment and techniques will achieve a result in terms of the accuracy required. The most appropriate way to maintain accuracy is by connection to the State Survey Control Network. This will validate the surveys reliability, scale and orientation.

Draft Direction No.9

Surveyors are strongly encouraged to connect to marks in the NSW State Survey Control network that have legal traceability; these include:

Established marks Accurate AHD marks

(as per the Surveying Regulation 2006)

Draft Direction No.9

Surveyors should not be deterred from using GNSS for legal purposes provided that they:

Adopt GNSS best practice guidelines. Confirm at least one GNSS observation against established marks for each survey. Validate their GNSS techniques annually against higher order marks in the State Survey Control Network.

Draft Direction No.9

Survey Confirmation (Each Survey)

A basic two dimensional “relative” check only. At least one independent GNSS observation confirmed against an external source. Confirmation is achieved if the measurement satisfies the accuracies required by the Surveying Regulation 2006. The above obviously applies to cadastral surveying. A suitable substitution for mine surveying might be: Measurement satisfies the accuracies required by the Survey and Drafting Directions.

Draft Direction No.9

Annual Validation

A rigorous 3D “absolute” validation. Conducted annually for each GNSS equipment or technique used. Techniques must be the same as typically used by the surveyor. Minimum of 4 Marks. Hz Order 2 or better. Vrt Order L3 or better. Latest coordinates obtained from SCIMS. Values of one station held fixed. Coordinates of other stations determined by GNSS technique.

Draft Direction No.9

Annual Validation

Fixed station

Non fixed station

Non fixed stationNon fixed station

Draft Direction No.9

Annual Validation

Difference between derived coordinates and SCIMS used to determine if validation is acceptable.

Validation acceptable if difference is:

<25mm + 5ppm Hz and < 60mm+ 12ppm Vrt.

ppm is calculated on the distance between the non fixed stations.

Draft Direction No.9

Annual Validation

The validation should be repeated if changes/upgrades are made to:

GNSS Receivers (Hardware or Firmware) Techniques used Processing Software

Draft Direction No.9

State GNSS Test Networks

The Surveyor General has established two precise GNSS networks. Bass Hill and Newcastle University. These may be used for annual validations. Precise 3D coordinates are available for all marks. (They may differ slightly from SCIMS). Detailed instructions are available from the Department of Lands.

A Hypothetical Scenario Open cut coal mine. Survey Method: RTK GNSS (GPS + GLONASS)

GNSS Base fixed at survey office. A “Site Calibration” is used for day to day

RTK surveying.

What could the surveyor do to verify their equipment?

Firstly: Is a “Site Calibration” a verification of my equipment? NO Using a “Site Calibration” results in a correction

being applied to each RTK measurement. The correction is calculated as a best fit to the

control stations used in defining the “Site Calibration”.

(If the “Site Calibration” is used as part of everyday surveying it should be used when verifying the survey technique.)

Annual Validation

Identify at least 4 Marks in SCIMS with at least Order 2 Hz and Order L3 in the vicinity.

Select marks that surround the workings. Where possible include the Mine Baseline terminals.

Survey the marks using the same techniques typically used. Don’t forget you are validating your software and hardware. Consider the geoid model.

With the GNSS Base fixed determine the coordinates of the 4 marks.

Annual Validation

Determine the difference between the surveyed coordinates and SCIMS coordinates.

The validation could be seen as acceptable if the difference is:

<25mm + 5ppm Hz

and < 60mm+ 12ppm Vrt.

Survey Confirmation Each survey:- At least one independent GNSS

observation confirmed against an external source is required.

Make a measurement to a mark of the required order in SCIMS.

If there is no convenient mark in SCIMS consider placing and surveying your own mark to the required order.

Refer to the S+DD for the required accuracy of the confirmation. It will depend on the requirements of the survey.

Best Practise Guidelines

I would recommend that all surveyors using RTK techniques read:

SP1 Part B 2.6.8.4

Observational Requirements for RTK GPS Techniques

ReferencesReferences S+DD For Mine Surveyors 2007(NSW – COAL)S+DD For Mine Surveyors 2007(NSW – COAL) STANDARDS AND PRACTISES FOR CONTROL SURVEYSSTANDARDS AND PRACTISES FOR CONTROL SURVEYS

ICSM SP1 (Version 1.6)ICSM SP1 (Version 1.6) SURVEY AND DRAFTING DIRECTIONS FOR MINING SURVEYORSSURVEY AND DRAFTING DIRECTIONS FOR MINING SURVEYORS

Issued as an adjunct to General Rule 2000 under the Mines Issued as an adjunct to General Rule 2000 under the Mines Inspection Act 1901Inspection Act 1901

Surveying Regulation 2006 (NSW)Surveying Regulation 2006 (NSW) Surveyor General’s DirectionsSurveyor General’s Directions

No. 9 - GPS SurveysNo. 9 - GPS Surveys

LinksLinks

http://www.lands.nsw.gov.au/about_us/publications/guidelines/surveyhttp://www.lands.nsw.gov.au/about_us/publications/guidelines/surveyor_generals_directionsor_generals_directions

http://www.insidegnss.com/abouthttp://www.insidegnss.com/about

QuestionsQuestions

The EndThe End

Use of RTK GNSS Techniques to survey Mine Workings

A RTK survey, as carried out in most open cut coal mines to locate mine workings, is in effect a series of radiations from a single fixed GNSS base station.

This can be equated with an underground mine surveyor who utilises a total station to measures distances and directions from a control station to determine the location of underground mine workings.

The RTK radiations used to survey workings are not “Control or Subsidiary Surveys”. The best way to classify them is as “Secondary Surveys”.

S+DD 2. DefinitionsSecondary Surveys: A survey based on Control Surveys or Subsidiary Surveys utilised by the Mining Surveyor to accurately locate all of the workings of the Mine that are not included in Control Surveys or Subsidiary Surveys.

S+DD 3.3.3 Secondary Surveys shall be employed by the Mining Surveyor where necessary to accurately locate all of the Mine workings on the Mine Workings Plan to within 1mm at 1:2000 Scale. Such surveys shall be completed to the highest appropriate standards of accuracy.

So 3.3.3 informs us that Secondary Surveys are allowed, and that the required accuracy of the surveyed mine workings is 2m (i.e. 1mm at 1:2000).

What about heights?

S+DD 3.5.2

Accuracy of Mine workings: Such levelling shall be completed to ICSM SP1 Class LE standard of accuracy or to within 0.1m.

So provided that the GNSS base station location is derived from a Control Survey or Subsidiary Survey (i.e. Surveyed to Class D Horizontal and Class LD or B Vertically) and Mine Workings are located to with 2m horizontally and 0.1m vertically then the surveyor is in compliance with the S+DD.

There is no explicit requirement of the S+DD to verify the accuracy of the GNSS equipment when used for a Secondary Survey. It might be considered good practice to survey a check radiation to a known point before and after surveying Mine Workings. This is analagous with an underground surveyor who, when set over a control mark with a total station, takes a backsight and then confirms their orientation by checking to another control station.

For Control and Subsidiary surveys the S+DD requirement to verify the accuracy of GNSS equipment is implied through the requirement to comply with SP1.

If RTK techniques are used to perform “Control Surveys” then they must comply with the requirements of SP1 in order to achieve results of Class D. (S+DD 3.3.1)

To comply with SP1, new stations are recommended to be re-occupied from a minimum of two base stations.

It is desirable for some new stations to be re-occupied from a third base station.

It is also necessary to conduct an analysis to determine the class of survey actually achieved.