EDM Height Traversing Levelling Survey Report

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1 G E O S C I E N C E A U S T R A L I A EDM Height Traversing Levelling Survey Report Rarotonga, Cook Islands, December 2009 N. J. Brown, A. Lal Record 2012/28 GeoCat # APPLYING GEOSCIENCE TO AUSTRALIA S MOST IMPORTANT CHALLENGES

3 EDM Height Traversing Levelling Survey Report Rarotonga, Cook Islands, December 2009 GEOSCIENCE AUSTRALIA RECORD 2012/28 N. J. Brown 1, A. Lal 2 1. National Geospatial Reference System, Minerals and Natural Hazards Division, Geoscience Australia GPO Box 378 Canberra ACT Secretariat of the Pacific Islands Applied Geoscience Commission (SOPAC)

4 Department of Resources, Energy and Tourism Minister for Resources and Energy: The Hon. Martin Ferguson, AM MP Secretary: Mr Drew Clarke Geoscience Australia Chief Executive Officer: Dr Chris Pigram Commonwealth of Australia (Geoscience Australia) 2012 With the exception of the Commonwealth Coat of Arms and where otherwise noted, all material in this publication is provided under a Creative Commons Attribution 3.0 Australia Licence ( Geoscience Australia has tried to make the information in this product as accurate as possible. However, it does not guarantee that the information is totally accurate or complete. Therefore, you should not solely rely on this information when making a commercial decision. ISSN ISBN GeoCat # Bibliographic reference: Brown, N. J. & Lal, A., 2012, EDM Height Traversing Levelling Survey Report: Rarotonga, Cook Islands, December Geoscience Australia, Record 2012/28. 24pp.

5 Contents Introduction... 1 The Survey... 1 Bench Mark Locality Diagrams... 2 The Cook Islands Datum... 3 Equipment... 3 Method... 3 Survey Support... 4 Issues...4 Description of Marks Rarotonga, Cook Islands... 4 Comparisons between 2009 and 2008 EDM Surveys... 5 Combined Comparisons 1993 to Cook Islands 2009 Reduced Levels... 7 Time Series of Bench Mark movement relative to Fixed Deep Bench Mark FSM Deep Bench Mark Locality Diagrams Cook Islands Reference Mark Locality Diagram Temporary Holding Mark Locality Diagrams References iii

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7 Introduction This report outlines the high precision level survey completed between the SEAFRAME tide gauge and continuous GPS station in Rarotonga, Cook Islands from 2 4 December Personnel involved in the survey were Nicholas Brown, Project Officer, Geoscience Australia and Andrick Lal, Surveyor, Secretariat of the Pacific Islands Applied Geoscience Commission (SOPAC). The EDM height traversing levelling technique was employed to observe differences in height between the deep bench mark array in Rarotonga, which runs approximately 2.2 km from the tide gauge sensor to the continuous GPS antenna. Previous levelling surveys have been conducted along the route using this technique in 2004, 2007 and In addition, precise differential levelling surveys were performed along the deep bench mark array from 1993 to 2004 by the National Tidal Centre (NTC) with the survey in 2004 including a comparison between the precise levelling and EDM height traversing technique. This report contains a comparison between the 2009 and 2008 EDM height traversing results as well as a combined comparison since the first levelling survey. The Survey The EDM height traversing levelling survey was carried out between the SEAFRAME tide gauge sensor, continuous GPS station and the deep driven bench mark array: BM26 deep driven benchmark COO56 SEAFRAME sensor benchmark COO10 Project plaque point BM18 local survey department benchmark BM33 deep driven bench mark BM27 reference bench mark for the survey (RL = metres) BM34 deep driven bench mark BM28 deep driven bench mark BM35 deep driven bench mark CKISBM reference bench mark for the CGPS pillar Also included in the survey were temporary holding marks COO77, COO84, COO85, COO92, COO100, COO101 as well as the CGPS reference point - CKIS and the three CGPS Reference Marks - RM1, RM2 and RM3. All the deep bench marks were located and found in good order and undisturbed. The EDM height traversing levelling technique was performed to the Class L2A specifications (ICSM, Standards and Practices for Control Surveys). After reduction an internal precision of 1mm K or better was achieved, where K is distance in kilometres. This is well within the project specification of 2mm K. A table of results and comparisons and the 2009 reduced levels are detailed later in this report. 1

8 Bench Mark Locality Diagrams 2

9 The Cook Islands Datum The Datum for the survey is Mean Sea Level (MSL). All reduced levels for the Rarotonga levelling survey are relative to BM27 fixed at m. This value was determined by the NTC in Equipment Leica total station model TCA1800L Leica precision prisms GPH1P (2). Leica rigid tripod. Stainless steel target poles supported by Leica telescopic bi-poles (2). Shortened stainless steel target pole for the SEAFRAME sensor BM connection. Leica cast iron change plates (2). Kestral 4000 pocket weather tracker Method The Leap-Frog EDM-height-traversing technique was employed for the Rarotonga tide gauge levelling survey. The "Leap-Frog" EDM-height-traversing technique involves setting up a total station (TCA1800L) midway between two target/reflectors (on reflector rods with struts). The targets remain at a particular change point for the back-sight and fore-sight observations. The instrument measures slope distances (±1mm) and vertical angle (1 ) to derive height differences (between the instrument s trunnion axis and the reflectors). In support of the slope distance observations, the ambient temperature, pressure and humidity are recorded (Kestral 4000 pocket weather tracker) and input into the instrument to apply the first velocity correction to the observed distances (Rüeger & Brunner 1982). Several rounds (four) of observations are taken to the backsight and fore-sight targets from each instrument setup. All levelling bays started and finished with the same reflector and reflector rod, ie an even number of setups when the two reflector rod configuration was used this eliminates any reflector rod zero error. Results can also be gained with the EDM Height Traversing method by using a single set-up / single rod configuration. This single set-up / single rod configuration is particularly useful when levelling between bench marks which are close together e.g. between the CGPS RMs. Reduction of the digital data was computed by the Geoscience Australia levelling program leveling1.exe. This program computes the height difference between the two reflectors at any one set-up. 3

10 Survey Support The survey team very much appreciated the assistance from Lands and Survey Department (Ministry of Works) and the Meteorological Department. Personnel consulted during the visit were: Mr. Keu Mataora Director, Ministry of Works Mr. Timoti Tangiruaine Project Officer, Ministry of Works Mr. Vaipo Matoara GIS, Ministry of Works Mr Arona Ngari, Director of the Cook Islands Meteorological Office was away during this visit. Both departments have a keen interest in the SPSLCMP and are always supportive with any associated project matters. Issues Customs clearance of the survey equipment is to be arranged prior to the visit to Cook Islands. It is advisable to arrange access and security passes to the airport area prior to arrival in Cook Islands. This can be done through personnel from Ministry of Works. Description of Marks Rarotonga, Cook Islands BM26 deep driven benchmark COO56 SEAFRAME sensor benchmark COO10 Project plaque point BM18 local survey department benchmark BM33 deep driven bench mark BM27 reference bench mark for the survey (RL = metres) BM34 deep driven bench mark BM28 deep driven bench mark BM35 deep driven bench mark CKISBM reference bench mark for the CGPS pillar CKIS CGPS reference point CKIS RM1 3 CGPS reference marks Temporary holding marks COO77, COO84, COO85, COO92, COO100, COO101 are are permanent stainless steel bolt holding marks, drilled in concrete and glued in place. 4

11 Comparisons between 2009 and 2008 EDM Surveys Table 1: Rarotonga, Cook Islands 2009 EDM Height Traversing Levelling Comparison BM27 - ADOPTED FIXED HEIGHT M BACK SIGHT FORE SIGHT LEVELLED HEIGHT DIFF REDUCED LEVEL 2009 MISCLOSE (MM) DISTANCE (KM) 1MM K REDUCED LEVEL 2008 DIFF (MM) BM BM33 BM BM18 BM COO10 COO COO10 COO BM BM COO77 COO COO92 COO COO100 COO BM34 BM COO84 COO BM28 BM BM35 BM COO85 COO COO101 COO CKISBM Misclose for all bays levelled = Allowable misclose 2 K An internal precision of 1mmK was achieved for all bays levelled - this is well within the project specification of 2mm K CKISBM CKIS CKISBM RM CKISBM RM CKISBM RM

12 Combined Comparisons 1993 to 2009 Examination of the level survey results indicate no significant displacement of any of the deep driven bench marks, tide gauge sensor of CGPS benchmarks. Table 2: Rarotonga, Cook Islands - Comparison of the RL's for Precise Differential Levelling ( ) and EDM Height Traversing ( ). YEAR BM 18 BM 26 BM 27 BM 28 BM 29 BM 33 BM 34 BM 35 COO 10 COO 56 CKISBM EDM

13 Cook Islands 2009 Reduced Levels DATE: 2 4 DECEMBER 2009 DATUM: MEAN SEA LEVEL Table 3: Rarotonga, Cook Islands Reduced levels and heights difference relative to BM27 from 2009 survey POINT # 2009 LEVELLED DIFF. HT RL BM (fixed) BM BM COO COO BM COO COO COO BM COO BM BM COO COO CKISBM

14 Time Series of Bench Mark movement relative to Fixed Deep Bench Mark FSM1 Precise Differential Levelling: EDM Height Traversing: 2004 onwards BM 26 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 8

15 BM 28 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey BM 34 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 9

16 BM 33 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey BM 29 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 10

17 BM 35 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey COO 10 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 11

18 COO 56 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey CKISBM 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 12

19 Deep Bench Mark Locality Diagrams 13

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25 Cook Islands Reference Mark Locality Diagram 19

26 Temporary Holding Mark Locality Diagrams 20

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29 References Rüeger, J.M. & Brunner, F.K. 1982, EDM Height Traversing versus Geodetic Levelling, The Canadian Surveyor, vol. 36, no. 1, pp Inter-Government Committee on Surveying and Mapping (ICSM) 2002, Standards and Practices for Control Surveys, SP1, Ver. 1.5, May

Survey Report. EDM Height Traversing Levelling Survey. Cook Islands. June 2008

Survey Report. EDM Height Traversing Levelling Survey. Cook Islands. June 2008 South Pacific Sea Level and Climate Monitoring Project (SPSLCMP) Survey Report EDM Height Traversing Levelling Survey Cook Islands June 2008 This project is sponsored by the Australian Agency for International