EDM Height Traversing Levelling Survey Report

Transcription

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 Tuvalu, August 2010 Sam Griffiths, A. Lal Record 2012/24 GeoCat # APPLYING GEOSCIENCE TO AUSTRALIA S MOST IMPORTANT CHALLENGES

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3 EDM Height Traversing Levelling Survey Report TUVALU, August 2010 GEOSCIENCE AUSTRALIA RECORD 2012/24 Sam Griffiths 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: Griffiths, S., 2012, EDM Height Traversing Levelling Survey Report: Tuvalu, August Geoscience Australia, Record 2012/24. 31pp.

5 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 Contents Introduction...1 The Survey...1 Locations of Survey Bench Marks...2 The Tuvalu Datum...4 Equipment...4 Method...4 Survey Support...5 Issues...5 Description of Marks Tuvalu...6 Comparisons between 2009 and 2010 EDM Surveys...7 Combined Comparisons 1993 to Tuvalu 2010 Reduced Levels...9 Time Series of Bench Mark movement relative to the Fixed Deep driven Bench Mark - BM Deep Bench Mark Locality Diagrams...14 Permanent Holding Marks Locality Diagrams...20 TUVABM and TUVA Reference Mark Locality Diagrams...25 References...29 iii

6 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 iv

7 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 Introduction This report outlines the level survey completed during the visit to Tuvalu between August Personnel involved in the survey were Sam Griffiths, Geoscience Australia and Andrick Lal, Surveyor, Secretariat of the Pacific Islands Applied Geoscience Commission (SOPAC). This is the fourth EDM height traversing levelling survey of the deep bench mark array in Funafuti Atoll, Tuvalu. The previous levelling surveys using this technique were performed in 2005, 2007 and Precise Differential Levelling surveys were performed on eight occasions between 1993 and 2003 by the National Tidal Centre Australia (NTCA) and the survey in 2005 included a comparison between the precise differential levelling and EDM height traversing technique. This report contains a comparison between the 2009 and 2010 EDM height traversing results as well as a combined comparison since the first levelling survey in The Survey The EDM Height Traversing level survey was carried out between the six deep driven bench marks: BM22 BM23 BM24 BM26 BM27 BM28 Included in the survey was the CGPS Station bench mark, TUVABM, the SEAFRAME Sensor Bench Mark - TUV20, the Project Plaque point TUV19, at the Tide Gauge and Holding Marks TUV42, TUV100, TUV61, TUV48, TUV74, TUV73 and TUV101 All the other deep driven bench marks were located and found undisturbed and in good order. The EDM Height Traversing levelling technique was performed to the Class L2A, as per the Inter- Government Committee on Surveying and Mapping (ICSM), Standards and Practices for Control Surveys, SP1, Ver. 1.5, May After reduction an internal precision of 1mm K or better was achieved, where K is levelled distance in kilometres. Project Specification precision is 2mm K 1

8 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 Locations of Survey Bench Marks 2

9 EDM Height Traversing Levelling Survey Report: Tuvalu, August

10 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 The Tuvalu Datum The Datum for the survey is the University of Hawaii Tide Staff Zero (TSZ). Reduction of the data has been calculated holding BM22 fixed at metres TSZ, this value was determined by the NTCA in 1993 by : 1993 Adopting the height of UH 1 RL = metres TSZ 1994 Adopting the height of BM22 as derived from the 1993 survey RL = metres. Equipment Leica total station model TCA2300 Leica precision prisms GPH1P (2). Leica rigid tripod (GST40). Stainless steel target poles supported by Leica telescopic bi-poles (2). Leica cast iron change plates (2). Kestral 4000 pocket weather tracker Method Leap-Frog EDM-height-traversing: "Leap-Frog" EDM-height-traversing involves the one target remaining at a particular change point for both sightings. To avoid the possibility of the target being placed on a different point the target is not moved between the back-sight and foresight. Two target/reflectors are employed (on reflector rods with struts). As in spirit levelling, it is imperative that the electronic tacheometer (total station) is set up in the middle between the two reflectors. Recorded are the height differences (between the instrument s trunnion axis and the reflector) that are computed by the electronic tacheometers. In consequence, the ambient temperature and pressure must be input into the instrument since the slope distances must be corrected for temperature and pressure (first velocity correction) on-line (Rüeger & Brunner 1982). All observations were recorded digitally. 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. 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 project plaque BM and the SEAFRAME sensor BM. 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. Atmospheric readings were obtained using a Kestral 4000 pocket weather tracker. These atmospheric readings were recorded manually onto the Tuvalu levelling booking sheets and entered 4

11 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 into the total station prior to each level run and approximately every hour thereafter or when ever an obvious change in weather conditions was observed. Survey Support The Director of the Tuvalu Meteorological Service, Ms. Hilia Vavea and her staff provided valuable support during our visit. Special mention to Mr. Faatasi Malologa Director, Lands and Survey Department to arrange for the car hire and accommodation and also providing assistance on this visit for the clearance of the survey equipment from Customs. Mr Stanley Tala provided the labour assistance in the field. Issues No issues or concerns of any importance with regards to the levelling survey were encountered during the 2010 survey. Please note that due to fewer flights to Funafuti, it is advisable to hand carry the survey equipment as excess luggage from and to Funafuti as there will be delays in the air freight, if done so. 5

12 EDM Height Traversing Levelling Survey Report: Tuvalu, August 2010 Description of Marks Tuvalu BM22 is the bench mark held fixed with an RL = metres The height of BM22 was derived in 1993 by NTC by means of: 1993 Adopting the height of UH 1 RL = metres TSZ Adopting the height of BM22 from the 1993 survey. RL = Bench Marks: BM22, BM23, BM24, BM26, BM27 and BM28 are all Deep Driven BM s * BM25 has been destroyed. Point: TUV20 is the SEAFRAME Sensor Bench Mark TUV19 is the Project Plaque point TUVABM is the Reference Bench Mark for the CGPS Pillar. TUV42, TUV100, TUV101, TUV61, TUV48, TUV74, TUV73, TUV101, TUV102 are all permanent stainless steel bolt holding marks, drilled in concrete and glued in place. 6

13 Comparisons between 2009 and 2010 EDM Surveys Table 1: Tuvalu EDM Height Traversing Levelling Comparison and Table of Results. TUVALU EDM Height Traversing Levelling Comparison and Table of Results BM22 - Adopted fixed height (TSZ) FROM TO Levelled Height Difference Reduced Level 2010 Misclose (mm) Distance (Km) 1mm K Reduced Level 2009 Difference (mm) BM22 TUV TUV42 TUV TUV19 TUV BM22 TUV TUV100 BM BM23 TUV TUV101 TUV TUV61 TUV TUV48 TUV TUV74 BM TUV74 TUV TUV73 BM BM28 BM BM27 BM BM27 TUVABM TUV20 TUVABM Allowable Misclose is 2 K TUVABM TUVA An internal precision of 1mm K was achieved for all bays levelled - this is well within the Project Specification of 2mm K 7

14 Combined Comparisons 1993 to 2010 Table 2: Tuvalu - Comparison of the RL's for Precise Differential Levelling ( ) and EDM Height Traversing ( ). TUVALU RL Comparison Precise Differential Levelling and EDM Heigh t Traversing YEAR MARK BM22 BM23 BM24 BM25 BM26 BM27 BM28 TUV19 TUV20 TUVABM EDM EDM Destroyed EDM EDM

15 Tuvalu 2010 Reduced Levels DATE: AUGUST 2010 DATUM: TSZ (UNIVERSITY OF HAWAII TIDE STAFF ZERO) Table 3: Tuvalu Reduced levels and heights difference relative tobm22 from the 2010 survey POINT # 2010 Levelled diff. ht RL BM TUV42 TUV19 TUV BM TUV BM TUV TUV61 TUV48 TUV BM TUV74 TUV BM BM BM BM TUVABM

16 Time Series of Bench Mark movement relative to the Fixed Deep driven Bench Mark - BM 22 Precise Differential Levelling to 2003 (2005) EDM Height Traversing - commenced 2005 BM23 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey BM24 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 10

17 BM26 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey BM27 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 11

18 TUVABM 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey TUV19 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 12

19 TUV20 8 Relative Movement of Bench Mark (mm) Year of Levelling Survey 13

20 Deep Bench Mark Locality Diagrams 14

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26 Permanent Holding Marks Locality Diagrams 20

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31 TUVABM and TUVA Reference Mark Locality Diagrams 25

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35 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