Publication 15_H055. Absolute and Relative Gravity Survey University of Hawai i-manoa and Pier 35 Honolulu, Hawai i. February - March 2015

Transcription

1 GEODETIC SURVEYS DIVISION UNCLASSIFIED 314 Publication 15_H055 Absolute and Relative Gravity Survey University of Hawai i-manoa and Pier 35 Honolulu, Hawai i February - March 2015 UNCLASSIFIED 2. NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY

2 Absolute and Relative Gravity Survey University of Hawai i-manoa (UH) & UH Marine Center-Pier 35 Honolulu, Hawai i February-March 2015 TABLE OF CONTENTS 1. Introduction...2 a. Background...2 b. Points of Contact Requirements Procedure...2 a. Absolute Gravity...2 b. Relative Gravity Computations and Analysis...3 a. Absolute Gravity...3 b. Relative Gravity Survey Results Station Descriptions...5 1

3 1. Introduction a. Background This report presents the results of a gravity survey at the University of Hawai i-manoa (UH), Institute of Geophysics and UH Marine Center, Honolulu, Hawai i. The survey was conducted by Mr. R. David Wheeler (Team Lead: ), John Maurais and SFC Brad Favinger of the National Geospatial-Intelligence Agency (NGA). Survey dates were 27 February thru 9 March b. Point of Contact: Scott Ferguson Director of Marine Technical Services UH Marine Center # 1 Sand Island Access Road Honolulu, Hawaii, Tel: (808) jscottf@hawaii.edu 2. Requirements Gravity values were requested at two locations, the University of Hawai i-manoa, Institute of Geophysics, Laboratory s Isolation Table and UH Marine Center s new location, currently under construction at Pier 35. And if time permitted a third location was requested at the UH Marine Center s current location at Pier 45, Sand Island. The acceleration of gravity accuracy requirements for this survey were: +/ milligal (mgal)(1-sigma) absolute and +/ mgal (1-sigma) relative to the absolute station. 3. Procedures a. Absolute Gravity: Two absolute stations were established, one at UH Institute of Geophysics (UH HIG AA) and one at the 84 th Engineering Battalion, Schofield Barracks (84 th AA) with a Micro G LaCoste A-10 (serial number 009) gravity meter. Multiple day independent measurements were made at both absolute stations. 2

4 b. Relative Gravity: Relative observations from the established absolute station (UH Institute of Geophysics) were made using a type loop structure with three Scintrex CG-5 Autograv gravity meters (Serial Numbers 40244, and 40248). The loop structure included relative measurements at UH HIG Excenter, Pier 35 Alpha, Pier 35 Bravo, Pier , Pier 425, Pearl Harbor BA (Origin of a 1999 gravity survey) and 84 th AA (used to validate the absolute gravity data). 4. Computations and Analysis a. Gravity Absolute: The absolute gravity value for both stations were determined from data collected with a Micro G LaCoste A-10 gravity meter. More than 4 days of independent observations were taken at both stations. A weighted mean of these observations was calculated at both stations and these values were compared via relative ties to each other. Absolute station comparisons (absolute versus relative) were less than mgal (1- sigma). The absolute precision terms were less than mgal for both stations. Using the Scintrex CG-5 relative meters a gradient value (microgal/centimeter) at each absolute site was determined. This gradient was applied to the absolute gravity value to relocate it from the A-10 s measurement location (approximately 71 centimeters above) to the established gravity monument on the ground. b. Gravity Relative: A dynamic drift value is computed from the observations at the control station for each meter. This is applied to the individual observations, linearly; by time. The relative gravity value for each station was determined from data collected with the CG-5 meters. The output from these meters is automatically corrected for static drift and earth-tide effects. The delta gravity value of the observations from each meter is then processed with NGA proprietary GravNet software. These delta s were then applied to the absolute station to determine the gravity value at each measured relative gravity station. The relative precision terms were less than mgal for all stations. 3

5 5. Gravity Results Absolute Gravity Values STATION NAME City ADJUSTED GRAVITY mgal PRECISION TERM mgal UH HIG AA Manoa th AA Schofield Barracks Relative Gravity Values STATION NAME City ADJUSTED GRAVITY mgal PRECISION TERM mgal UH HIG Excenter Pier 35 Alpha Pier 35 Bravo Pier Pier Pearl Harbor BA 84 th AA (Comparison Value) Manoa Honolulu Honolulu Sand Island Sand Island Pearl Harbor Schofield Barracks

6 GRAVITY STATION UH HIG AA LOCATION DESCRIPTION OF GRAVITY STATION Approx. WGS 84 Position Lat: 21 17'52.1"N Long: '00.0"W University of Hawai i-manoa, Institute of Geophysics DESCRIBED BY Wheeler ESTABLISHED BY DATE NGA/SNSH March 2015 The station is located in the basement of University of Hawai i- Manoa, Institute of Geophysics, Honolulu, Hawai i. The station is the center of the top of the 3 x 5 concrete isolation table. Entrance is through the south side of the building down a ground level flight of stairs. First door on your left (Room B5). N 5

7 DESCRIPTION OF GRAVITY STATION GRAVITY STATION NAME Approx. WGS 84 Position Honolulu G (UH HIG AA Excenter) LOCATION Lat: 21 17'52.6"N Long: '00.3"W University of Hawai i-manoa, Institute of Geophysics DESCRIBED BY Wheeler ESTABLISHED BY DATE NGA/SNSH March 2015 The station is located outside on the 1 st floor near Room 108 on the southwest side of University of Hawai i-manoa, Institute of Geophysics Bldg. The station is the USAMSFE International Gravity Base Station bronze disk stamped Honolulu G and is locally referred to the as the Wollard Mark. It is set in a sidewalk approximately 0.1 meters from the building wall. Honolulu G N 6

8 GRAVITY STATION Pier 35 Alpha LOCATION DESCRIPTION OF GRAVITY STATION WGS 84 POSTION Lat:21 18'55.937"N Long:157 52'37.556"W EH:18.31m University of Hawai i, New Marine Center, Pier 35, Honolulu, Hawai i DESCRIBED BY Wheeler ESTABLISHED BY DATE NGA/SNSH March 2015 The station is located at the University of Hawai i, Marine Center, Pier 35 at the 550 foot mark along the north-south Pier. The station is a 3 Brass NGA Gravity Station disk stamped Pier 35 Alpha Pier 35 Alpha N 7

9 GRAVITY STATION Pier 35 Bravo LOCATION DESCRIPTION OF GRAVITY STATION Approx. WGS 84 Position Lat: 21 18'56.2"N Long: '34.5"W University of Hawai i-manoa, New Marine Center, Pier 35, Honolulu, Hawai i DESCRIBED BY Wheeler ESTABLISHED BY DATE NGA/SNSH March 2015 The station is located at the University of Hawai i, new Marine Center, Pier 35 on the first floor under a stairwell of the still under construction Marine Center building. The station is a 3 Brass Gravity Station disk stamped Pier 35 Bravo Pier 35 Bravo N 8

10 DESCRIPTION OF GRAVITY STATION GRAVITY STATION Approx. WGS 84 Position 84 th AA Lat: 21 29'49.5"N Long: "W LOCATION DESCRIBED BY 84 th Engineering Battalion Building, Schofield Wheeler Barracks, Hawai i ESTABLISHED BY DATE NGA/SNSH March 2015 The station is located on the first floor of 84 th Engineering Battalion Building on Schofield Barracks, Hawai i in the southwest corner of the surveyors equipment storage room. The station is a 1 Brass Gravity Station disk stamped 84 th AA 84 th AA N 9