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SCAR Report 23

The Establishment of GPS Control Network and Data Analysis in the Grove Mountains, East Antarctica

E Dongchen(1), Zhang Shengkai(1), Yan Li(2) and Li Fei(2)
(1) Chinese Antarctic Center of Surveying and Mapping, Wuhan University, Wuhan, 430079, China
(2) School of Geodesy and Geomatics£¨Wuhan University, Wuhan£¨430079£¨China

Email: edc1939@public.wh.hb.cn

Abstract

In order to provide the satellite image map for the field expedition, during the 19th CHINARE (Chinese National Antarctic Research Expedition) 2002/2003 summer season, GPS control network was established in Grove Mountains, East Antarctica. Its geographical extension is 72º to 73ºS, 73º to 76ºE, and its area is about 8000km2. In the inland ice sheet where the elevation is approximately 2000m, seven permanent GPS control marks were set with the support of helicopter and vehicles. Simultaneously observing with Zhongshan permanent GPS station, we constructed the geodetic network with these seven points by Trimble 4000ssi GPS receiver. Processed by the high-accuracy GPS software°™GAMIT, the positioning precision is good enough to satisfy with the acquirement of cartography in this area.

Key Words geodetic network, satellite image, Grove Mountains, Antarctica

1. Background

Grove Mountains is located in Princess Elizabeth land in East Antarctica, about 400km inland from Zhongshan Station and 160km east of the Mawson Escarpment, it consists of a scattered group of mountains and nunataks. The range includes 73°_76°E, 72º_73°S, extending an area of 8000km2. Grove Mountains has great topographical undulation and is densely covered by ice crevice, the weather there is atrocious [1]. The average temperature in January is -18.5_ which is 18_ lower than Zhongshan Station, and the average wind velocity is more than 10m/s [2]. So it has been one of our ideal midway station points in the route from Zhongshan Station to eastern Antarctic ice-cover and in the expedition of Antarctic Pole Point.
During the 1998/1999 Antarctic summer season, the 15th CHINARE (Chinese National Antarctic Research Expedition) first went to the Grove Mountains for research and expedition. During the 1999/2000 summer season, the 16th CHINARE carried out the second expedition in the Grove Mountains, the surveyors utilized the Differential GPS technology and mapped the core area which covers 110 km2 at the scale of 1:25000 [3]. In the summer 2002/2003, it is the third time that the 19th CHINARE went to the Grove Mountains, the surveyors established 7 permanent geodetic points in this area, collected data on those points with GPS receivers, and prepared for the topographic mapping with the satellite image.
Besides CHINARE, ANARE (Australia National Antarctic Research Expedition) and RAE(Russian Antarctic Expedition) also have been to the Grove Mountains several times since 1950s[4].

2. Geodetic surveys 2002/2003 in the Grove Mountains

During the 2002/2003 summer season, the 19th CHINARE carried out the third expedition in the Grove Mountains, the main tasks include: geodetic survey, meteorite collection, ice kinematics and geology expedition etc.
In order to provide the satellite image map for the field expedition, the surveyors established 7 permanent geodetic points in Cooke PK°¢the north section of the Gale Escarpment°¢Mount Harding°¢Melvold NTKS°¢Black NTKS°¢the south section of the Gale Escarpment and the middle section of the Gale Escarpment, and the GPS control network is shown in Fig.1.

Fig.1: GPS control network in the Grove Mountains
(Note: the coordinates in Fig.1 are the approximate coordinates with single point positioning)

In January 19, 2003, the Z-9 helicopter flew from Zhongshan Station to the camp No.5 at the foot of the Mount Harding, then the helicopter flew to the Cooke PK for GPS observation and ice sampling etc. This is the first time that Chinese helicopter flew to the Grove Mountains under the furious weather conditions without foreign aids. On account of the long distance between Zhongshan Station and the Grove Mountains, the fuel carried by the helicopter can only maintain the single fly to the Grove Mountains, the helicopter had to be replenished the fuel so that it can fly back to Zhongshan Station. But the temperature in the Grove Mountains is so low that the helicopter couldn’t close the engine, so the helicopter can only stay in the Grove Mountains for a short time.
Shortly after its arrival at camp No.5, the helicopter carried the surveyors to Cooke PK. Because the wind near the foot of the Cooke PK is too violent, the helicopter had to land on ice far away. The permanent geodetic mark which carved Z001 was established on a nunatak to the south of Cooke PK, the mark is illustrated in Fig.2 below. Only small amount of data were collected on this point because the helicopter had to fly back in an hour.

Fig.2: GPS benchmark in the Grove Mountains

Except for Cooke PK, snow vehicles were utilized when collecting GPS data on other 6 points. On the apparent and flat solid bedrock, the surveyors used the impact drill to drill an aperture in the bedrock, then put the screw of the benchmark into the aperture and clung it with glue. After the benchmark was stable enough, the GPS antenna was mounted over the benchmark and began to collect data. About one hour’s GPS data were collected on each point. The satellite cutoff angle was set to 15 degree and the sample interval was 15 second. After observation, photos were taken from different directions for the benchmark. GPS observation in the Grove Mountains is shown in Fig.3.

Fig.3: GPS observation in the Grove Mountains

The observation records are shown in table 1.

3. Data Processing

A high-accuracy GPS processing software package£∫GAMIT was utilized, and the data were processed on ULTRA2 workstation. GAMIT is a comprehensive GPS analysis package developed by MIT and Scripps for the estimation of three-dimensional relative positions of ground stations and satellites orbits. The software is composed of ARC°¢Model°¢SINCLN°¢DBCLN°¢CVIEW and SOLVE modules etc[4].
The data were processed using IGS precise ephemeris in the ITRF 2000 Reference Frame, at epoch 2000 and the baseline was constituted with the Zhongshan permanent GPS station. The ephemeris precision is one of the most important factors in GPS data processing, and its influence on baseline processing can be given in the formula below:

The main limiting factors in GPS baseline processing are listed below:

The quality of the data is also important for the precision and reliability of baseline. The data edit which included fixing the cycle slips and eliminating the remained residuals is the main job in processing data. When editing the data, run AUTCLN module firstly, which allows better handling of poor data and provides quality statistics for each station. Then CVIEW should be run to examine the phase residuals from the initial solution and to add instructions for deleting data to the AUTCLN command file and fix remaining small cycle slips interactively. After that, clean X-file can be drawn for baseline resolution [6].
Basing on the data edit, ARC°¢MODEL and SOLVE can be run sequentially. The coordinates of the control points are shown in table 2.

The precision of the control points are listed in table.3:


From table 3, the conclusion can be drawn that the precision of Z001 is poor because of the short observation time. Besides Z001 point, the other 6 points can satisfy the need of the satellite image mapping at the scale of 1:50000.

4. Conclusion and suggestions

The precision of the 6 points in the Grove Mountains except for Z001 are high enough to satisfy the need of the satellite image mapping at the scale of 1:50000.
Because of the limitation of the logistic support, short term GPS data were observed at Z001 point. As a result, the precision of this point is too low to use. If it is possible, Z001 should be re-observed in next expedition and 2_3 points should be established in the north part of the Grove Mountains, so the geodetic network would be more equivalent.
2_3 points should be re-observed in next expedition so as to get multi-session repetitive data for analysis of the crustal movement and geodynamics. The control points in the Grove Mountains can be analyzed together with the points in Larsemann Hills and Amery Ice Shelf, this would be of great importance to the research of geodynamics and ice kinematics of east Antarctica.
Additionally, this geodetic network should be combined with the geodetic network made by Australia and Russia if possible, which would unify the geodetic network in the Grove Mountains and Lambert Glacier£∫Amery Ice Shelf System in east Antarctica.

Acknowledgements

Thanks to Dr. Jiang Weiping, Zhang Hongping and Liu Youwen from GPS Center of Wuhan University for the support of GPS data processing.

5. Reference

  1. Sun JB et al. The Digital Mapping of Satellite Images Under No Ground Control and the Distribution of Landform, Blue Ice and Meteorites in the Grove Mountains, Antarctica. Chinese Journal of Polar Science, Vol.13, No.1, P. 21 31, 2001.
  2. Cheng YJ, Lu LH, Bian LG The Weather Characteristic in Summer Season in the Grove Mountains, East Antarctic. Chinese Journal of Polar Research, Vol.11, No.4, 291 300,1999.
  3. Peng WJ, Ding SJ, Chen CM The Application of Post Process DGPS Technology in the Topographic Mapping of Grove Mountains, Antarctica. Chinese Journal of Polar Research, Vol.13, No.4, P. 301 306, 2001.
  4. Gary Johnston, Paul Digney, John Manning Extension of the Australian Antarctic Geodetic Network in Grove Mountains. AGS’01, 2001.
  5. Cheng X, Zhang YM, E DC et al. The operation of GAMIT/GLOBK in PC. Bulletin of Surveying and Mapping, No.1, P. 4 6 2003.
  6. Jiang WP, Liu JN, Ye SR The analysis of the System Error in Baseline Processing of GPS Deformation network. Journal of Wuhan University, Vol.26, No.3, P.197 199, 2001.
  7. Wang QH, E DC, Chen CM Antarctic Traverses from Zhongshan Station to Dome-A and the Results Analysis for the GPS Points along the Expedition Route. Geo-Spatial Information Science, 5 (1): 31_36, 2001.