2Key Laboratory of Polar Surveying and Mapping, SBSM, Wuhan 430079, China
0 IntroductionAntarctic surveying,mapping and remote sensing integrate modern geodesy,remote sensing,digital mapping,geo-graphic information systems and related disciplines such as glaciology,oceanography,geology and environment sci-ences. This work aims to study Antarctic plate motion,de-scribe topographic characteristics of the surface,monitor ice-snow-ocean dynamic processes,and build a digital po-lar framework using the spatial data and information. Therefore,this is a relatively new domain of study in Chi-nese polar science that builds on modern surveying science and spatial information technology.
Surveying and mapping for Chinese Antarctic expedi-tions have two main functions. One is to provide technical support for the expedition,including the provision of all sorts of maps and spatial geographic information platforms,etc. The other is to study changes in the polar environment (e.g.,through mass balance) using modern surveying tech-niques. At the same time,because of the attributes of the surveying on the Antarctic continent per se,such as ex-panding map coverage,establishing ground control points,and the naming of geographic entities,the surveying and mapping has great significance for the maintenance of na-tional rights and interests.
During the austral summer of 1984/1985,the first Chinese Antarctic National Research Expedition (CHI- NARE) established the Great Wall Station in West Antarc-tica and began an ongoing program of surveying and map-ping that has been supported by the State Bureau of Sur-veying and Mapping (SBSM) and the State Oceanic Ad-ministration (SOA). Advances in science and technology have led to the need to update traditional surveying meth-ods to global Earth observations based on GPS,RS and GIS techniques. Great progress has been made in geodesy,en-vironmental remote sensing,digital mapping and internet spatial information techniques in Antarctica.1 GeodesyGeodesy is the scientific discipline that deals with the study of the shape of the Earth and its motion. In the history of Antarctic research,the work of geodesists has led to the establishment of the coordinate system,the application of GPS technologies,and investigations of the gravity field,the geoid,crustal motion,and sea level change,etc. 1.1 Early Chinese geodetic work in AntarcticaDuring the 1984/1985 austral summer season,China carried out the first Antarctic expedition and built the Great Wall Station in the King George Islands,West Antarctica. The first and foremost task undertaken was to accurately deter-mine the location of the station. The TRANSIT system,also known as NAVSAT (Navy Navigation Satellite System),was used to determine the coordinates of the Great Wall Station: 62°12´59"S,58°57´52"W,in the WGS72 system. The height system of the Great Wall Station area was estab-lished using a tide staff. Using traditional astro-geodetic surveying and gyroscopes,the orientation of the meridian was measured,and the coordinate system of the Great Wall Station was thereby established. Based on the geodetic da-tum,the distance and azimuth from the Great Wall Station to Beijing were calculated. At the same time,an engineer-ing construction survey and lay out were undertaken[1, 2, 3, 4, 5]. In 1989,when the second Chinese Antarctic station—Zhong- shan Station was established in the Larsemann Hills,East Antarctica,the same methods were used to build the coor-dinate system and undertake basic survey tasks.
From the late 1980s to the early 1990s,based on the techniques and funding available at that time,a geodetic control network was established,and relative gravimetry measurements,mapping etc. in the vicinities of the Great Wall and Zhongshan Stations were carried out by traditional methods. These activities initiated Chinese surveying in Antarctica and laid a good foundation for later geodetic studies across the continent.1.2 Antarctic geodesy and crustal movement based on modern spatial techniquesWith the development of modern surveying techniques,especially the Global Positioning System (GPS),the coor-dinates of any point on the Earth could be obtained con-veniently and efficiently. Since 1993,GPS techniques have been applied in Antarctica by Chinese surveyors. 1.2.1 The geodetic control networkBefore 1991,the geodetic control networks at the Great Wall and Zhongshan Stations were established by tradi-tional ground traverse survey techniques. The control net-works satisfied surveying and mapping requirements during that period. Since 1991,with the rapid development of GPS techniques,the geodetic control networks at the Great Wall and Zhongshan Stations,the Grove Mountains and Dome Argus (Dome A) were established one after the other. The coordinate systems for Chinese Antarctic expedition areas were united with the world geodetic system. 1.2.2 Crustal movementDuring the austral summer of 1985/1986,a two-dimen-sional (2D) monitoring network was built in the vicinity of the Fildes Strait fault zone,West Antarctica,consisting of infrared laser ranging. In 1991,the monitoring network was updated to a three-dimensional (3D) monitoring network using GPS technology.
In the 1990s,GPS technology began being widely used in Antarctica. In 1994,the Geoscience Standing Scien-tific Group (GSSG),which is the former Working Group on Geodesy and Geographic Information (WGGGI) of the Scientific Committee on Antarctic Research (SCAR),car-ried out the Epoch GPS Campaigns. The GPS campaigns provided a valuable data set that is used to link Antarctica with the International Terrestrial Reference Frame (ITRF),and to gain the first detailed insights into the tectonic be-havior of the Antarctic plate. The observation period of the GPS campaigns was between 20 January and 10 February each year. A tracking rate of 15 s was recommended to all participating countries. The minimum cut-off angle was set to 10°.
In 1995 and 1997,the Chinese Great Wall and Zhong-shan Stations were involved in the GPS campaigns respec-tively. In 1997 and 2008,respectively,Zhongshan and Great Wall Station were rebuilt to permit year-round GPS data collection. Based on the multiyear GPS data,the hori-zontal velocity field of Antarctica was calculated (Figure 1).1.3 Gravity measurements and height datumGravity data are indispensable for the study of the gravita-tional field and the shape of the Earth. The height datum plays a key role in many studies involving gravitation such as the development of a sea model of the South Ocean and the calibration and validation of altimetry data. However,because of the extreme climate and special geographic lo-cation,gravity measurements are difficult to be deployed in the Antarctic. 1.3.1 Gravity measurementsDuring the late 1980s and the early 1990s,relative gravity measurements were made at the Great Wall and Zhongshan Stations by the Institute of Geodesy and Geophysics (IGG). Because there were no absolute gravity sites at the Chinese stations,high accuracy absolute gravity results could not be obtained. In January 2005,absolute gravity measurements were finally made at the Great Wall Station using an FG5 absolute gravimeter. At the same time,relative gravity measurements were deployed using Lacoste relative gra-vimeters at the Korean King Sejong Station and the Chilean Frei Station. In January 2008,three absolute gravity sites were measured using an A10 absolute gravimeter at Zhongshan Station,and a relative gravity network was set up in the Larsemann Hills of East Antarctica. The absolute gravimetry in Antarctica provides the gravity datum for aerogravity surveys,ocean gravity surveys and the gravity field studies[16, 17]. 1.3.2 Height datumA tide gauge was used to measure tides and also was the basic tool used to determine the height datum. In 1999,a pressure tide gauge was set on the sea bottom near Zhong- shan Station,shared and jointly operated by Australia and China. In 2009,a new tide gauge was set up by China at Zhongshan Station using Norwegian Aanderaa equipment.
The geoid is the equipotential surface that would coin-cide exactly with the mean ocean surface of the Earth. In Antarctica,some countries routinely substitute a mean sea level derived from a tide gauge for the geoid to build their local height systems. Because the datum in each of the height systems corresponds to a different equipotential sur-face,there are height differences among the height systems. It is now very desirable to unite the various elevation sys-tems of the Antarctica.1.4 GPS applications in the atmosphereBased on GPS data from the Zhongshan and Great Wall Stations,atmospheric characteristics such as meteorologic parameters and the spatial and temporal characteristics of the ionosphere have been obtained. 1.4.1 GPS applications in troposphere studiesGPS technology has been used in meteorological research work in recent years. The data from the SCAR Epoch GPS campaigns,including data from the Great Wall and Zhong- shan Stations,were used to construct the GPS network. A high accuracy software package—GAMIT/GLOBK—has been used,and multiple schemes were adopted to obtain such properties as the tropospheric zenith all delay,zenith dry delay,atmospheric Precipitable Water Vapor (PWV),and zenith wet delay. The weather characteristics of the Great Wall and Zhongshan Stations can be extracted from the above analyses. For example,the PWV series from the Great Wall Station usually increased to 20 mm rapidly,with the precipitation occurring over 3-4 h. On the other hand,the PWV series from Zhongshan Station usually showed small and slow changes,which means that there are fewer opportunities to observe precipitation at Zhongshan Station. The results agree well with in situ meteorologic observations1^. The conclusion can be drawn that GPS meteorology is a feasible and useful complement to weather forecasts in Antarctica. 1.4.2 Polar ionosphere characteristic studyPrecise ionosphere Total Electron Content (TEC) values are derived from the GPS data from Zhongshan,Great Wall and Yellow River Stations. The characteristics of TEC associ-ated with solar activities,the geomagnetic environment,and daily,annual and seasonal TEC variations have been stud-ied. 1.5 Glacier movement studiesThe Antarctic ice-sheet stores the majority of the Earth’s freshwater,with the icecap containing almost 90% of the world’s ice. As a result,changes in the mass balance of the Antarctic ice sheet would affect global sea level and global climate. Surface topography,ice velocities and height are important parameters for mass balance studies. In particular,investigations of glacier movement and dynamics based on spatial geodesy have been an area of great interest in Ant-arctic studies. Since the 1990s,ice velocities have been monitored along a traverse from Zhongshan Station to Dome A and the Amery Ice Shelf,East Antarctica. The ice velocities at the front on the Amery Ice Shelf vary from 800 to 1 200 ma-1,with the flow directions pointing to the sea. The ice velocities along this traverse are shown in Figure 2. Horizontal ice velocities increase from the summit of the ice sheet to the coast. Near the dome area,the velocities are less than 10 m·a-1; in the plateau area,the velocities range from 8 to 24 m-a"1 and reach about 98.2 m·a-1 at a site (LT980) near the coast. The flow directions are roughly perpendicular to the contour lines of the ice sheet,mostly pointing toward the Lambert Glacier Basin[24,25,26]. 2 Earth observation techniques in Antarctic studiesThe establishment of the first meteorological satellite,launched by USA in 1960,marked a new period in the era of Earth observations. Over the last 50 years,Earth obser-vation techniques have developed rapidly. Many techniques can now provide multi-spatial and/or multi-temporal reso-lution data quickly and accurately. These new techniques provide abundant data and information that cannot be ob-tained from terrestrially-based surveys and,of relevance to this paper,promote understanding of the Antarctic. Chinese scientists have used remote sensing and aerial photogram- metry techniques to map and study the dynamic process of the Antarctic. 2.1 Remote sensing and aerial photogrammetry mapping in AntarcticaTopographic maps and small-scale image maps have been made using remote sensing and aerial photogrammetry methods for the foundations of the Great Wall,Zhongshan,and Kunlun Stations and also for the Chinese inland ice sheet expedition.
(1) A small format aerial photograph technique was developed to produce a topographic map of the Larsemann Hills at 1 ! 10 000 scale. A helicopter was used as the plat-form for a non-metric 120 camera used to take pictures. The method proved to be successful in Antarctica.
(2) Large range image maps from Chinese Antarctic expedition areas were made using the no ground control point method.2.2 Applications of Earth observation techniques in the snow and ice studiesWith advancements in science and technology,techniques used for Earth observation have proven to be enormously advantageous in snow and ice studies associated with the main Chinese expedition areas (i.e.,the Great Wall,Zhongshan,and Kunlun Stations,along with the Grove Mountains and Amery Ice Shelf). Progress has been made in the aspects that follow[31, 32, 33, 34, 35].
(1) Satellite remote sensing has been applied to study glacier dynamics. The dynamic processes of the Polar Re-cord and Dark glaciers were determined from multi-period satellite images covering 17 years.
(2) The interferometric synthetic aperture radar (In- SAR) technique was used to build a digital elevation model (DEM,Figure 3),and retrieve the distributions of blue ice and ice crevasses.
(3)A satellite laser ranging technique was used to build the DEM of the ice sheet. The precise DEM along the traverse from Zhongshan Station to Dome A was built from the ICESat/GLAS data. The elevation variation of the Lambert Glacier—Amery Ice Shelf System was also calcu-lated from the ICESat/GLAS data (Figure 4).
(4) The mass balance of Antarctic ice sheet and its contribution to global sea level change was assessed from the Gravity Recovery and Climate Experiment (GRACE) data (Figure 5).
(5) The ice velocities of the Lambert Glacier—Amery Ice Shelf System were calculated from a Landsat 7 ETM+ image and an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image.3 Digital cartographyPolar digital cartography is one of the branches of polar geosciences that plays a key role in polar expeditions. It is linked closely with geodesy,remote sensing and geography. Since 1984,more than 40 Chinese Antarctic maps covering approximately 200 000 km2 have been published. More than 300 Chinese Antarctic place names have been re- leased，[36,37,38,39]. 3.1 Multi-type,multi-scale maps covering all Chi-nese Antarctic expedition areasIn 1984,during the first Chinese National Antarctic Scien-tific Expedition,the first Chinese Antarctic map—the Great Wall Station map—was surveyed,and the first Chinese Ant-arctic place name—Great Wall Bay—was named. In 1987,a topographic map of Fildes Peninsula,King George Is-lands was surveyed by aerial photogrammetry. In 1992,the Larsemann Hills image map was made using the small format aerial photograph technique. In 1999 and 2005,to-pographic maps of the core areas of Grove Mountains and Dome A were surveyed using differential GPS methods. So far,more than 40 maps covering polar areas have been re-leased,including Fildes Peninsula,Larsmenn Hills,Grove Mountains,Dome A,Great Wall Station,Zhongshan Station and the transect from Zhongshan Station to Dome A. 3.2 From simplex to multi-function mapWith the development of the Chinese Antarctic expedition,series of maps such as thematic maps,evaluation maps and dynamic maps were compiled. Representative maps include: Great Wall Station—Fildes Peninsula—King George Island maps,Zhongshan Station—Xiehe Peninsula—Larsemann Hills maps,distribution maps of blue ice and meteorite lo-cations in the Grove Mountains,and geology,geomorphol-ogy,and environmental frangibility maps of the Fildes Peninsula. 3.3 From paper to electronic mapsWith the development of digital mapping,the quantity and quality of polar maps has greatly improved. Map services have changed from classic paper maps to four-dimension products,multimedia electronic maps,navigational elec-tronic maps,online map services,etc. Products mainly in-clude bipolar multimedia electric maps. For example,the transect from Zhongshan Station to Dome A can be navi-gated solely with electronic and online polar maps. 3.4 Methods and techniques of mapping changed from classic to full digital methods based on GPS,RS and GISPolar cartography has experienced the transition from hand mapping to remote sensing mapping and computer-aided drawing. Information sources for polar cartography have increased; however,the automatic degree of polar cartog-raphy has also improved,the period of time required to un-dertake polar cartography has shortened,and the quality of polar cartography products is improved remarkably. Car-tography techniques based on the color map of desk pub-lishing technology and map visualisation based on GIS technology are of special interest. 4 Geographic information system (GIS) studiesThe development of GIS has been quick and was readily applied in Antarctic studies. In 1999,a Chinese inter-net-based prototype system for Antarctica GIS was estab-lished by the Chinese Antarctic Center of Surveying and Mapping at Wuhan University. In July 2000,the King George Islands GIS workshop,sponsored by SCAR WGGGI,was held at Wuhan University. Considering the rapid development of Chinese GIS studies,a Chinese internet GIS workshop,sponsored by the Chinese Arctic and Antarctic Administration (CAA) was held at Wuhan University in October 2002. The Chinese Polar Scientific Expedition management Information System,based on a GIS platform,was approved at this workshop.
In May 2004,a second SCAR WGGGI GIS workshop was held at Wuhan University. Experts from the USA,Canada,Germany,Italy,Poland and Russia attended the workshop. In 2006,Chinese representatives provided the geospatial information portal service for the Grove Moun-tains project. In 2009,the Prydz Bay,Amery Ice Shelf and Dome A Observatories program (PANDA) GIS system was developed by the Polar Research Institute of China and Wuhan University. The information system enabled 3D visualization of the Chinese Antarctic stations,route lines and resource distributions. Many kinds of spatial data in-eluding control points,raster maps,vector maps,3D archi-tecture models,remote sensing images and DEMs are inte-grated into the information system.
In general,Chinese Antarctic GIS integrates spatial data,application models and network services. The in-ter-operational Antarctic spatial information infra-structure has been developed step by step,providing information for Antarctic mapping,expedition management,and scientific studies. The current advances in digital Earth data are lead-ing to the developmental changes in GIS from 2D to multi-dimensional. New group software technologies,net-work technology,multi-dimensional expressions,and dis-tributed data support will be the main themes of GIS in the near future.5 ProspectsAccording to the medium and long term plans of Chinese Antarctic expeditions,we should aim to be at the frontier of international polar science,make use of the most advanced techniques of modern surveying,mapping and remote sensing,exploit a wide range of study areas and applica-tions,and be innovative in new peripheral disciplines and cross disciplines. The key goals are as follows.
(1) Develop technical systems for basic surveying and survey engineering in Antarctica.
The integration of aerial,space-based,and ground- based observation systems should be emphasized to provide efficient,quick mapping and a platform of shared services.
(2) Strengthen physical geodesy and geodynamics in the Antarctic.
A high-precision geodetic reference system in Chinese polar expedition areas should be established and linked with the ITRF. The precise geoid of Antarctica and the rela-tionship of the ice load to the characteristics of polar to-pography should be studied based on continuous GPS data,absolute and relative ground gravity data and aerogravity data. Further study is also needed in satellite orbit determi-nations and orbit reverse issues,GPS applications in the troposphere and ionosphere,and Antarctic Plate motion. For example,based on GRACE satellite gravity data,we can understand the mass balance of the Antarctic ice sheet more clearly than before[44, 45].
(3) Develop a sea surface topography model and monitor variations in the Southern Ocean.
A digital sea surface topography model of the South-ern Ocean can be used to monitor and evaluate sea level change around Antarctica. Improvements to such a model could be established by multi-satellite altimeter data and tide gauge data. With the development of Earth observation techniques,available data covering Antarctica are becoming more and more abundant. Among other things,this can support the development of a high-resolution sea surface topography model to monitor the mass balance of the Ant-arctic ice sheet and study Southern Ocean dynamics.
(4) Monitor and assess high-resolution snow and ice environment and ecology at a range of temporal and spatial scales.
The cryosphere in the polar regions is closely related to global climate and environmental change. Through the latest Earth observation techniques,using multi-source spa-tial data,variations in the ice environment and mass bal-ance can be monitored and a digital 3D terrain model could be established.
Because of its extreme location and climatic charac-teristics,the Antarctic environment is transitional,fragile and sensitive. The activities of human beings in Antarctica have a significant effect on the fragile Antarctic ecology and environment. So,we plan to establish monitoring areas in East Antarctica to measure such effects.
a) The monitoring areas include Zhongshan Station,the Grove Mountains,Amery Ice Shelf,Dome A and all of the Chinese expeditions in East Antarctica.
b) The monitoring objectives include ice sheets,ice shelves,glaciers,coastlines,the geoid,subglacial lakes,and subglacial topography.
c) The technical systems used for monitoring are based on a modern integrated technical platform. They include satellite-based platforms,airborne radar,airborne laser ranging,airborne gravity,and ground-based 3D visualiza-tion survey platforms. Observations of periodic,operational and secular data should: (i) improve the temporal and spa-tial resolution of the monitoring data sets,(ii) enable the establishment of an Antarctic environmental information monitoring system framework,(iii) accumulate Antarctic ecological and environmental information,(iv) obtain key parameters of environment change,(v) describe the rules of dynamic variation in the Antarctic environment,and (vi) provide a scientific foundation for Chinese ecological and environmental protection and management.
(5) Build a ‘Digital Antarctica’，by establishing a polar spatial information grid sharing on a global scale.
The sharing of information will be a key part of future Antarctic expeditions involving multiple countries and mul-tiple crossed disciplines. Grid techniques will make the sharing and integration of information possible. The func-tions of Digital Antarctica are to:
a) Integrate environmental change parameters,describe the polar dynamic variation quantitatively and solve scien-tific problems.
b) Facilitate data acquisition and sharing,and provide a scientific platform for multi-disciplinary teams who ob-tain polar data and resources and analyze polar environ-mental changes.
c) Provide the management and decision support for responsible departments and agencies,provide more scien-tific and efficient survey support,and share GIS services for Chinese polar expeditions.Acknowledgments We thank all of the members of CHINARE who have made contributions to the Chinese Antarctic surveying,mapping,geoinforma-tion and remote sensing since 1984. This study was supported by the National Administration of Surveying,Mapping and Geoinformation (Grant no- 1469990324229),the National Natural Science Foundation of China (Grant nos.40806076,41176172,41176173),the National High Technology Research and Development Program of China (Grant no. 2008AA121702-5),the National Science and Technology Infrastructure Program of China (Grant no.2006BAB18B01) and the Chinese Arctic and Antarctic Administration,SOA(Grant no. 20070206).
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