ASM
Rebuilding after the Great Sichuan Earthquake
ZHUANG QUINCUN, HUANG HAU and ANGI BOWMAN
Zhuang Quincun is the GPS technical manager for Wuhan Technical Center of Sokkia Surveying Instruments Trading (Shanghai) Co Ltd. He graduated from Wuhan University with a bachelor’s degree in engineering and has almost a decade of GPS and technical experience. Huang Hau also has a bachelor’s degree – from the Northeast China Forestry University. He has more than a decade of surveying experience and currently works in the marketing department as the GPS Sales Manager for Sokkia. Angi Bowman is the marketing and communication specialist for Point Inc. She holds a degree in communications from Ottawa University.
On 12 May 2008, the earth beneath the Sichuan Province of western China shifted. It generated a massive magnitude 8.0 earthquake. The three minute earthquake was felt throughout China and Southeast Asia, but the Sichuan Province was hardest hit.
The earthquake, combined with aftershocks and landslides, reduced millions of businesses, homes and schools to rubble. Almost 80,000 residents lost their lives, and 360,000 were severely injured. Millions of residents lost everything.
But hope springs eternal. The minds of government leaders soon turned from helping those affected, to rebuilding their communities. Recently, we joined with the Hebei Bureau of Surveying and Mapping in a project to rebuild six villages in PingWu County, near the epicentre of the quake.
Less than two months after the earthquake, two teams from the bureau travelled to the disaster area to re-establish crucial boundaries and control points in the county. The six villages were PingTong, DouKou, GuCheng, ShuiJing, GaoCun and BaZi. Once control points were established and parcel boundaries re-surveyed, the process of rebuilding the villages could proceed.
Transportation lines to and from Sichuan had been severed by the earthquake, but they had been rebuilt to allow the immediate relief efforts. The teams travelled 2000 kilometres to reach PingWu County. It took two days of driving -- in three jeeps and one van.
Once in the villages, team members were overwhelmed by the magnitude of the destruction. Tian Zhi, the director of the bureau's technical department, said: 'We were all shocked by the disaster. Most of the buildings were broken. Even though we all had seen the images of destruction in the newspapers, nothing could have prepared us for what we saw when we arrived'.
Before surveying could begin, the teams had to meet four specifications laid down by the bureau. First, the surveys should be completed using the local co-ordinate system. This presented a problem. Normally, the reference location for the local datum is at the centre of PingWu County. But it was the region hardest hit by the earthquake, and re-establishing a reference station there would take too long.
Software from Sokkia -- the SDR+ Coordinate System Manager – was pressed into service. It can convert data between various datum and co-ordinate systems, including accepted user defined projections.
We created a user defined system, based on the Transverse Mercator projection, to meet the needs of a local co-ordinate system. The team used the reference datum WGS84, and the Bursa Wolf transformation method for accurate co-ordinate transformation.
The second requirement was to establish an RTK network to cover the area. A receiver capable of performing long baseline RTK (our requirement was 40 kilometres) was needed.
We used Sokkia's GSR2700 ISX and its AdVance RTK capability. Its baseline range extended beyond 40 kilometres, providing enhanced accuracy and reliability while meeting the HBSM criteria.
Another advantage of this device is its ability to receive both GPS and Glonass satellites. The Sichuan Province is far from the ideal location for performing a GNSS survey. The Himalayan mountains lie to the west, the Qinling Range is to the north, and the mountains of Yunnan lie south. This limits the number of satellites that can be tracked, which decreases the accuracy of the data collected. However, the more satellites the better, so the addition of Glonass satellites to the usual GPS fix was welcome.
'The satellite geometry, for the most part, was not favorable,' said Zhi. 'Nevertheless, we tracked an average of six to eight satellites. We were able to complete all surveys in just a week when the job could have taken months.'
It was also essential that the same RTK reference point could be accessed by several survey crews with different equipment. Sokkia’s Mobile Reference Station system was set up on-the-fly to meet the short term needs of this survey for localised RTK coverage. RTK data was distributed in standard correction formats, supporting our own receivers and receivers from other manufacturers as well.
Finally, the bureau noted that because of the mountainous surroundings, a GPS receiver with excellent tracking ability was necessary. The GSR2700 ISX is ideal for this because of its 72 GNSS channels, designed so that it can potentially receive signals from all the GPS and Glonass s satellites at the same time..
One of the receivers was positioned in PingWu County and established as a Mobile Reference Station. Team members were then able to stream data from rovers over a GPRS connection to another reference station in Wuhan, more than 900 kilometres from PingWu.
This station, acting as a mainframe, then managed the data and distributed it to rovers within the 5000 square kilometre working area of each Mobile Reference Station. Villages being surveyed were located in an 80 kilometre area. Although any number of rovers can be supported by a Mobile Reference Station, the teams used four.
Many communications and electrical lines had been severed by the quake. As a result, all the units operated using batteries and wireless connections.
The project successfully reached all its goals. Reconstruction in the villages has begun.
