China: Tour against the current

China: Tour against the current

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RTK GNSS receivers turned out to be the ideal surveying equipment while building water infrastructure in the hostile Nu River Grand Canyon in China

Nu River Grand Canyon is located in north-west of Nu River State, Yunnan Province, China. This 300 km-long canyon has an elevation of 3000 metres and the fall from mountain top to river surface of most section is over 2000 metres, deeper than the famous Colorado Grand Canyon.

This depth makes Nu River Grand Canyon seldom visited and it is titled “Eastern Grand Canyon”. The local government is making investments to build water infrastructure in the Canyon. But in the preliminary, pre-construction measurement stage, they faced a number of challenges. These included high humidity levels, significant temperature changes and low temperatures over long periods. These challenges made it impossible to use conventional survey instruments, necessitating the use of efficient GNSS equipment.

The government selected Kolida K9T RTK GNSS receivers. K9T can receive signals from GPS and GLONASS systems and acquire positioning information in real time with accuracy that can reach 8mm+1ppm. The utility software for topography measurement and water path grid design on controller enabled surveyors to do office work the in field.

After basic operation training, the surveyors began the tour against the current of Nu River. The actual environment turned out to be more complicated than expected: cliffs besides the narrow muddy path, heavily covered sky and sudden cold rain, the minimum temperature dipping to fifteen degree Celsius below zero. The surveyors” team set the base station on the mountainside and mountaintop as well, extending the pole of rover up to over 2.5 metres to ensure that it could receive the correction signal from the base station. The work team moved between the mountaintop and the foot of the mountain to seek a control point.

During the day-long measurement process, the government realised that it was a wise decision to use GNSS receivers as they delivered the desired results. Satellite signals could be received just after switching the power on; within 20 seconds the float data became fixed. Under the guarantee of two units 2500mAh batteries, the instruments worked continually from noon to 9 p.m. RTK GNSS receivers also offered benefits like several rover stations working together at the same time after the base station is set, with rapid initialisation and getting fixed data immediately.