Reference Station user strategies in a tectonic environment

作者：Penny Boviatsou

Earthquakes are a response to the motion between tectonic plates. As two plates push together at a steady rate, the rocks along the plate boundary become more and more stressed until eventually something has to give — an earthquake occurs along a fault somewhere in the plate boundary zone.

New Zealand lies at the edge of both the Australian and Pacific tectonic plates. The Australian and Pacific plates push against each other along a curving boundary and generally don't move smoothly past each other. They move in a series of small rapid motions, each of which is accompanied by earthquakes.

年代martFix, based on the world’s largest reference station network, HxGN SmartNet, is New Zealand’s most extensive GNSS reference station network with more than 70 stations nationwide. SmartFix delivers centimetre level, real-time kinematic corrections, post processing solutions and sub-metre GIS corrections. HxGN SmartNet is an integrated 24/7 GNSS network RTK and correction service, built on the world’s largest reference network, enabling GNSS-capable devices to quickly determine precise positions.

Global Survey Limited的总监Bruce Robinson说：“通过Internet提供实时运动学（RTK）校正服务，并提供延时处理的Rinex文件，我们的客户可以享受SmartFix的好处。”“如果他们的GPS或GNSS接收器可以连接到Internet，那么SmartFix可以提供所需的数据。”

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地震摇晃新西兰

New Zealand has two types of earthquakes. Deep earthquakes under North Island form a well-defined band (seismic zone) running northeast from Marlborough through White Island. Shallow earthquakes tend to occur to the southeast of this seismic zone, while the deeper ones occur towards the northwest.

The New Zealand GeoNet, a partnership between the Earthquake Commission (EQC), GNS Science, and Land Information New Zealand, monitors all geological hazards in the country, and locates between 50 and 80 earthquakes each day – about 20,000 a year. Earthquakes can occur anywhere at any time in New Zealand.

These earthquakes are continually altering the shape of New Zealand and while a lot of the movement is small and unfelt, it is continual and the result is perceivable, measurable and locally variable. The measurable and variable part is what the reference station network SmartFix needs to deal with.

There are many examples of rapid movements that combine lateral and vertical movements. Such movements are clearly not uniformed; this variability creates challenges for those who need to establish reliable survey control or those who run reference station networks.

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研究地震活动

Even though New Zealand is continuously moving and deforming under the influence of the Australian and Pacific tectonics plates, the country’s datum is designed to provide constant unchanging coordinates for features.

Datums define how coordinates, longitudes and latitudes or heights, relate to physical locations. Projections are different ways of representing a position in a datum, for example as northings and eastings used on topographic maps. Together, they define New Zealand's coordinate systems.

To manage this deformation, the datum itself is moving and deforming along with the New Zealand land mass – it is a “plate-fixed” datum.

The New Zealand datum is known as NZGD2000, and this datum is based on International Terrestrial Reference Frame (ITRF) 1996 as at the position on the feature on January 1, 2000. Because the datum is deforming, NZGD2000 coordinates no longer reflect the true positions of points relative to one another.

但是，局部变形很小，对于大多数应用，变形可以并且被忽略。这允许直接从NZGD2000坐标计算距离，轴承和区域。但是，该变形需要由参考站管理员不断解决和管理。

自2000年以来，忽略变化的错误每年不超过一毫米。定期应用变形模型来考虑由于地震引起的变形，以计算NZGD2000坐标，并且随着变形模型的测量变得更多准确的。

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Challenges when running a reference station in New Zealand

NZGD2000基准设置为2000年1月1日 - 最后一次一切都很好地融合在一起。自2000年以来，新西兰已经进行了17。5年的差异运动，尽管商标的坐标没有改变，但相对位置却有。今天从三个不同参考站进行调查的观点可能会有三个不同的NZGD2000坐标取决于所使用的参考站。

Robinson说：“客户的教育是新西兰SmartFix管理员职位的主要组成部分，因为我们正在吸引用户来了解电台选择的大地测量含义。”

The second challenge is obtaining and choosing the two coordinates for the reference stations that the Leica GNSS Spider reference station software requires. The two coordinates being the current epoch coordinates to ensure the reliability of the network and the NZGD2000 coordinate. The GNSS Spider solution is an integrated software suite for centrally controlling and operating GNSS reference stations and networks and helping to manage complex environments such as New Zealand.

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可靠有效的解决方案

Using a network like HxGN SmartNet (SmartFix in New Zealand) saves field crews time as it precludes the setup of separate base stations, and it avoids the risk of having control fail due to a damaged or stolen base and removes the issues of radio interference. Surveyors have long used GNSS networks to save time and money as well as remove potential sources of error.

Instead of carrying around:

• GPS receivers
• batteries and cables
• two radios
• a tripod and a pole
• and setting up their own local base for each project,

network users simply carry a GPS or GNSS smart antenna (rover) with an internal modem or an external mobile phone and use that equipment to quickly access a network of permanent reference stations. The combined data from those permanent stations is used to generate RTK corrections and provide accurate positioning at much greater distances than traditional radio solutions.

Robinson说：“在《调查全球调查》中，我们致力于SmartFix（SmartNet）网络的增长。”“尽管面临构造挑战，但我们的客户能够获得可靠且可重复的NZGD2000坐标，对于用户来说，它使他们更有效，使他们可以按时并按预算完成项目。”