Understanding the snowmelt

作者：Renata Barradas Gutiérrez

由于人类活动发出的温室气体，加拿大北极地区正在经历前所未有的变暖。在过去的几十年中，西方北极特征的近地面温度显着升高，几乎是全球平均温度升高的两倍。这种变暖趋势导致了区域生态系统和在这些环境中运行的物理过程的重大变化。

为了更好的能听懂and how the Arctic tundra will respond under further climate change scenarios, members of the Marsh Lab Trail Valley Creek (TVC) research group from Wilfrid Laurier University in Canada led by Dr. Philip Marsh travelled more than 4,000 kilometres to study the changing hydrology of Canada’s western Arctic using Leica Geosystems GNSS instruments. The research collects data on all components of the water cycle and aims to understand how further temperature increases will affect the local and regional freshwater systems by combining:

• detailed field observations
• remote sensing
• GNSS positioning and modelling.

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Survey time

The annual input of water stored as snow is the most important aspect to the hydrological cycle and the largest freshwater contributor to Arctic stream and lake systems. At the end of winter, between April to mid-May, Marsh Lab TVC researchers conduct snow surveys measuring the snow depths and water storage across multiple basins of study. The group of researchers accurately measures the annual snowfall accumulated over the winter months to quantify the amount of liquid water storage, measured as Snow Water Equivalent, and to calculate the amount of water available to the hydrological system once the snow melts.

为了更好的能听懂and the heterogeneous nature of the tundra snow cover, Marsh Lab TVC researchers use many recent technological advances, including:

• Unmanned aerial vehicles (UAVs)
• aerial based snow depth data
• automated snow depth recording probes
• experimental cosmic ray neutron probe stations.

研究人员目前使用两个Leica GS10 GNSS接收器和两个CS20现场控制器来收集各种研究项目的点类型数据。借助Leica Caintivate Field软件，团队收集和组织数据，而Leica Infinity调查软件则用于投影和过滤收集的现场点，以确保数据存储在正确的坐标系中。也使用了无人机后处理软件。

“Our field work relies heavily on obtaining high accuracy spatial datasets and our Leica Geosystems GNSS system makes all of this work possible,” said Branden Walker, Research Associate at Wilfrid Laurier University. “Previously using Leica Geosystems instruments at other research sites with excellent results, we chose to go with them again for this project.”

The group of researchers also used the GS10 GNSS receivers and CS20 field controllers for regular surveying of ground control points, and surveying topographic changes for ground validations and change detections of permafrost features.

“The majority of our ongoing research projects are centred on obtaining highly precise and accurate GPS data,” said Walker. “Compared with other data sets, Leica Geosystems GNSS systems have proven to provide robust and reliable data.”

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Collecting data form above and below

One of the main methods for measuring the snow across larger areas is through the experimental use of UAVs. In order to validate, georeference and correct the GNSS data from the UAV, Marsh Lab TVC researchers need to measure the actual Snow and Ground Surface Elevation on the ground using a Leica Geosystems GNSS system for surveying ground control points with UAV mapping points with a high level of accuracy. These highly precise ground control points are then processed in Infinity survey software and a photogrammetry software to improve the accuracy of the UAV mapping points.

“The Leica Geosystems GNSS system we use allows us to create ground control points with a known position with sub-centimetre accuracy. This is very important for correcting our elevation products from the UAV, which may only differ from one flight to the next by a few centimetres,” said Walker. “This data allows us to quantify snow depth and water storage with previously unobtainable spatial and temporal resolutions. The data from our UAV is post processed and georeferenced using ground control points collected with our Leica RTK system to produce highly precise and accurate spatial datasets.

“Our Leica Geosystems instruments are the backbone of our research programme. The precision and accuracy provided by our GNSS instruments provides the spatial data required to map small scale variations in snow depth using the UAVs and helps us to save time in the field when setting up and collecting data points.”

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帮助地球的水图任务

The research conducted by Marsh Lab TVC researchers using Leica Geosystems GNSS systems will also be the main ground validation for Air Surface Water & Ocean Topography (AirSWOT) in North America, a component of NASA’s Arctic Boral Vulnerability Experiment (ABoVE). The AirSWOT validation mission measures the surface height of water on as many lakes as possible during flights. AirSWOT is part of SWOT mission to map Earth’s water from space to know how much fresh water there is on Earth and to calculate river flow rates and monitor coastal ocean currents.

NASA’s AirSWOT Phenomenology airborne radar flies across Northern Canada and Alaska measuring the Water Surface Elevation of tens of thousands of water bodies larger than 250 metres across. For the AirSWOT mission, the team has a small window to capture the measurements needed so they must have quick and reliable GNSS instruments that are capable of measuring from a long distance range from the base.

威尔弗里德·劳里尔大学（Wilfrid Laurier University）的MSC地理候选人Evan Wilcox说：“流动站的快速准确度量的可靠性使我有信心我们能够成功验证NASA的Airswot数据。”

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培训现场研究人员

Marsh Lab TVC hosts research groups from North America and Europe who study Canada’s arctic regions. Wilfrid Laurier researchers regularly help train student researchers on how to use Leica Geosystems products.

“大学的一部分sity led research group also results in a high student turn around, so the simplicity and intuitive design of Leica Geosystems products makes training the next round of field researchers and students much easier – again, saving our group time and money in the long run,” added Walker.

此外，恶劣的北极条件可以推动大多数设备的限制。Leica Geosystems GNSS接收器和CS20场控制器设计为在最极端的条件下执行。

沃克说：“我们的现场工作的性质将所有工具都带到了它们的绝对突破点和最大程度上。”“我们的Leica GNSS系统已经在各种恶劣的北极条件下工作，包括-20°Celsius的温度。”

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关于气候变化的可靠信息

备份与徕卡的准确度和精密度Geosystems, the group of researchers are gaining a greater understanding on how the Arctic tundra systems have changed in response to increased air temperatures resulting from climate change. Accurate and reliable data is needed to better understand the complex relationship between snow depth, rain, lake levels, vegetation, permafrost and streamflow, and the physical processes at play to be able to predict future changes using mathematical models.

目前，众多研究科学家和研究生正在使用这项研究生成的数据，重点是测试和验证新的数据收集技术。获得的信息还为一个长期的研究项目做出了贡献，该项目收集了北极苔原的历史数据集。了解北极的水文过程将提供有关气候变化如何封闭湖泊，溪流和积雪的可靠信息，以及这如何影响加拿大人的生活。