Understanding the snowmelt

Author: Renata Barradas Gutiérrez

To better understand 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.

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.

To better understand 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.

The team of researchers currently uses two Leica GS10 GNSS receivers and two CS20 field controllers to collect point type data for a wide variety of research projects. With Leica Captivate field software, the team collects and organises the data while Leica Infinity survey software is used to project and filter the collected field points, ensuring data is stored in the correct coordinate system. UAV post processing software is also used.

“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.”

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.”

Helping earth’s water mapping mission

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.

“The reliability of the rover to make quick and accurate measurements several kilometres from the base gives me confidence we will be able to validate NASA’s AirSWOT data successfully,” said Evan Wilcox, MSc Geography Candidate at Wilfrid Laurier University.

Training field researchers

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.

“Being part of a university 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.

Harsh Arctic conditions can, furthermore, push the limits of most equipment. Leica Geosystems GNSS receivers and CS20 field controllers are designed to perform in the most extreme conditions.

“The nature of our field work tests all instruments to their absolute breaking point and maximum,” said Walker. “Our Leica GNSS systems have worked in a wide range of harsh arctic conditions, including temperatures of -20° Celsius.”

Credible information on climate change

Backed up with the accuracy and precision of Leica 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.

The data generated with this research is currently being used by a wide variety of research scientists and graduate students focussing on testing and validating new data collection techniques. The information obtained also contributes to a long standing research project that collects the historical dataset for the Arctic tundra. Understanding Arctic’s hydrological processes will provide credible information on how climate change is chaining lake levels, stream flows and snow cover, and how this affects the lives of Canadians.