Susan Smith has worked as an editor and writer in the technology industry for over 16 years. As an editor she has been responsible for the launch of a number of technology trade publications, both in print and online. Currently, Susan is the Editor of GISCafe and AECCafe, as well as those sites’ … More »
WingtraOne and Septentrio GNSS Receivers Team Up to Provide 3D Positioning Accuracy for Avalanche Prevention
November 7th, 2019 by Susan Smith
Avalanches can be extremely dangerous especially for off-piste skiers as well as for small towns situated below the slopes. As ski season comes upon us, it’s a good idea to check the avalanche conditions of the ski slopes you plan on frequenting. There are over 1000 avalanches occurring every year in the Swiss Alps alone. Local communities put up steel fence barriers along the slopes to prevent avalanches from encroaching near their town. To build such snow barriers, steep rock faces and cliffs need to be surveyed with utmost precision.
Swiss-based survey and mapping company Darnuzer Ingenieure AG has the expertise in surveying snowy peaks such as those above the famous resort town of Davos, located in the Swiss Alps near the Austrian border. Above the city, towers the magnificent Schiahorn mountain, its slopes lined with pistes and chairlifts. To protect the town and the skiers, Davos community plans to build avalanche barriers along the steep slopes. The ideal location is along one square kilometer on the Parsenn slope, right above a ski piste. To plan the works along this uneven rock face, a detailed 3D reconstruction of the area is needed. Their WingtraOne, fixed-winged drone features a top-quality camera, combined with a Septentrio high-performance GGNSS receiver,* according to company materials. It can fly at 150 m altitude making orthophotos without the need of GCPs (Ground Control Points) or a real-time base station link. GCPs are markings on the ground with a known location, used as a positioning reference when making orthophotos. Placing GPSs on the ground is time consuming work. Darnuzer’s surveyors can get their job done over 4 times faster with the Wingtra drone where no GCPs are required. After a couple of hours of flight, the survey job is done.
“Even in the valleys where satellites visibility is low, we always get the positioning we need due to the receiver having access to several navigational satellite systems. The positioning accuracy we are looking for is generally 2-5 cm,” says Dr. Bruno Wirth, senior surveyor at Darnuzer Ingenieure AG. “The Wingtra system has worked out-of-the-box and we have never had any issues with interference thanks to Septentrio’s GNSS* technology.”
The wide-open space between the peaks provides few barriers for radio waves, which might be broadcast by near-by communication towers. Such radio waves also known as Radio Frequency Interference (RFI) can overpower GNSS satellite signals and interfere with GPS receiver operation, reducing accuracy or even causing loss of positioning. Robust interference mitigation technology is key to ensuring continuous and trustworthy positioning of the GNSS receiver.
Maria Simsky, Technical Writer, Septentrio answered some questions for GISCafe Voice about Septentrio’s high performance GNSS receiver and post-processing engine GeoTagZ.
1. What is the accuracy of a drone compared to the GCP coverage?
2. What is an intuitive Wingtra workflow?
The WingtraOne VTOL drone Vertically Takes-Off and Lands on a rocky slope and flies automatically, meaning no drone pilot training required and no risk of damaging the payload with “belly” landings. A single surveyor takes the drone to the rocky Parsenn slope during the summer season, capturing ground images without snow needed for the 3D model. As the drone flies, it takes high-resolution images which are immediately geotagged and time stamped. Darnuzer’s surveyors then post process the images for RTK (Real Time Kinematic) centimeter accuracy using the intuitive Wingtra workflow, powered by the Septentrio post-processing engine GeoTagZ. The orthophotos are then processed by Pix4D software and a detailed 3D Digital Terrain Model (DTM) of the Parsenn slope is created.
First images are taken with the drone without GCPs or base-station link. Then GNSS post-processing it done with GeoTagZ to achieve RTK cm-level accuracy. Then Pix4D software is used to stitch the orthophotos together and to create the 3D model of the area.
3. Explain the positional accuracy in the mountains.
4. How does the interference mitigation technology work?
Narrow-band interference can be caused by electronic devices and effects only a small portion of the GNSS frequency spectrum. To mitigate the effects of narrow-band interference, 3 notch filters can be configured either in auto or manual mode. These notch filters effectively remove a narrow part of the RF spectrum around the interfering signal. The L2 band, being open for use by radio amateurs, is particularly vulnerable to this type of interference. The effects of wideband interference, both intentional and unintentional, can be mitigated by enabling the WBI mitigation system. The WBI system also reduces, more effectively than traditionally used pulse-blanking methods, the effects of pulsed interferers.
5. Explain why you are doing tree and rock removal. Is this used for stone avalanches as well?
6. How is ground movement monitored?
Snow avalanches are not the only type of avalanches posing danger in the steep Alpine mountains. Stone avalanches and landslides are just as hazardous. The Val Bruna is a steep, rocky slope rising above the ski resort village of Müstair. Heavy rainfall erodes the soil, creating a potential landslide threat. Every year Darnuzer’s WingtraOne drone flies over the Val Bruna slope surveying soil movement. Precise measurement of ground movement is key in helping experts asses the risk of landslides in the coming year.
*GNSS refers to Global Navigation Satellite System such as the American GPS, Russian GLONASS, European Galileo, Chinese BeiDou. These satellite constellations broadcast positioning and timing information which is picked up by the a GNSS receivers on Earth and used to calculate its global position.
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