Northern Ireland’s Strangford Lough is the largest, most ecologically diverse inlet in the British Isles. But an invasive alien grass species called Spartina anglica is threatening the region and potentially impacting feeding habitats for thousands of wildfowl and waders. One survey company precisely mapped Spartina’s reach, enabling authorities to develop a mitigation plan to help preserve the Lough.
HeritageNI founder David Craig using Trimble Catalyst in Northern Ireland’s Strangford Lough.
Any hope for mitigating Spartina’s spread starts with having a precise picture of its prevalence—something the National Trust and the Northern Ireland Environment Agency (NIEA), key managers of the area, didn’t have.
To remedy this, the National Trust, supported by the NIEA, contracted HeritageNI, a drone and mapping company based in Northern Ireland. Together with Allen & Mellon Environmental, the company was charged with mapping the distribution of Spartina along the lough’s more than 150-kilometer intertidal area.
HeritageNI originally planned to conduct the survey via drone. Equipped with a 20-mp Hasselblad camera, the company’s drone had the necessary resolution to capture the spectral signature of Spartina’s specific shade of green. The problem, however, was that the technique struggled to identify Spartina when it decays and becomes brown. This meant that, using drone imagery alone, HeritageNI would have missed the very small, single outbreaks happening in the middle of these natural salt marsh areas.
As a result, it was decided very early on that the trained eye was the best method for identifying all Spartina outbreaks. Of course, this meant heading out on foot. And in a region notorious for short days, cold winters, lots of rain, varying tides, and hundreds of kilometers of challenging terrain—this was no easy feat.
To succeed, the company needed a versatile surveying solution that was light to transport, easy to use, and capable of providing the precise level of accuracy the project required. HeritageNI chose the Trimble Catalyst solution.
HeritageNI has registered more than 30,000 GNSS data points along the lough’s shoreline.
ACCURACY, SPEED AND PRECISION
Trimble Catalyst is a subscription-based GNSS solution offering professional-grade positioning as an on-demand service. Its easy-to-use, lightweight, plug-and-play USB antenna, and smartphone compatibility, made the Catalyst particularly convenient for visually inspecting the shoreline on foot.
“We already used Catalyst when plotting ground control points to use in our originally planned mapping by drone, so we were aware of the lightweight nature of the system and found it ideal for this new task,” said HeritageNI founder David Craig.
Over the past year David has registered more than 30,000 GNSS data points along the lough’s entire shoreline—using Catalyst for the clumps along the perimeter identified by eye and by drone for the larger swaths located in salt marsh areas.
Northern Ireland’s Strangford Lough is the largest, most ecologically diverse inlet in the British Isles.
After entering the collected GNSS data points into the previously installed Trimble UAV Ground Control app, David sent the data by email as a CSV attachment and then imported it as a layer in Quantum GIS (QGIS). Next, the points were hand digitized on a separate overlaid polygon shapefile (.shp) layer. The polygon points in the CSV file were then removed and the remaining points merged into a global shapefile layer containing just single points.
The resulting dataset contained two shapefiles, one with points representing single plants or small clumps less than 0.5m2 and the other with polygons of the larger clumps. The area of these clumps is automatically calculated and stored in the attribute layer of the shapefile.
The data files were then turned over to the National Trust and the NIEA. “Having a very accurate picture of nearly every occurrence of Spartina in the lough means these organizations can prioritize their mitigation efforts and, hopefully, preserve this important habitat for generations to come,” said David.
“Location accuracy, data acquisition speed (within 15 seconds), as well as the ability to identify even a single plant, are the main advantages of using Catalyst.” — David Craig, founder, HeritageNI