Blog - Kieran Craven – CHERISH Geological Survey Ireland Project Manager

No rain and wind gusts less than 10 m/s.

This is what is required for unmanned aerial vehicle (UAV) surveys. The rain obscures the camera (and could damage it), while the wind affects the stability of the UAV, resulting in blurry images (never mind the potential for crashing!). UAV surveying is all about watching three or four weather forecasts and looking out for those sweet spells of suitable conditions.

We managed to get out for one day in December 2019 and felt blessed to get the opportunity. Otherwise it’s been a succession of storms waiting to hit Ireland.
Until lockdown of course. Now every forecast seems like that below. Four full days of ideal weather conditions for southeast Ireland, a blustery Sunday, then a return to settled weather.  Frustration is an understatement!

 Weather forecast

After a winter of storms, it would be great to get out and assess the change that has occurred. We’ve been using Cloud Compare to assess change, and have successfully applied it in Rosslare, Co Wexford. Now we’re keen to return to our other sites to collect a time series of data to assess the change.

Assessment of change in Rosslare 2017-2019

 Assessment of change in Rosslare 2017-2019 (Red = erosion, Blue = deposition)

We’ll just have to wait…

In the meantime, we’ve been busying ourselves with re-processing our previously acquired data. By altering the processing camera parameters for our eBee fixed wing, we’ve been able to improve the accuracy of our digital surface models (DSMs) relative to our field checkpoints. This also appears to improve the fit of adjacent flights. We’ve standardised our approach to apply for future flights (fingers crossed for 2020).

We’ve also used the time to merge our onshore and offshore data sets. Puffin Island (off Anglesey, Wales) is our most complete data set, so we’ve started here. Airborne LiDAR (0.25 m resolution), procured early in CHERISH by the RCAHMW has been merged with multibeam bathymetry (2 m resolution) collected by the Geological Survey in 2018 using the RV Keary. We’ve used Arc GIS for merging and the results look good. It gives a complete record of the island in its regional setting at the mouth of the Menai Strait.

Multiple hillshade image of merged seamless map of Puffin Island

Multiple hillshade image of merged seamless map of Puffin Island

We’ve imported this into 3D visualisation software, to further assess the land surface in this area. Apart from a thin strip around the coast (around 5-10m), which was too shallow for the vessel to survey, and the tide too high during LiDAR acquisition, we have a true of the surface which includes mobile sand waves, smooth soft sediment, depressions, and rocky areas in the vicinity of the island.

200506 Blogpost 4 PuffinIsland

3D visualisation of merged seamless map of Puffin Island

These images help us refine the hydrodynamics of the area and the impact it has on the historic culture of the island.