INTEGRATION OF A SMALL UNPILOTED AIRBORNE SYSTEM, PHOTOGRAMMETRY, AND FIELDMOVE FOR METER-SCALE STRUCTURAL AND FACIES MAPPING OF THE SURFACES OF OBSIDIAN LAVAS

The upper surfaces of Holocene silicic lavas are possibly the roughest naturally occurring landscapes on Earth with meter- to decameter-scale ridges and troughs interspersed with crevasses and isolated pinnacles. Airborne lidar digital terrain models capture some of this roughness and complexity but have insufficient resolution to make usable topographic basemaps for analysis of sub-decameter-scale structures. In order to collect structural measurements at useful outcrop scales in FieldMOVE, we developed a work-flow with a DJI Phantom 4 Advanced small unpiloted aerial system (sUAS) and Structure-from-Motion photogrammetry to generate <10 cm-scale resolution color orthorectified airphotos. Over a ~36 hour period, we would (1) plan aerial photography missions in DroneDeploy or Map Pilot in the evening, (2) fly the missions the following morning when wind speeds are low and there are few or no clouds, (3) map onto the previous day's airphoto in FieldMOVE, and (4) recharge the batteries, generate the day's Structure-from-Motion model and orthorectified airphoto in Agisoft Metashape Pro, and plan the next day's flights. We used a small gasoline-powered generator to charge batteries and iPads, and power the laptop while camping off-grid at Medicine Lake and Newberry calderas. This workflow was remarkably simple and effective, and allowed us to navigate on the lava by visible features including specific blocks and boulders. This also allowed us to manually correct the already excellent GPS location from the iPad and FieldMOVE. The quality of the ~3 - 5 cm-resolution orthorectified airphotos allowed individual structural measurements to be placed manually and exactly, for example, at the intersection of two, 2 cm-wide fractures, or around the hinge of a meter-scale isoclinal fold. FieldMOVE and FieldMOVE Clino were used for data collection with great success and no data was lost due to software failures or corruption. The ability to readily switch between basemaps and the wide choice of structural symbols made mapping efficient such that up three mappers could collate their data at the end of the day and have a complete map and associated stereonets. We look forward to using StraboSpot and StraboTools as complimentary field apps. In summary, this study would have been impossible without the availability of FieldMOVE, the ability to complete computationally intensive photogrammetry on a field laptop, and access to an easy to fly, affordable sUAS, and most importantly the ability to integrate these technologies quickly and smoothly.