A new type of untethered balloon based mapping platform allows affordable remote sensing applications from higher altitudes and with a greater range and payload capacity than common motorized UAV’s. The airborne device, called « Stratochip » is based on a dual helium balloons configuration. At a defined altitude (comprised between 500 and 30000m), the first balloon is released, drastically reducing the platform climbing rate. The payload (up to 10kg) can then drift in a sub-horizontal trajectory until it leaves a pre-defined area of interest. Leaving the pre-defined area, the second balloon is released and the payload is recovered after a parachute landing. The predicted flight path of the Stratochip, launch site and surveyed area are calculated using both forecasted (NOAA model) and real-time (inborne instruments) meteorological data, along with the physical parameters of the balloons and parachute. The predicted recovery area can also be refined in real-time to secure and facilitate equipment retrieval. In this study, we present the results of two cartographic campaigns made in Belgium (Ground collapse near Mons) and Spain (karstic field in the Eastern part of Sierra Arana, Granada region). Those campaigns aimed to test the usability of the Stratochip to survey a large area (up to 900km² for Spain) at medium and low altitudes (8000m - 500m) and produce an updated Digital Elevation Model and orthophoto mosaic of those regions. For that purpose, the instrument installed in the Stratochip payload was constituted of a digital camera stabilized with two IMU’s and two brushless motors. An automated routine then tilted the camera at predefined angles while taking pictures of the ground. This technique allowed to maximize the photogrammetric information collected on a single pass flight, and improved the DEM reconstruction quality, using structure-from-motion algorithms. The quality of produced DEM were then evaluated by comparing the level and accuracy of details and surface artefacts between available topographic data (LIDAR, SRTM, topographic maps) and the Stratochip sets. This evaluation showed that the models were in good correlation with existing data, and can be readily be used in geomorphology, structural and natural hazard studies.

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