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 1000 and 30000m), a GPS based controller automatically releases the first balloon, drastically reducing the ascent rate. The payload (up to 10kg) can then float in a sub-horizontal trajectory until it leaves a pre-defined area of interest. At this point, 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 physical parameters of balloons and parachute, as well as sounding meteorological data (NOAA windgram model) and real-time flight rates, along with the. The predicted recovery area can also be refined in real-time to secure and facilitate equipment retrieval. The Stratochip was tested to survey large areas at medium altitudes (1500m-8000m) in mountainous areas (Sierra Nevada, Spain) and hilly landscapes (Belgium). In a few flights, the platform allowed to produce several hundred squares kilometers of Digital Elevation Models and orthophoto mosaics. 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. Recontructed DEM’s and orthophoto’s have been referenced using ground control points from satellite imagery (Spain, Belgium) and DPGS (Belgium). The quality of produced DEM were then evaluated by comparing the level and accuracy of details and surface artifacts with available topographic data. This evaluation showed good correlation with existing data, improved the detail level in some areas and can be readily be used in Geomorphology, Structural Geology and Natural Hazards studies.
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