Integration of a Vector Electric-field Sonde into a Small UAS

For lightning research a UAS could can provide an airborne platform to collect data related to the particle charge problem, and could provide a rapid deployment function to measure vector electric fields caused by lightning flashes near hurricanes and tornados. We report on the first integration of a vector electric field sonde (an ESonde) into a UAS. The integration required a significant weight and size reduction of the original Esonde developed for balloon deployment. Substantial weight and size benefit was achieved by sharing the batteries of the Tempest UAS with the Esonde. The UAS also shares its orientation information (obtained with an onboard magnetometer) with the Esonde. Synchronization between the UAS and the Esonde is done by accurate time stamping of both systems using on-board GPS time references. Finally, the UAS provides a means to safely return the Esonde after the experiment. In balloon applications, a sonde must include telemetry to report its position and allow recovery. A custom data acquisition system that streams 16-bit data at 500 kSamples/second to onboard SD cards was created. Four channels of electric field are measured by electrodes on a streamlined probe that is mounted atop the Tempest UAS airframe. From the four measurements, the three components of electric field can be derived. Substantial modeling with COMSOL was performed in order to properly place the electrodes and estimate the disturbance of the local electric field caused by the airframe. The entire system is 2.5-inches in diameter, 19.5-inches long and weighs 2 pounds. When this electric field measurement is combined with lightning-mapping array data to give channel locations, a complete description of charges and currents in an intra-cloud flash can be derived. This system could be immediately useful in Oklahoma, Colorado and Alabama; all locations with permanent lightning mapping arrays.