Balloon-borne measurements of quasi-static electric fields at stratospheric altitudes from low latitudes

Abstract. This paper describes the design, deployment and performance of an improved balloon-borne payload, BEENS-2 (Balloon Experiment on the Electrodynamics of Near Space), developed to measure quasi-static horizontal and vertical electric fields in the low-latitude stratosphere. Measuring weak electric fields (few mV/m) at altitudes up to 32 km presents significant challenges due to ultra-high atmospheric impedance (10¹³–10¹⁴ Ω) and payload-induced interference. We present a differential electrometer design utilizing the INA116 instrumentation amplifier to achieve the necessary input impedance and common-mode rejection. To address limitations identified in previous flights, the BEENS-2 configuration employed non-conducting glass-reinforced plastic booms and a redundant, eight-probe setup. We used an inverted probe setup for the vertical field measurements to distinguish ambient vertical electric field from hardware-induced DC offsets. Experimental results from a flight conducted on January 17, 2025, from Hyderabad, India, reveal that electromagnetic noise from the orienter motor significantly masked ambient signals while the motor was in operation. However, by analyzing data during periods when the motor power was withdrawn and the payload slowed down (rotation with < 2 RPM), we successfully recovered horizontal fields of 15–25 mV/m and a vertical field of ~200 mV/m. The high-resolution data confirms the effectiveness of the measurement approach for future studies on stratospheric electric fields at low latitudes.