Stratospheric balloon campaigns with AIRDOS-class detectors

AIRDOS detectors have been the primary scientific payload in a series of FIK stratospheric balloon flights operated jointly with the Nuclear Physics Institute of the Czech Academy of Sciences. The flights serve a dual purpose:

  1. Atmospheric radiation mapping — establishing the altitude dependence of secondary cosmic radiation up to ~30 km and the location of the Regener–Pfotzer maximum.
  2. Instrument qualification — testing AIRDOS and other detector designs against the temperature, pressure, mechanical, and electromagnetic environment of a stratospheric flight before they are deployed on a longer mission (UAV, satellite).

Multi-detector payload

A typical FIK-6 payload combined three different radiation detectors so that they could be cross-calibrated against the same air column on a single ascent:

  • SPACEDOS — silicon PIN diode sensor, low mass, low power, very high resistance to mixed-field events.
  • AIRDOS-C — scintillation detector with a small NaI(Tl) crystal coupled to a SiPM.
  • G-M tube (STS-5) — high-volume Geiger–Müller counter for total-flux reference.

All three detectors plus the supporting sensors (T/p/RH, IMU, GNSS) were carried inside a polystyrene gondola flown by a Hwoyee Weather Balloon 1600 in the FIK-6 configuration:

FIK-6 experiment setup

The TF-ATMON-based avionics recorded the full sensor suite throughout each flight. An example of the raw data — temperatures, pressure, humidity, three detector count rates, and altitude — from FIK-6:

FIK-6 raw flight data

Why telemetry data matters

The combined flight + radiation record shows several effects that would have been misinterpreted without simultaneous mechanical telemetry. The acceleration and angular-rate trace from the IMU reveals that the silicon PIN diode count rate spikes at takeoff, balloon burst, and landing — a microphonic effect of the detector electronics, not a real radiation increase. The increased noise during the descent is similarly associated with rotation and high angular rates of the gondola:

FIK-6 acceleration and angular speed

The TF-ATMON architecture, with balloon-specific avionics decoupled from the detector payload, makes this kind of cross-correlation routine — every payload publishes its data to the same logger, sharing time, position and environmental context.

Regener–Pfotzer maximum

A central result of the FIK campaign is the joint determination of the altitude of the Regener–Pfotzer maximum from all three detector types on the same air column. A log-normal fit to the measured count rate vs. altitude gives a maximum near 19 km for all three detectors (G-M tube, NaI(Tl) scintillator, and silicon PIN diode):

Regener–Pfotzer maximum from FIK-6

The methodology, including the use of TF-ATMON and the comparison across detector types, is reported in: J. Kákona et al., Measurement of the Regener–Pfotzer maximum using different types of ionising radiation detectors and a new telemetry system TF-ATMON, Radiat. Prot. Dosim. 198(9–11): 712–719, 2022, and extended to latitudinal effects in Ambrožová et al., 2023.

Recovery and operational notes

The TF-ATMON telemetry also makes balloon recovery practical: position and trajectory prediction were precise enough during the FIK-6 flight that the rescue team could observe the gondola touchdown directly and recover it within minutes:

FIK-6 recovery via HabHub tracker

The main open challenge is launching balloons under the strong wind conditions that typically precede thunderstorm activity — these are exactly the conditions of scientific interest, but they are also when the gondola is most likely to impact terrain or the launching operator:

Stratospheric balloon takeoff under high wind

This is one of the reasons for the parallel development of the TF-G2 autogyro UAV platform — a controllable carrier that can position the same detectors in or near a storm cell with much higher reliability than an uncontrolled balloon. The latest AIRDOS03 variant was designed specifically for that UAV use.