22 Apr 2022
22 Apr 2022
Status: this preprint is currently under review for the journal AMT.

A Fiber Optic Distributed Temperature Sensor for Continuous in situ Profiling 2 km Beneath Constant-altitude Scientific Balloons

J. Douglas Goetz1, Lars K. Kalnajs1, Terry Deshler1, Sean Davis2, Martina Bramberger3, and M. Joan Alexander3 J. Douglas Goetz et al.
  • 1Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, CO, USA
  • 2NOAA Chemical Sciences Laboratory, Boulder, CO, USA
  • 3NorthWest Research Associates, CoRA Office, Boulder, Colorado, USA

Abstract. A novel fiber optic distributed temperature sensing instrument named the Fiber-optic Laser Operated Atmospheric Temperature Sensor, or FLOATS, was developed for continuous in situ profiling of the atmosphere up to 2 km below constant altitude scientific balloons. The temperature sensing system uses a suspended fiber optic cable and temperature dependent scattering of pulsed laser light in the Raman regime to retrieve continuous 3 m vertical resolution profiles at a minimum sampling period of 20 s. FLOATS was designed for operation aboard drifting superpressure balloons in the tropical tropopause layer at altitudes around 18 km as part of the Stratéole 2 campaign. A short test flight of the system was conducted from Laramie, Wyoming, in January 2021 to check the optical, electrical, and mechanical systems at altitude and to validate a four-reference temperature calibration procedure with a fiber optic deployment length of 1170 m. During the 4-hour flight aboard a vented balloon, FLOATS retrieved temperature profiles during ascent and while at a constant float altitude of about 19 km. The FLOATS retrievals provided differences of less than 1.0 °C compared to a commercial radiosonde aboard the flight payload during ascent. At float altitude, a comparison of optical length and GPS position at the bottom of the fiber optic revealed little to no curvature in the fiber optic cable suggesting that the position of any distributed temperature measurement can be effectively modeled. Comparisons of the distributed temperature retrievals to the reference temperature sensors show strong agreement with root mean square error values less than 0.4 °C. The instrument also demonstrated good agreement with nearby meteorological observations and COSMIC-2 satellite profiles. Observations of temperature and wind perturbations compared to the nearby radiosounding profiles provide evidence of inertial gravity wave activity during the test flight. Spectral analysis of the observed temperature perturbations shows that FLOATS is an effective and pioneering tool for the investigation of small scale gravity waves in the lower stratosphere.

J. Douglas Goetz et al.

Status: open (extended)

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  • RC1: 'Comment on amt-2022-93', Anonymous Referee #1, 19 Aug 2022 reply

J. Douglas Goetz et al.

J. Douglas Goetz et al.


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Short summary
An instrument for in situ continuous 2 km vertical profiles of temperature below high altitude balloons was developed for high temporal resolution measurements within the upper troposphere and lower stratosphere using fiber optic distributed temperature sensing. The mechanical, electrical, and temperature calibration systems were validated from a short midlatitude constant altitude balloon flight within the lower stratosphere. The instrument observed small-scale and inertial gravity waves.