EAGER: Fiber-Optic Temperature Profiler for Long Duration Ballooning - Proof of Concept

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This is a project to develop a new technology for temperature profiling from super-pressure balloons that fly along constant density surfaces, typically in the stratosphere. The sensor is a fiber-optic temperature profiler (FTP), consisting of a 2-4km length of optical fiber suspended from the gondola of a balloon. Temperature is determined along the length of the fiber from the backscatter returned from a laser pulse injected at the top of the fiber. Changes in the temperature of the fiber lead to changes in Raman scattering (particularly the wavelengths of the stokes and anti-stokes lines), which can be inverted to retrieve temperature, and the timing of the laser pulses can be used to ascribe the temperature measurement to a specific linear position along the fiber. This technology is currently used for industrial applications (e.g. borehole temperature sensing in oil and gas drilling operations), and the sensors are commercially available. However, it requires substantial enhancement before it can be deployed from a balloon gondola. In addition to the core instrument, several other components must be developed to form a complete system. One of these is an end-of-fiber module which is weighted to make the fiber hang more or less vertically and contains a thermometer and a GPS receiver. The GPS receiver determines the position of the bottom end of the fiber, which is combined with a position fix from a GPS receiver in the gondola to estimate the altitudes of the temperature readings. Additional components include a data and control system and a fiber deployment system, the latter consisting of a spool that reels out the fiber once the balloon reaches altitude. Funds provided here will be used to develop a prototype and conduct a test flight. The work has scientific broader impacts due to the wide variety of potential applications of the system. The primary intended use of the system is for sounding the Tropical Tropopause Layer (TTL). There is considerable interest in the fine-scale temperature structure of the TTL, particularly as it relates to issues including the difference between cloud-top height and the height of the cold-point tropical tropopause, the minimum temperature of the TTL and its role in limiting the transport of water vapor into the stratosphere, and the temperature perturbations associated with vertically propagating gravity waves.