ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
An instrument has been developed to make daytime measurements of water vapor in the stratosphere using the technique of photofragment fluorescence. While the use of photofragment fluorescence is by no means unique for measuring water vapor, its application to the stratosphere above 25 km has been limited to two instruments, neither of which are currently operational. In both cases, instrumental contamination was a major concern, especially at the higher altitudes. For this instrument, data are taken during the descent portion of a balloon flight as ambient air is drawn through an aerodynamically designed flow tube. The problem of instrument outgassing is overcome by cryogenically cooling the instrument walls and surfaces that serve as potential sources of water vapor. Additionally, a set of fast response thermistors approximately 8 cm downstream from the optical axis provide the diagnostic capability necessary to identify flow perturbations, which can perturb the measurement. A detailed description is provided of all aspects of the instrument as well as the results of its first two flights. The fluorescence sensitivity of the instrument under zero pressure conditions is about 1.5×10−8 (counts/s)/(molecules/cm3). With a typical solar background of 5000 counts/s and a fluorescence signal of 2500 count/s, a signal-to-noise ratio of approximately 50:1 is achieved for 10 s of averaging throughout the stratosphere. The descent velocity of the instrument through the stratosphere is typically from 3 to 10 m/s, and an altitude resolution of better than 100 m is achieved.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1141198
