| Instrument: | Balloon Borne Frost-Point Hygrometer |
| Principal Investigators: | Samuel J. Oltmans |
| Co-Investigators: | Holger Vömel |
| Collaborator: | David J. Hofmann |
| Organization: | National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory Mail Code: RE/CG1 325 Broadway Boulder, CO 80303 |
Measurement Description: The instrument is based on a chilled mirror principle and measures the temperature of a mirror which is controlled such that the mirror maintains a small and constant layer of frost coverage. Under these conditions the mirror temperature equals the frost point temperature of the air passing over the mirror. The frost coverage on the mirror is detected by a phototransistor which senses the light of a light-emitting diode reflected off the mirror surface. This signal is compared to a reference signal, thus eliminating the temperature drift of the elements. The error signal is then used to control the temperature of the mirror. The mirror temperature is measured using an individually calibrated bead thermistor. The mirror temperature is transmitted to the ground station using a Vaisala radiosonde, which also provides ambient temperature and pressure, and in the lower and middle troposphere relative humidity.
| Platform: | Usually small rubber or plastic balloons |
| Accuracy: | 10-15% |
| Response Time: | Depends on altitude, typically 15 sec |
| Size: | 30 x 40 x 30 cm |
| Weight: | 6 kg |
Reference:
Oltmans, S. J., Measurements of water vapor in the stratosphere with a frost point hygrometer, Measurement and Control in Science and Industry, Proceedings of the 1985 International Symposium on Moisture and Humidity, Washington, D. C., pp. 251-258, Instrument Society of America, 1985.
Oltmans, S. J., and D. J. Hofmann, Increase in lower-stratospheric water vapour at a midlatitude Northern Hemisphere site from 1981 to 1994, Nature, 374, 146-149, 1995.
Vömel, H., S. J. Oltmans, D. J. Hofmann, T. Deshler, and J. M. Rosen, The evolution of the dehydration in the Antarctic stratospheric vortex, J. Geophys. Res., 100, 13919-13926, 1995.
Vömel, H., S. J. Oltmans, D. Kley, and P. J. Crutzen, New evidence for the stratospheric dehydration mechanism in the equatorial Pacific, Geophys. Res. Lett., 22, 3235-3238, 1995.