Project Title:

A Diode Laser Airborne Hygrometer

Southwest Sciences, Inc.
1570 Pacheco St., Suite E-ll
Santa Fe, NM 87501

93-1-08     06   1322

A Diode Laser Airborne Hygrometer

Abstract:

Southwest Sciences proposes the development of a
diode-laser-based hygrometer for atmospheric studies. The
instrument dynamic range will span dew (frost) points of +40ø C
down to -90ø C and will be suitable for in situ measurements
throughout the troposphere and tropopause. Response times will be
1 second, or less. The planned instrument detects absolute water
vapor concentrations using optical spectroscopy with a
custom-fabricated InGaAsP diode laser operating at 1393 nm.
Optical absorbance measurements are made using high frequency
wavelength modulation spectroscopy (WMS) which, we anticipate,
will be capable of minimum detectable absorbances of 1 x 10-5
providing a signal-to-noise ratio of 3 for the lowest water
concentrations. Fiber optics will "pipe" the light from the laser
to the measurement point thereby eliminating unwanted absorbance
due to water vapor outside of the actual measurement path. The
Phase I experiments are expected to demonstrate the feasibility
of the diode-laser-based system for detecting water vapor
accurately and rapidly over a nearly million-fold range of
concentrations. The Phase II program will culminate in the
delivery of a fully-automated hygrometer for airborne studies.

Reliable, inexpensive airborne humidity sensors have commercial 
potential for aircraft icing indicators and local weather
forecasting. Our trace gas detection methods also can be adapted
to a wide variety of other gases. Applications include continuous
monitoring of chemical processes, open path monitoring of toxics,
and on-line purity determination of process gases.

diode laser, water vapor, hygrometer