Project Title:

High Sensitivity Water Vapor Measurements from Phase Determination

94-1	08.05	2820

High Sensitivity Water Vapor Measurements from Phase Determination

Abstract:

This proposal is submitted in response to NASA SBIR Subtopic 8.05 
which solicits proposals for micro-instrumentation to measure water 
vapor from airborne platforms. An innovative technique for 
determining water vapor concentrations that is over 100 times more 
sensitive than conventional diode laser absorption spectroscopy for 
the same laser power, path length, and absorption line strength is 
presented. This technique is will result in a low cost and very 
compact instrument able to 
measure routinely in situ water vapor concentrations from well 
below frost point temperatures of -90@C (2.5 x 1012 
molecules/cm3) to well above +15@C (4 x 1017 molecules/cm3). The 
technique can be easily applied to other trace gas constituents 
and can be constructed entirely from mass produced low cost 
components making it especially viable for commercial 
production. The proposed instrument utilizes an inexpensive, 
room temperature tunable laser diode as a stable, single-
frequency, high-output light source. The instrument is designed 
to be lightweight, extremely compact, rugged, and to have low 
power requirements. The proposed measurement technique is 
insensitive to hostile environments and can be 
operated during the day or at night. 

The simplicity, size, low cost, and sensitivity of the 
instrument make it ideal for unattended measurements either 
for space or ground-based applications. The technique could 
easily be expanded to include other trace gases or pollutants. 
Commercial applications would include: radiosonde 
measurements, atmospheric monitoring by commercial aircraft, 
vacuum chamber residual gas monitors, air quality monitors 
sensitive to selected trace constituents, chemical process 
monitors, stack gas monitors, baseline monitoring for 
utilities, and chemical instrumentation for treaty 
verification. 

KEY WORDS

Visidyne, Inc.
10 Corporate Place
South Bedford Street
Burlington, MA  01803