A DIODE LASER HUMIDITY SENSOR FOR COLD ENVIRONMENTS

MEASUREMENTS OF ATMOSPHERIC HUMIDITY IN COLD REGIONS OR WINTER FIELD ENVIRONMENTS ARE DIFFICULT USING EXISTING METEOROLOGICAL INSTRUMENTATION. IN GENERAL, PRESENT FIELD INSTRUMENTS FOR UNTENDED HUMIDITY MEASUREMENTS ARE PLAGUED BY LOW SENSITIVITY AND DRIFTS IN CALIBRATION, RESULTING IN POOR ACCURACY AND LOW RELIABILITY. WE PROPOSE A NEW INSTRUMENTATION CONCEPT FOR FIELD MEASUREMENT OF HUMIDITY, BASED ON ABSORPTION OF NEAR-INFRARED RADIATION FROM LOW-COST, COMMERCIAL INGAAS LASER DIODES. ADVANTAGES OF THE LASER DIODE HYGROMETER INCLUDE HIGH SENSITIVITY ACROSS THE FULL RANGE OF EXPECTED TEMPERATURES,FAST TIME RESPONSE, NO DEGRADATION OF PERFORMANCE NEAR SATURATION, AND SIMPLE CALIBRATION. THE UNDERLYING CONCEPTS OF THIS APPROACH WILL BE TESTED IN PHASE I USING LABORATORY BREADBOARD INSTRUMENTATION. THESE TESTS WILL EMPHASIZE EVALUATIONS OF SENSITIVITY, ACCURACY, AND CALIBRATION STABILITY, INCLUDING MEASUREMENTS OF HUMIDITY UNDER CONDITIONS SIMULATING WINTER FIELD ENVIRONMENTS. WE BELIEVE THAT COMPACT AND RELIABLE INSTRUMENTATION BASED ON THIS CONCEPT CAN BE DEVELOPED FOR UNTENDED FIELD OPERATION IN COLD ENVIRONMENTS AS WELL AS A WIDE RANGE OF OTHER APPLICATIONS WHERE SENSITIVE HUMIDITY MONITORS ARE REQUIRED.