IMPROVED IN-SITU TROPOSPHERIC HUMIDITY SENSOR FOR ACCURATE DMSP CALIBRATION

THERE IS A STRONG REQUIREMENT TO OBTAIN IMPROVED UPPER AIR WATER VAPOR DATA. THIS REQUIREMENT ARISES FROM SEVERAL SOURCES AS ENUMERATED IN THE SOLICITATION. THE RADIOSONDE IS THE ONLY PRACTICAL VEHICLE TO OBTAIN THE QUANTITY OF DATA AND VERTICAL RESOLUTION NEEDED. THE RADIOSONDE USES THE CARBON HUMIDITY ELEMENT BECAUSE OF SEVERAL SALIENT FEATURES; IT IS INEXPENSIVE TO MANUFACTURE, VERY REPEATABLE, FAST RESPONDING AT TEMPERATURES ABOVE 0C, AND HAS GOOD SENSITIVITY ABOVE 20% RH. EVEN SO, IT IS UNABLE TO SATISFY THE CURRENT REQUIREMENTS DUE TO SEVERAL UNDESIRABLE CHARACTERISTICS; SPECIFICALLY, IT IS VERY SENSITIVE TO TEMPERATURE DIFFERENCES BETWEEN THE ELEMENT AND THE AMBIENT AIR, IT HAS POOR SENSITIVITY AT LOW RH, AND HAS SLOW RESPONSE BELOW -20C. WE PROPOSE TO USE THE CARBON ELEMENT IN A FORCE BALANCE SYSTEM WHERE THE ELEMENT IS KEPT AT A CONSTANT RH. THIS TECHNIQUE SHOULD ELIMINATE ITS AMBIENT TEMPERATURE SENSITIVITY AND ITS POOR SENSITIVITY AT LOW RH. IT SHOULD ALSO GREATLY IMPROVE ITS LOW TEMPERATURE RESPONSE TIME. WE PROPOSE TO CONDUCT A DEVELOPMENT PROGRAM DESIGNED TO DEMONSTRATE THE OPERATIONAL SUITABILITY OF THE TECHNIQUE AND PERFORM INITIAL LABORATORY TESTS TO DEFINE ITS PERFORMANCE CHARACTERISTICS