INFRARED DETERMINATION OF PRECIPITABLE WATER VAPOR IN A VERTICAL COLUMN OF THE EARTH'S ATMOSPHERE

The transmission of the water-vapor absorption bands at 0.96, 1.1 and 1.4 microns is used as the determinant of the total precipitable water vapor in the path of solar radiation. The method was originated by Fowle, and the calibrations established by him are the bases of the present work. Two methods of calibration were employed by Fowle, one using the transmission of the entire area of an absorption band, the other employing the transmission at a single wavelength in the absorption band. The latter method (ordinate method) is much the simpler and yields results of greater consistency than does the area method. The ordinate method of water-vapor determination is less affected by fluctuations in the spectrum envelope created by atmospheric effects than is the area method. Extensive comparison with radiosonde data is made, and a calibration is established for the ordinate method of water-vapor determination in the solar-radiation path by means of the 1.1-µ absorption band. Values of precipitable water vapor for the air above Denver, Colorado, and above Mount Evans, Colorado, are given for certain times of the year.