INFRARED SPECTRAL RADIANCE MEASUREMENTS IN THE TROPICAL PACIFIC ATMOSPHERE

Downwelling thermal infrared emission from the tropical atmosphere is affected strongly by the typically large amounts of water vapor. In tw o experiments within the last 2 years we have used a Fourier transform spectroradiometer to measure tropical atmospheric emission, concentra ting on the ''window'' region between about 800 and 1200 cm(-1). Short ly after the first of these experiments, substantial differences betwe en measured and calculated radiances led to the development of a new w ater vapor continuum model. This model subsequently has been incorpora ted into several widely distributed radiative transfer codes (LBLRTM, MODTRAN, FASCODE). Measurements from the second tropical experiment, w hich occurred during March and April 1996, validate this new continuum model. This is an important comparison because the new measurements w ere taken with an improved instrument under better defined clear-sky c onditions than the original tropical data on which the continuum corre ction was based. Model residuals are of the order of the uncertainty i n measurements, especially of the atmospheric water vapor and temperat ure profiles.