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Approved for public release; distribution unlimited. C-- LUJ LL.AIR ii boo;=*m V 0. Abstv'act continued computes infrared radiances for an earth's limb viewing geometry. The nominal spectral region of this study lies between 2.7 and 25 -,irometers and emphasis is placed on radiation originating at alt.tudes between 70 and 500 kin. The physical model is described, with emphasis on the changes required in extending its usefulness, Application of the computer program is described. Model predictions are comp,-(.d with radiance data obtained in the ICECAP auro-al studies program.i'nis comparison is used to illustrate uncertainties in results due to ds't-mptions made in the model and lack of data on actual atmospheric cr,ý)iposition., INTRODUCTIONThe research reported here has had as its major objective the development and improvement of infrared radiance and transmission models of the atmosphere. These models are designed to simulate the radiative properties of the atmosphere to provide predictions for Air Force and other Department of Defense design and surveillance programs. Comparison with available exoerimental measurements provides greater understanding ot the atmosphere and serves to check the adequacy of the models.The main areas of effort have been 1. Extension of the applicability of a current model on non-equilibrium atmospheric infrared radiance between 2.5 and 25 microns.2. Development and improvement of thermal equilibrium models of the infrared transmission and radiance for the earth's lower atmosphere.The goal of the first area has been the further development of a computer program to simulate the natural infrared radiance background of the earth's upper atmosphere. The nominal spectral region under study lie" between 2.7 and 25 micrometerJ a4nd emphasis is placed on radiation originatinq at altitudes between 7t) and 500 kilometers, The general problem area is of interest for systems design, military surveillance and the advancement of knowledge about physical processes in the upper atmosphcre. The immediate application of this work is to aid in developin9 optimum infrared background measurements programs and in interpreting the results of su,.h measurements..This work is an extension of the study of Corbin, et al (1969) and Degges (1972Degges ( , 1974. The fomner investigated the natural infrared backqround of the earth in 5 to 25 micrometer' spectral reqion, with the goal of estimating earth 1imb viewingi radiances for tangent heights from the surface to 500 kti altitude. For convenience, their study divided the atmosphere into two regions with a division at 70 km. Below 70 km the atmosphere was assumed to be in thermal equilibrium. Above 70 km explicit calculations were made of processes which excite and de-excite mullectia vibrational and rotational levels which are the sou.-ce )f infrared radiation, Their study concentrated on radiation from water vapor, carbon dioxide, ozone, nitric oxide and nitrous oxide, which are principal radiating species in the spectral region considered. In addition, ni...

Vibrational levels of the ground states ((2)pi (1/2), 3/2) of nitric oxide are populated by transfer of vibrational quanta in collisions with molecular oxygen and nitrogen; by atom exchange with atomic oxygen; by absorption of infrared radiation from the earth's surface, the lower atmosphere, and the sun; by fluorescent decay of the beta-, gamma-, and delta-band systems following resonance absorption of solar ultraviolet radiation; by electron impact excitation; and during chemical formation. These excitation mechanisms are balanced by collisional deexcitation and by radiation in the infrared vibration rotation bands. The relative importance of each of these processes is assessed for quiescent day and night conditions and for aurorae. In the absence of collisional interactions, absorption of terrestrial infrared radiation maintains a vibrational temperature of between 220 K and 270 K near the mesopause.