where the emission of the excited [[spi:math]] in the measured UV spectral range of (2500-5000) [[spi:math]] have a cross-section [[spi:math]] for 900 eV Ar+ impact. In addition, the emission cross-section for the 3914 [[spi:math]] line of (43) is [[spi:math]] [Thomas, 1972]. These measurements allow us to make a sample assessment of the factors controlling possible interference with optical earth sensors. Consider the impact of Ar+ (density NA, speed [[spi:math]]) upon atmospheric nitrogen of density N and scale height H with excitation cross-section [[spi:math]]. The emission intensity I from a 1-cm2 column is given by where the quantities in the numerator of the right hand side are expressed in cgs units. Thus the emission intensity depends entirely on the density dis36 A second mechanism of airglow modification is much more serious since it affects directly the UV portions of the spectrum where some critical sensors operate. This is due to direct impact upon the atmosphere by 3.5 keV Ar+ beam from the vicinity of LEO. We call this process "artificial aurora" because it is a direct analog except that the excitation agent is 3.5 keV Ar+ instead of (1-10) keV electrons from the aurora. Unlike the case of auroral excitation, excitation cross-sections for Ar+ collisions with atmospheric atoms and molecules are not as well-measured as with energetic electrons. The only applicable measurement is reported by Liu and Broida (1970) for the excitation reaction [[spi:math]] (43) [[spi:math]] (44)
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