Determination of CO2 mixing ratio columns from space using Laser Absorption Spectroscopy (LAS) requires simultaneous measurements of CO2 number density columns and knowledge of the dry atmospheric surface pressure. One approach to determining the surface pressure is to make an LAS column measurement of O-2 number density in the 7857.3-7921.7 cm(-1) (1.27 mu m) region of the O-2((1)Delta) state. A complicating factor in the LAS O-2 measurement is the presence of a permanent but spatially variable natural source of airglow from the O-2((1)Delta) state. In addition, the laser radiation can induce stimulated emission from the ambient O-2((1)Delta) state and also cause stimulated absorption and emission from the ground state O-2 molecules as the laser beam passes through the atmosphere. Finally, the upwelling surface-reflected solar radiation is an additional source of background radiation. The effects of these additional radiation sources on the LAS measurement of O-2 are examined. The surface-reflected solar radiation produces the largest background at 3 orders of magnitude more intense than the laser backscatter signal, while the airglow is of the same order of magnitude as the laser backscatter. The stimulated emission from ambient O-2(a(1)Delta(g)) is found to be about the same order of magnitude as the laser radiation. These effects are evaluated under noon, twilight, and midnight conditions at midlatitudes, the equator, and the pole. The stimulated emission is in the same direction and in phase with the laser signal, its contamination of the LAS O-2 measurement prevents a full sunlight determination of surface pressure.

We report standoff open path atmospheric CO2 monitoring with a field deployable, turn key system including a continuous wave (CW) distributed feedback (DFB) laser and an erbium. doped fiber amplifier (EDFA) at 1.5-mum. A sensitivity of 28-ppm was achieved over 1.5-km of open air with 200-pW of received power, a 10s acquisition time. and a peak absorption cross section of 8x10(-23). This sensitivity corresponds to an error in fractional absorbance of 8x10(-3). Closed cell lab sensitivities are better than 3000ppm*m, an error in fractional absorbance of 5x10(-4). These results have been achieved using space qualified laser components, un-cooled InGaAs detectors, and off the shelf electronics in a rugged all fiber architecture.

This paper describes a technique for the retrieval of altitude profiles of the atomic oxygen concentration (n = [O]) and temperature (T) from ground‐based measurements of the O+(²D ‐ ²P) doublet at 7320 and 7330 Å in the twilight airglow. The technique is based on previously demonstrated knowledge that at solar zenith angles (SZA) characteristic of twilight conditions, the upper state of the 7320‐Å doublet transition is produced by photoionization and photoelectron impact ionization of atomic oxygen and lost mainly by radiative decay, thereby providing a sensitive dependence on [O]. We apply inverse problem theory to retrieve the exospheric temperature (T∞), the atomic oxygen concentration at 120 km (n120), the temperature at 120 km (T120) and the temperature profile shape factor (S) using a Bates‐Walker representation of n given approximately by n = (n120T120/T) exp[−z] where T = T∞ ‐ (T∞ ‐ T120)exp[−S(h ‐ h120)], z is the reduced height, and h is the altitude. The algorithm is tested and theoretically verified using synthetic data sets where random errors of measurements are characterized by Poisson noise due primarily to sky background. In the tests that we report here the solar EUV flux is specified. In a separate paper we will report how the solar EUV ionization rate can be independently derived from various twilight emissions. By comparing retrieved with known input values, it is demonstrated that for the altitude range 200 to 500 km the atomic oxygen concentration [O] can be retrieved with relative errors ≃15% and systematic errors of about 25% if the solar EUV is given. Sensitivity of the results to noise, sample size (degrees of freedom), and absolute calibration are quantitatively evaluated. In addition, to demonstrate the validity of the technique experimentally, we utilized the Atmosphere Explorer E (AE‐E) in situ measurements of the solar EUV flux and [O], with the latter taken when perigee was over Arecibo on an occasion when the observatory airglow spectrometer was simultaneously measuring the 7320‐Å emission from the ground during twilight. The results show excellent agreement with the measured [O] values which were ∼ 50% lower than the mass spectrometer incoherent scatter (MSIS‐86) model values at ∼ 300 km on that day, thereby demonstrating the value of the method for monitoring day‐to‐day variations in [O] and the temperature.

In this paper we demonstrate that it is possible to invert twilight observations of the O+(²D ‐²P)‐7320 Å airglow emission to obtain information about both the thermospheric atomic oxygen densities and the unattenuated O+(²P) ionization frequency. The efficacy of the proposed approach, which relies upon making twilight observations in more than one viewing direction, is illustrated using a synthetic data set and an inversion algorithm based on a simple photochemical model. The results of this study show that day‐to‐day variations in the thermospheric oxygen atom densities may be monitored from the ground without requiring complementary measurements of the solar EUV flux. The study also shows that twilight observations may be used to monitor variations in the solar flux components that are responsible for O+(²P) production and EUV heating of the upper thermosphere.

The Thermal Ion Dynamics Experiment (TIDE) combines differential measurements of angle, energy, and mass to determine the detailed distribution function of low energy magnetospheric ions in the range of 0 to 100 eV. Goals included designing a 1 sq cm entrance aperture, minimizing trajectory divergence at exist aperture, and minimizing internal scattering. Design parameters were used to construct the test model.

Data from the visible airglow experiment on the Atmosphere Explorer‐E satellite have been used to determine the quantum yield of O(¹S) and O(¹D) from the dissociative recombination of O 2 + . A range of values between 0.09 and 0.23 has been obtained for the quantum yield of O(¹S). It is shown that the quantum yield of O(¹S) depends on the ratio of electron density to atomic oxygen density. This suggests that the quantum yield of O(¹S) may depend on the degree of vibrational excitation of the recombining O 2 + . The quantum yield of O(¹D) has been measured to be 1.23±0.42, with no dependence on the electron‐oxygen ratio.

A method is described to determine the concentration of atomic oxygen in the altitude range 100 to 160 km in an aurora from the ratio of the volume emission rates of the O(¹S) 5577Å to N2+ in 3914Å emissions. Applying the technique to previously published measurements it is found that the O density at 100 km is typically about 1 × 1011cm−3. The occurrence of densities in excess of 2 × 1011cm−3 in the aurora at 100 km is rare.

Analysis of the O I (λ5577 A) airglow observations conducted on board the Atmosphere Explorer C satellite yields the following results when combined with simultaneous measurements of ion and neutral composition. A volume emission rate profile derived after sunset requires the production of an O(¹S) atom in 8% of the O2+ recombinations. Photoelectron impact on atomic oxygen and the dissociative recombination of O2+ are important sources of O(¹S) in the dayglow; however, the airglow measurements require a large additional production of O(¹S) below 200 km in addition to these. The reaction N + O2+ → NO+ + O(¹S) can provide the missing O(¹S) source if the rate coefficient is near 2.5 × 10−11 cm³ s−1.

Results are presented for an experimental study designed to measure the density of H2 near 100 km in the earth's atmosphere from occultation of a star, Gamma Vel, by the earth's atmosphere at several wavelengths near the H2 absorption line at 1108.128 A by a spectrometer on an orbiting astronomical observatory. Measurement of the O2 density between 95 and 123 km is also reported. Attention is focused on testing the predictions of a model of the distribution of hydrogen constituents, H, H2, H2O, CH4, OH, and H2O in the upper atmosphere related to a theory of hydrogen escape developed by Hunten and Strobel (1974) and by Liu and Donahue (1974). The measured H2 densities are found to be in good agreement with recent theoretical predictions, whereas the measured O2 density profile generally agrees with the models except for a wavelike structure in the range 104-114 km.

Analysis of the O I /5577-A wavelength/ airglow observations conducted on board the Atmosphere Explorer C satellite yields the following results when combined with simultaneous measurements of ion and neutral composition. A volume emission rate profile derived after sunset requires the production of an O(1S) atom in 8% of the O2(+) recombinations. Photoelectric impact on atomic oxygen and the dissociative recombination of O2(+) are important sources of O(1S) in the dayglow; however, the airglow measurements require a large additional production of O(1S) below 200 km in addition to these. The reaction N + O2(+) yielding NO(+) + O(1S) can provide the missing O(1S) source if the rate coefficient is near 2.5 times 10 to the minus 11th cu cm per sec.

A payload consisting of a number of experiments to study the earth's atmosphere was launched from White Sands on Feb. 8, 1971. The differential photoelectron flux spectrum was measured as a function of altitude. The energy distribution revealed the N2 vibrational structure appearing at 2.8 V, rising to a maximum at 4 eV, decreasing to an 8-volt-wide plateau at 20 V, and then further decreasing. The ion and electron density distributions were measured simultaneously. An optical measurement of forbidden O I 5577-A radiation was made. Both electron impact on atomic oxygen and dissociative recombination of O2(+) were found to produce this emission above 150 km. The recombination rate for the O(1 S) found from a reported nightglow profile is 2.5 plus or minus 1.5 x 10 to the minus 9th cu cm/sec. Between 140 and 120 km, photodissociation is a source of 5577 radiation. Chapman three-body recombination is dominant below 120 km.