NATIONAL SPACE SCIENCE DATA CENTER DOCUMENTATION THE VISIBLE AIRGLOW EXPERIMENT ON ATMOSPHERE EXPLORER-C, -D, and -E Principal Investigator Dr. Paul B. Hays Space Physics Research Laboratory The University of Michigan Department of Atmospheric ant Oceanic Science Ann Arbor, Michigan 48109 June 1977 I. VAE Capability and Sensitivity The Visible Airglow Experiment (VAE) on Atmosphere Explorers C, -D and -E (AE-C, -D, -E) is an airglow photometer designed to measure various thermospherlc emission features during the day and night both at low latitudes and in auroras. The photometer has two distinct optical channels, a high sensitlvity channel (channel 2) with a large field of view (3 degrees half angle cone) and a low sensitivity channel (channel 1) with a narrow field of view (3/4 degree half angle cone) to resolve small airglow features. The system is protected by a combination 100 to 1 attenuating system and a cathod back biasing scheme which allows measurements of maximum sensitivity within a fraction of a second of viewing the bright limb of the earth. The experimental design allows six atmospheric emissions from the near ultraviolet to the near infrared to be monitored regularly on each satellite. The six filters are mounted on a wheel along with a dark position and calibrate position. The calibration source is made of phospher and is activated by radioactive promethium. Each optical system employs a combination of a simple objective lens and field stop to define the angular field of view. The integration periods for channels 1 and 2 are 32 and 120 msec, respectively. A summary of the emission wavelengths and their atmospheric sources measured on each satellite follows: VAE-C 1. OI (3P - 1D) emission at 6300A 2. OI (1D - 1S) emission at 5577A 3. OII (2D - 2P) emission at 7319-30A 4 NI (4S - 2D) emission at 5200A 5. N2I (B3 PIg, v=0 - C3 PIu, v=0) emission band at 3371A 6. N2II(X2 SIGMAg+, v=1 - B2 SIGMAu+, v=0) emission band at 4278A VAE-D 1. OI (3P - 1D) emission at 6300A 2. OI (1D - 1S) emission at 5577A 3. OII (2D - 2P) emission at 7319-30A 4 NI (4S - 2D) emission at 5200A 5. N2II(X2 SIGMAg+, v=1 - B2 SIGMAu+, v=0 ) emission band at 4278 6. HI (n=2-4) emission 4861A VAE-E 1. OI (3P-1D) emission at 6300A 2. OI (1D-1S) emission at 5577A 3. OII (2D-2P) emission at 7319-30A 4 NI (4S-2D) emission at 5200A 5. MgII(2S-2P) emission at 2802A 6. HI (n=2-3) emission at 6563A VAE may be operated in any of the following modes for geophysical data gathering. They are defined in terms of the filter wheel operation: A. Fixed wheel: Any one of eight possible filter positions. At each position a pair of atmospheric emissions is measured. One place is reserved for calibration and one for dark count information. B. Filter cycling: The filter wheel may be cycled from one position to the next at the following rates: 1) once per nadir 2) once per 2 nadir 3) once per 4 seconds 4) once per 8 seconds 5) once per 16 seconds 6) once per 32 seconds Mode 1 and 2 under B are used exclusively when the spacecraft is spinning. VAE is mounted on the spacecraft with the narrow field of view channel viewing in the -X direction and the wide field of view channel viewing in the +Y direction. For an oriented spacecraft, Ch 1 views nearly horizontally in the opposite direction to the spacecraft motion. Ch 2 views vertically upward for a spacecraft oriented normally and views in the downward direction for an inverted spacecraft. In the spinning mode both channels in one spin period, view up and down and in addition perform limb scanning experiments on each horizon. The utility of the VAE for measuring airglow emissions depends upon its sensitivity in Rayleighs/count and on the ability to determine background emissions (e.g. galactic emissions) and dark count. Appendix 1 is a tabulation of sensitivities for the 3 experiments for various temperatures. To accomplish the latter, a period of several seconds is used at the beginning of a data taking sequence to measure the dark count of each tube by inserting the dark filter wheel position in place. This procedure is again repeated just before turnoff. A very accurate determination of dark count can then be made by averaging a large number of integration periods during the sequences. Appendix 2 gives dark counts/IP for each instrument as a function of temperature. The galactic emission contaminates all data taken when viewing above the solid earth. However, it is only important when viewing emissions of intensity less then 50 Rayleighs. A careful determination of the galactic background emission, however, can be rewarding as volume emission rates of 0.1 ph cm-3 sec-1 can be deduced with 30% statistical accuracy. II. Scientific Results from the Visible Airglow Experiments Information obtained by the Visible Airglow Experiments on AE-C, -D, and -E has led to an increased understanding of the photo- chemistry of metastable constituents in the thermosphere. The com- bination of airglow data with simultaneous composition measurements has quantified numerous rate coefficients and, in some cases, has pointed to the existence of sources for metastable species which were unknown prior to the AE program. In addition, the studies have demonstrated the utility of data taken by satellite platforms in deducing reaction rates for use in atmospheric calculations. Such esperimental config- urations are free from some of the problems encountered in the lab- oratory. Studies by the VAE group have produced the following results per- tinent to the photochemistry of the thermosphere. Analysis of the 6300A red line emission from the 1D term of atomic oxygen has produced a quenching rate for O(1D) by N2 which is considerably smaller than early laboratory results, but which is reasonably consistent with more recent work (Hays et al., 1977). The magnitude of the green line feature from O(1S) at 5577A as measured by VAE required a new source in addition to those used in previous work (Frederick et al.,l976). Studies carried out prior to AE did not have simultaneous sets of composition data to use in conjunction with the airglow. The necessity to use model atmospheres introduced large uncertainties and masked the presence of the additional source. The magnitude and twilight variation of the emission indicated that the reaction N + O2+ -> NO+ + O(1S) was operative (Frederick et al., 1977). The 7319-7330A volume emission rate profile discussed by Walker et al.(1975) and Rusch et al.(1977) indicated that both N2 and O were effective in quenching the metastable ion O+(2P) The 5200A emission from the metastable nitrogen atom, N(2D) is sufficiently bright that it must be produced at near unit efficiency in the F- region. Frederick and Rusch (1977) derived values for rate coeffi- cients which control N(2D) loss. The loss rate due to reaction with O2 is in good agreement with laboratory results, however, the deduced rate coefficient for N(2D) quenching by atomic oxygen is much smaller than the current value from the laboratory. Calculations based on N(2D) loss rates similar to those discussed above by Rusch et al., 1975 indicate that the N(4S) concentrations in the altitute range 200-250 km are of order 10**7 cm-3, much larger than the NO concentration. The 3371A emission from the C3 PI term of N2 is excited exclusively by photoelectrons and the downward transition is radiatively allowed. Analysis of several orbits by Kopp et al. (1977) showed that the mag- nitude of the 3371A emission rate increases as the ratio of atomic oxygen to molecular nitrogen decreases. This is interpreted as being due to the competition between O and N2 as sinks of photoelectron energy. The remote sensing capabilities of the VAE instrument allow monitoring of airglow features which originate at altitudes well below that of the satellite. Wasser et al. (1976) employed green line, 5577A, data obtained in a slow spinning mode to conclude that the Chapman mechanism, O + O + O -> O2 + O(1S) is a more likely mechanism for exciting O(1S) than the two step process O + O + M -> O2* + M followed by O2* + O -> O2 + O(1S) in the altitude range 90 to 110 km. Airglow emission from high latitudes provide a powerful tool for studying phenomena associated with electrodynamic processes and particle precipitation. Comparison of the 4278A surface brightness from N2+(B2 SIGMA) with the electron flux measured simultaneously in the aurora confirmed the constancy of their ratio (Kasting and Hays, 1977). This provides an effective means of estimating particle energy deposition by monitor- ing auroral emissions. Data taken near the base of the dayside polar cusp region of the magnetosphere show a close correlation between particle influx, changes in atmospheric neutral composition, and airglow enhance- ments (Frederick, 1977). The polar cusp appears as a column of enhanced airglow near 75 to 76 degrees magnetic latitude with peak emission originating near 260 km in altitude. Analysis of auroral observations from VAE by Hays and Anger (1976) has led to the development of new techniques for removing surface and cloud albedo effects from satellite data. III DATA RECORDS VAE's data is in unlts of RAYLEIGHS. For oriented orbits, Channel 1 is always looking back and channel 2 is looking either up or down (the direction of ch 2 is constant over an orbit) Channel 1: RAYLEIGHS = SUM (CNTi - BACKGRNGi) *SENS/N i=(1,N) Channel 2: RAYLEIGHS = SUM (CNTi - BACKGRNGi)*|COS(ZNi)| *SENS/N i=(1,N) where CNTi= VAE photometer count as picked up from the telemetered data BACKGRNi= Dark count of instrument at time count i is taken. Computed from instrument temperature. SENS= Sensitivity of instrument in RAYLElGHS per count. ZNi= Zenith angle CH2 makes with the local vertical when count i is taken N= 32 for CH2, fixed filter wheel. This corresponds to 4 seconds = 125 for CH1, fixed filter wheel. This corresponds to 4 seconds = 8 for CH2, MODE=S4S, corresponding to 1 second. = 32 for CH1, MODE=S4S, corresponting to 1 second. = 16 for CH2, MODE=S8S, corresponting to 2 second. = 64 for CH1, MODE=S8S, corresponting to 2 second. United Abstract data values are obtained every 15 seconds by linearly interpolating data taken as defined above either side of the 15 second point. For spinning orbits both CH1 and CH2 are spinning about the satellite axis. VAE stores data taken from all four directions on CH1 and from up and down only on CH2. UP and DOWN data for CH1 and CH2 is obtained as follows. Above 200 km UP data is collected and averaged over a window centered about the vertical and extending 45 degrees on either side of it as the VAE instrument is looking away from the earth. DOWN data is collected and averaged in the same manner as the satellite is looking towards the earth. Below 200 km the perigee effects begins to contaminate the data. An attempt is made to remove from the averaging process the data counts looking between 20 degrees backwards to 45 degrees backwards in both the up and the down averaging. In all cases: RAYLEIGHS = SUM (CNTi - BACKGRNGi)*|COS(ZNi)| *SENS/N i=(1,N) where CNTi, BACKGRNDi, ZNi, SENS are defined as for oriented data and N is the number of counts collected within the up or down window. The forward and backward looking data from channel 1 for spinning orbits is calculatet differently. Data is collected in a window centered about 90 or 270 degress and extending 20 degrees on either side (i.e., 70 to 110 degrees or 250 to 290 degrees) in the form counts NS zenith angle. This defines a function COUNT (ZN) in the domain (70, 110) or (250, 290). This function is smoothed, then the smoothed data is used to fit the second order expansion about 9O or 270 degrees, e.g., COUNT(ZN) = COUNT(PI/2) + dCOUNT/dZN * 2/PI * (ZN-PI/2) + + 1/2 * d2COUNT/d2ZN * 2/PI * (ZN-PI/2)**2 RAYLEIGHS at PI/2 is taken to be COUNT(PI/2) * SENS No attempt is made to correct for perigee effect so data below 200 km is suspect in the forward direction. United Abstract data values for spinning orbits are obtained every 15 seconds by linearly interpolating data taken as discussed above on either side of the 15 second point. APPENDIX Wavelength in angstroms observed on channels 1 and 2 tabulated as a function of instruments mode (fixed filter wheel) VAE-C Wavelength Wavelength Mode on channel 1 on channel 2 ------------------------------------------------------------ 55F6 5577 6300 73FD 7319 NO DATA 33F5 3371 5577 52F7 5200 7319 42F3 4278 3371 CLF5 NO DATA 5200 63F4 6300 4278 VAE-D Wavelength Wavelength Mode on channel 1 on channel 2 ------------------------------------------------------------ 73F4 7319 4861 52FD 5200 NO DATA 55F7 5577 7319 42F5 4278 5200 63F5 6300 5577 CLF4 NO DATA 4278 48F6 4861 6300 VAE-E Wavelength Wavelength Mode on channel 1 on channel 2 ------------------------------------------------------------ 73F6 7319 6563 52FD 5200 NO DATA 55F7 5577 7319 28F5 2800 5200 63F5 6300 5577 CLF2 NO DATA 2800 65F6 6563 6300 AE-VAE BIBLIOGRAPHY Frederick, J. E. and D. W. Rusch, On the chemistry of metastable atomic nitrogen in the F-region deduced from simultaneous satellite observations of the 5200A airglow and atmospheric composition, J. Geophys. Res., in press 1977. Frederick, J. E., D. W. Rusch, G; A. Victor, W. E. Sharp, P. B. Hays ant H. C. Brinton, The OI (A5577A) airglow: Observations and excitation mechanisms, J. Geophys. Res, 81, 3923, 1976. Frederick, J. E., D. W. Rusch and S. C. Liu, Nightglow emissions of OH(X2pi): Comparison of theory and measurements in the (9-3) band, J. Geophys. Res, submitted 1977. Hays P. B., G. R. Carignan, B.C. Kennedy, G. G. Shepherd and J. C. G. Walker, The visible airglow exeriment on Atmosphere Explorer, Radio Sci., 8, 369, 1973. Hays P. B. and C. D. Anger, The Influence of ground scattering on satellite auroral observations, manuscript in preparation l976. Hays, P. B., R. G. Roble, D. W. Rusch, M. R. Torr, J. C. G. Walker, The OI(6300A) dayglow, J. Geophys. Res., submitted 1976. Kasting, J. Y. and P. B. Hays, A comparison of N2 and 4278A emission and electron energy flux in the auroral zone, J. Geophys. Res., submitted 1977. Kopp, J. P., D. W. Rusch, R. G. Roble, G. A. Vlctor and P. B. Hays, Photoemission in the second positive system of molecular nitrogen in the Earth's dayglow, J. Geophys. Res., 82, 555, 1977. Kopp, J. P., J. E. Frederick, D. W. Rusch and G. A. Victor, Morning and evening behavior of the F-region green line emisslon: Evidence concerning the sources of O(1S), J. Geophys. Res., in press 1977. Orsini, N., D. G. Torr, H. C. Brinton, L. H. Brace, A. O. Nier and J. C. G. Walker, Quenching of metastable 2D oxygen ions in the thermo- sphere by atomic oxygen, J. Geophys. Res., submittet 1977. Rusch, D. W., A. I. Stewart, P. B. Hays and J. H. Hoffman, The NI(5200A) dayglow, J. Geophys. Res., 80, 2300, 1975. Rusch, D. W., A. I. Stewart, P. B. Hays and J. H. Hoffman, Correction, J. Geophys. Res., 81, 295, 1976. Rusch, D. W., D. G. Torr, P. B. Hays and M. R. Torr, Determination of the O+(2P) ionization frequency using satellite airglow and neutral composition data and its implications on the EUV solar flux, Geophys. Res. Lett., 3, 537, 1976. Rusch, D. W., D. G. Torr, P. B. Hays and J. C. G. Walker, The OII(7319-7330A) dayglow, J. Geophys. Res., 82, 719, 1977. Rusch, D. W., D. G. Torr, M. R. Torr, N. Orsini, L. H. Brace, H. C. Brinton, W. B. Hanson, J. H. Hoffman, A. O. Nier and N. W. Spencer, The charge exchange reaction of metastable O+(2D) ions with molecular oxygen as a source of is in the thermosphere, Geophys. Res. Lett., submitted 1977. Torr, D. G., W. B. Hanson, P. B. Hays, A. E. Hedin, J. H. Hoffman, K. M. Mauersberger, D. W. Rusch, M. R. Torr and J. C. G. Walker, Reactions of metastable species as sources of atomic nitrogen ions in the thermosphere, J. Geophys. Res., submitted 1976. Torr, D. G., M. R. Torr, D. W. Rusch, P. B. Hays, K. M. Mauersberger, J. C. G. Walker, N. W. Spencer, A. E. Hedin, H. C. Brinton, R. P. Theis, Atomic nitrogen densities in the Thermosphere, Geophys. Res. Lett., 3, 1, 1976. Torr, M. R., G. R. Burnside, P. B. Hays, A. I. Stewart, D. G. Torr and J. C. G. Walker, Metastable 2D atomic nitrogen in the mid-latitude nocturnal ionosphere, J. Geophys. Res., 81, 531, 1976. Whlker, J. C. G., D. G. Torr, P. B. Hays, D. W. Rusch, R. Docken, G. A. Victor and M. Oppenheimer, Metastable 2p oxygen ions in the daytime thermosphere, J. Geophys. Res., 80, 1026, 1975. Wasser, B., D. W. Rusch, W. E. Sharp, P. B. Hays and G. R. Carignan, Evidence for the source of the mesopause OI(5577A) emission, J. Geophys. Res., submitted 1976. Not included in the bibliography are the following short papers which will appear in the Proceetings of the Atmosphere Explorer Symposium, held at Bryce Mountain, Virginia October 27-29, 1976. Frederick, J.E., The polar enhancement of airglow and molecular nitrogen: Implications for high latitude energy sources in the thermosphere. Frederick, J.E., J.P. Kopp, and D.W. Rusch, Excitation mechanisms for the F-region green line deduced from the visible airglow experiment. Hays, P.B., The role of metastable atoms and ions in the thermosphere. Hays, P.B., The 6300A airglow and molecular nitrogen quenching. Ropp, J.P., D.W. Rusch, R.G. Roble, G.A. Victor, and P.B. Hays, Photoemission in the second positive system of molecular nitrogen in the earth's dayglow. Rusch, D.W., and J.E. Frederick, Metastable atomic nitrogen in the earth's thermosphere and implications on odd nitrogen inter- conversion processes. Rusch, D.W., D.G. Torr, P.B. Hays, M.R. Torr, and J.C.G. Walker, The metastable oxygen ion, O+(2P): Its airglow, and the implication of its photochemistry on the EUV solar flux. APPENDIX 1: VAE Sensitivity The sensitivity of the VAE-C, -D, -E instruments are given in Rayleighs/count for each channel as a function of temperature. VAE-C Channel 1 T(C degree) WAVELENGTH (Angstroem) 3371 4278 5200 5577 6300 7319 ------------------------------------------------------------------------ -20 35.2 10.7 12.2 20.0 23.6 101.5 -10 35.3 10.4 11.5 19.6 20.7 79.3 0 35.8 10.6 11.1 19.4 19.2 66.8 10 36.7 10.9 11.0 19.4 18.6 57.3 20 37.9 11.4 11.1 19.9 18.4 51.1 30 39.4 12.1 12.0 21.8 18.6 45.9 40 41.4 12.8 13.5 24.4 19.6 44.2 Channel 2 -20 0.61 0.15 0.15 0.24 0.30 1.45 -10 0.61 0.15 0.14 0.24 0.27 1.13 0 0.62 0.15 0.14 0.23 0.25 0.95 10 0.64 0.16 0.14 0.23 0.24 0.82 20 0.66 0.17 0.14 0.24 0.24 0.73 30 0.68 0.17 0.15 0.26 0.24 0.65 40 0.72 0.19 0.17 0.29 0.25 0.63 VAE-D Channel 1 T(C deg.) WAVELENGTH(A) 4278 4861 5200 5577 6300 7319 ------------------------------------------------------------------------ -20 26.0 9.7 7.6 12.2 22.2 80.0 -10 24.2 8.5 7.6 11.3 17.6 72.1 0 23.3 8.2 7.9 11.1 16.7 68.5 10 23.5 8.1 8.4 11.1 16.3 72.1 20 24.4 8.1 9.6 11.1 16.4 77.8 30 26.2 8.1 12.2 11.2 19.7 87.3 40 29.2 8.3 16.3 11.6 20.4 106.6 Channel 2 -20 0.37 0.13 0.10 0.14 0.24 0.76 -10 0.34 0.12 0.10 0.13 0.19 0.69 0 0.33 0.11 0.10 0.13 0.18 0.65 10 0.33 0.11 0.11 0.13 0.18 0.69 20 0.34 0.11 0.12 0.13 0.18 0.74 30 0.37 0.11 0.16 0.13 0.21 0.83 40 0.41 0.11 0.21 0.13 0.22 1.02 VAE-E Channel 1 T(C deg.) WAVELENGTH(A) 2800 5200 5577 6300 6563 7319 ------------------------------------------------------------------------ -20 2.1 11.0 12.7 19.8 22.8 124.4 -10 2.1 10.3 12.7 19.6 21.2 88.8 0 2.0 10.1 13.2 20.4 20.4 73.7 10 2.0 10.1 15.8 22.5 20.7 61.7 20 2.0 10.4 21.8 24.2 21.3 53.9 30 2.0 11.7 29.3 46.2 22.8 47.2 40 1.9 14.1 42.4 73.8 29.3 44.2 Channel 2 -20 0.03 0.15 0.16 0.23 0.26 1.27 -10 0.03 0.14 0.16 0.23 0.24 0.91 0 0.03 0.14 0.16 0.24 0.23 0.76 10 0.03 0.14 0.19 0.26 0.23 0.63 20 0.03 0.14 0.27 0.29 0.24 0.55 30 0.03 0.16 0.36 0.54 0.26 0.48 40 0.03 0.19 0.52 0.86 0.33 0.28 APPENDIX 2: Dark count/I.P. vs. Temperature VAE-C VAE-D VAE-E ----- ----- ------- T(C deg.) ch 1 ch 2 ch 1 ch2 ch 1 ch 2 -20 0.02 0.01 0.00 0.00 0.00 0.04 -10 0.11 0.08 0.01 0.03 0.03 0.24 0 0.50 0.45 0.04 0.14 0.13 1.38 10 2.34 2.57 0.22 0.73 0.78 8.01 20 10.95 14.81 1.16 3.92 4.40 46.50 30 51.27 85.20 6.17 20.98 25.49 269.99 40 240.13 450.29 32.41 112.25 147.70 -