Effective Solution Algorithm for Tomographic Inversion of Volume Emission Rate from Satellite-based Limb Measurement

The volume emission rate (VER) of airglow can be used to investigate atmospheric processes. Satellite-based limb measurement of atmosphere is able to obtain the VER profile of airglow with high vertical resolution. However, the traditional one-dimensional retrieval techniques for VER inversion fail to retrieve horizontal structure of VER profile. Thus, the tomographic technique based on the maximum probability is applied to retrieving two-dimensional VER profile of airglow from infrared limb measurement. This technique could process the observed data with low signal-to-noise ratio caused by the observation angle of less than 180° due to the solid nature of the Earth. For saving the processing time and improving the computing speed of VER inversion, serial tables for storing the large sparse matrix for radiance simulation and a large dataset during iterative estimate of VER are presented. The index and weighting factor of line of sight (LOS) through each grid are saved in initial estimate to avoid being computed repeatedly. Furthermore, the product of observed radiance and corresponding weighting factor obtained in initial iteration is stored as weighted observed radiance for the iterative calculation subsequently. Based on the improved algorithm, the VER of airglow is inversed through the tomographic technique. The full width of half maximum (FWHM) of error is 1.78% and the offset of the peak percentage error is 0.22% after 40 iterations for final VER. Comparison of assumed and retrieved VER profiles suggests that VER can be retrieved with a bias of 15% between 10 km and 90 km above the LayerMin (6384 km from the Earth center), and with a bias of 8% for altitude from 30 km to 60 km with vertical resolution of 1 km after 40 iterations. After improvements, the computation speed of VER inversion for once can be improved by 29.6 times for 700 images of 1/3 orbit, and accordingly, the processing time will be reduced from 3 hours and 11 minutes to only 6 minutes. In conclusion, the improvements to tomographic inversion of VER of airglow proposed in this paper are effective and significant.

Airglow simulation based on the Atmospheric Ultraviolet Radiance Integrated Code of 2012

The Atmospheric Ultraviolet Radiance Integrated Code （AURIC） is a software package developed by Computa- tional Physics, Inc. （CPI） under the sponsorship of the Air Force Phillips Laboratory/Geophysics Directorate （PL/GP） （cur- rently the Air Force Research Laboratory） for middle and upper atmospheric radiance modeling from the far ultraviolet to the near infrared. The AURIC has been considered as a general model for the radiative transfer simulation of airglow. Based on the theory of MODerate resolution atmospheric TRANsmission （MODTRAN）, the AURIC extends calculation to altitudes above 100 km and the wavelength down to 80 nm. A package of AURIC vl.2 was released in 2002, which can be used for sin- gle-point simulation from 1947 to 1999. It means that the model is not suitable for atmospheric simulation of large datasets or for atmospheric parameters retrieval from amount of satellite measurements. In this paper, AURIC vl.2 is upgraded to AURIC-2012 based on MATLAB with improvements for modules of the Geomagnetic Parameter （GEOPARM）, Atmosphere neutral composition （ATOMS）, and Ionospheric electron density （IONOS）. The improved AURIC can be used for global au- tomatic airglow simulation and also for automatic retrieval of atmospheric compositions from satellite global observations, such as O/N2 and electron density etc. Besides, the model supplies possibilities for further improvement of airglow radiative mechanism and for substitution of other modules. Based on the AURIC-2012, Limb Column Emission Intensity （L-CEI） and Volume Emission Rate （VER） are calculated. For validation, the results were compared with measurements of the Global Ul- traviolet Imager （GUVI） and TIMED Doppler Interferometer （TIDI）, respectively. The averaged relative errors of L-CEI and VER at peak altitude are both within 20%. Finally, L-CEI varying with latitude, altitude, solar activity, and geomagnetic activ- ity is simulated, and the distribution characteristics of the simulation and their influencing factors are analyzed subsequently.