Current Research

A New Approach for 4-D Exospheric Tomography Based on Optimal Interpolation and Gaussian Markov Random Fields (2022)

Authors: Gonzalo Cucho-Padin, Humberto Godinez, Lara Waldrop, Igor Baliukin, Dolon Bhattacharyya, David Sibeck and Michael Henderson

Exospheric tomography is a computational 3-D imaging technique that provides estimates of the neutral density distributions of the terrestrial exosphere from space-based UV measurements. Variability of neutral densities during geomagnetically active conditions has been previously reported, motivating the development of time-dependent tomographic techniques that can characterize both the spatial and temporal scales of densities during these events. However, solving the dynamic exospheric tomography problem can be challenging owing to its ill-posedness and high computational cost. In this letter, we introduce a novel algorithm for 4-D exospheric tomography based on Optimal Interpolation (OI) and Gaussian Markov Random Field (GMRF) theory. The OI analysis enables iterative reconstructions of the exosphere when a statistical background field is provided. Its mean is selected from previous knowledge of the exosphere and its covariance matrix is estimated using GMRF. To validate the performance, we apply our proposed methodology to six days of UV data acquired by NASA’s TWINS mission during the geomagnetic storm that occurred on June 15, 2008.

Citation: Cucho-Padin, G., Godinez, H., Waldrop, L., Baliukin, I., Bhattacharyya, D., Sibeck, D., Henderson, M. (2023). “A New Approach for 4-D Exospheric Tomography Based on Optimal Interpolation and Gaussian Markov Random Fields.” IEEE Geoscience and Remote Sensing Letters, vol. 20, pp. 1-5. doi.org/10.1109/LGRS.2023.3237793

The Earth’s Outer Exospheric Density Distributions Derived from PROCYON/LAICA UV Observations (2022)

Authors: Gonzalo Cucho-Padin, Shingo Kameda and David Sibeck

Current three-dimensional, data-based models for the terrestrial exosphere have been derived from measurements of optically thin Lyman-alpha (Ly-α) emissions scattered by neutral hydrogen atoms. Such models are only valid for the middle exospheric region (3-8 Earth radii geocentric distances) since the orbital paths of the space-based platforms used to acquire Ly-α radiance were located within the exosphere, thus precluding the proper detection of the faint outer exospheric emission. Notwithstanding, accurate specifications of density distributions beyond 8 RE are needed to support comprehensive studies of the solar-terrestrial interactions. Two upcoming missions, the Solar wind Magnetosphere-Ionosphere Link Explorer (SMILE) and the Lunar Environment Heliospheric X-ray Imager (LEXI), will image the Earth’s magnetosheath in soft X-rays, and neutral densities are crucial to extract ion distributions through inversion of the acquired images. This work develops a technique to estimate the Earth’s outer exospheric density distributions using far-ultraviolet wide-field data acquired by the Lyman-Alpha Imaging Camera (LAICA) onboard the Proximate Object Close Flyby with Optical Navigation mission. Our approach formulates an inverse problem based on the linearity between measurements of scattered Ly-α flux and the local atomic hydrogen density, which is solved using the Bayesian approach known as Maximum a posteriori estimation. We use the LAICA image to derive global, 3-D hydrogen density distributions at 6-20 RE geocentric distances. We find that the spatial structure of the outer exosphere agrees well with the predictions of radiation pressure theory. Further, we find that the mean hydrogen density at 10 RE subsolar point is 26.51 atoms/cm3

Citation: Cucho-Padin, G., Kameda, S., & Sibeck, D. G. (2022). “The Earth’s outer exospheric density distributions derived from PROCYON/LAICA UV observations.” Journal of Geophysical Research: Space Physics, 127, e2021JA030211. doi.org/10.1029/2021JA030211