### Abstract

Inversion of space-borne remote sensing measurements of the resonantly scattered solar Lyman alpha (121.6-nm) emission in planetary atmospheres is the most promising means of quantifying the H density in a vast volume of space near terrestrial planets. Owing to the highly nonlinear nature of the inverse problem and the lack of sufficient data constraints over the large volume of space where H atoms are present, previous inversion methods relied on physics-based parametric formulations of the H density distributions to guarantee solution uniqueness. Those physical formulations, such as the Chamberlain model, were developed with simple assumptions of the atmospheric conditions. The use of such formulations as constraints significantly limits the range of possible solutions, which might lead to large errors in the case when those assumptions are invalid. In this study, we demonstrate for the first time the feasibility of estimating the H density through regularized nonlinear inversion of the Ly-α emission in an optically thick atmosphere, without using parametric formulations. Specifically, Occam's inversion algorithm is used to demonstrate that the H density can be estimated in a large volume of space near the planet, with accuracy in different atmospheric regions depending on the observation scheme. Two distinctly different schemes are examined, including a low-Earth orbit and a geostationary orbit. Modeling results show that the low-Earth orbit is better for H density estimation in the thermosphere, while the high-altitude orbit is better for estimation in the exosphere. Our results could provide useful information for designing the observation schemes of future missions.

Original language | English (US) |
---|---|

Pages (from-to) | 8641-8648 |

Number of pages | 8 |

Journal | Journal of Geophysical Research: Space Physics |

Volume | 123 |

Issue number | 10 |

DOIs | |

State | Published - Oct 2018 |

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### Keywords

- H density distribution
- Lyman alpha emission
- planetary atmospheres
- radiative transfer
- regularized nonlinear inversion
- remote sensing

### ASJC Scopus subject areas

- Geophysics
- Forestry
- Oceanography
- Aquatic Science
- Ecology
- Water Science and Technology
- Soil Science
- Geochemistry and Petrology
- Earth-Surface Processes
- Atmospheric Science
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science
- Palaeontology

### Cite this

**Nonparametric H Density Estimation Based on Regularized Nonlinear Inversion of the Lyman Alpha Emission in Planetary Atmospheres.** / Qin, Jianqi; Harding, Brian J.; Waldrop, Lara.

Research output: Contribution to journal › Article

*Journal of Geophysical Research: Space Physics*, vol. 123, no. 10, pp. 8641-8648. https://doi.org/10.1029/2018JA025954

}

TY - JOUR

T1 - Nonparametric H Density Estimation Based on Regularized Nonlinear Inversion of the Lyman Alpha Emission in Planetary Atmospheres

AU - Qin, Jianqi

AU - Harding, Brian J.

AU - Waldrop, Lara

PY - 2018/10

Y1 - 2018/10

N2 - Inversion of space-borne remote sensing measurements of the resonantly scattered solar Lyman alpha (121.6-nm) emission in planetary atmospheres is the most promising means of quantifying the H density in a vast volume of space near terrestrial planets. Owing to the highly nonlinear nature of the inverse problem and the lack of sufficient data constraints over the large volume of space where H atoms are present, previous inversion methods relied on physics-based parametric formulations of the H density distributions to guarantee solution uniqueness. Those physical formulations, such as the Chamberlain model, were developed with simple assumptions of the atmospheric conditions. The use of such formulations as constraints significantly limits the range of possible solutions, which might lead to large errors in the case when those assumptions are invalid. In this study, we demonstrate for the first time the feasibility of estimating the H density through regularized nonlinear inversion of the Ly-α emission in an optically thick atmosphere, without using parametric formulations. Specifically, Occam's inversion algorithm is used to demonstrate that the H density can be estimated in a large volume of space near the planet, with accuracy in different atmospheric regions depending on the observation scheme. Two distinctly different schemes are examined, including a low-Earth orbit and a geostationary orbit. Modeling results show that the low-Earth orbit is better for H density estimation in the thermosphere, while the high-altitude orbit is better for estimation in the exosphere. Our results could provide useful information for designing the observation schemes of future missions.

AB - Inversion of space-borne remote sensing measurements of the resonantly scattered solar Lyman alpha (121.6-nm) emission in planetary atmospheres is the most promising means of quantifying the H density in a vast volume of space near terrestrial planets. Owing to the highly nonlinear nature of the inverse problem and the lack of sufficient data constraints over the large volume of space where H atoms are present, previous inversion methods relied on physics-based parametric formulations of the H density distributions to guarantee solution uniqueness. Those physical formulations, such as the Chamberlain model, were developed with simple assumptions of the atmospheric conditions. The use of such formulations as constraints significantly limits the range of possible solutions, which might lead to large errors in the case when those assumptions are invalid. In this study, we demonstrate for the first time the feasibility of estimating the H density through regularized nonlinear inversion of the Ly-α emission in an optically thick atmosphere, without using parametric formulations. Specifically, Occam's inversion algorithm is used to demonstrate that the H density can be estimated in a large volume of space near the planet, with accuracy in different atmospheric regions depending on the observation scheme. Two distinctly different schemes are examined, including a low-Earth orbit and a geostationary orbit. Modeling results show that the low-Earth orbit is better for H density estimation in the thermosphere, while the high-altitude orbit is better for estimation in the exosphere. Our results could provide useful information for designing the observation schemes of future missions.

KW - H density distribution

KW - Lyman alpha emission

KW - planetary atmospheres

KW - radiative transfer

KW - regularized nonlinear inversion

KW - remote sensing

UR - http://www.scopus.com/inward/record.url?scp=85054591068&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85054591068&partnerID=8YFLogxK

U2 - 10.1029/2018JA025954

DO - 10.1029/2018JA025954

M3 - Article

AN - SCOPUS:85054591068

VL - 123

SP - 8641

EP - 8648

JO - Journal of Geophysical Research D: Atmospheres

JF - Journal of Geophysical Research D: Atmospheres

SN - 0148-0227

IS - 10

ER -