Measurement of Neutral Atmosphere Density During the Years of Increasing Solar Activity Using \textit{Insight}-HXMT Data with the Earth Occultation Technique

TL;DR

This study uses the Earth Occultation Technique with extit{Insight}-HXMT data to measure Earth's atmospheric density during increased solar activity, comparing results with the NRLMSIS model and identifying overestimations at certain altitudes.

Contribution

It introduces a novel method combining EOT and Maximum Likelihood Estimation to estimate atmospheric density from X-ray observations during occultation events.

Findings

Agreement with NRLMSIS model at specific altitudes during high solar activity

NRLMSIS overestimates density by about 20% at certain altitudes

Measurement bias at lower altitudes prevents accuracy assessment there.

Abstract

The density of the Earth's middle and upper atmosphere is an important question in Earth science and is a critical factor in the design, operation, and orbital determination of low Earth orbit spacecraft. In this study, we employ the Earth Occultation Technique (EOT) combined with Maximum Likelihood Estimation to estimate the neutral atmospheric density by modeling the attenuation of X-ray photons during the occultation process of \textit{Insight}-HXMT observations of Crab Nebula. Based on 83 occultation datasets of the Crab Nebula observed by all three sets of telescopes of \textit{Insight}-HXMT between 2022 and 2024, we derived the atmospheric densities at altitudes ranging from 55\,--130\,km. We find a general agreement between our results and the prediction by the NRLMSIS model within the altitude ranges of 65\,-- 90\,km, 95\,--100\,km and 120\,--130\,km, particularly during periods of enhanced solar activity. However, we also find that the NRLMSIS model overestimates atmospheric density at altitudes 90\,--95\,km and 100\,--120\,km by approximately 20\%. Furthermore, since the atmospheric density measurements at altitudes of 55\,--\,65\,km may be subject to selection bias, we do not report the prediction accuracy of the NRLMSIS model at this altitude.