The lower-thermosphere–ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200 km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI.

中文翻译：

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较低的热电离层（LTI）数量：测量技术和模型的当前状态

低热层-电离层（LTI）系统由高空大气层和电离层下部组成，因此包括一个与下方大气层和上方空间耦合的复杂系统。LTI的大气部分受连续流体动力学和化学定律的支配，而电离层是受磁层，太阳风和发电机驱动的电磁力控制的等离子体系统。因此，LTI是受许多不同物理过程控制的域。但是，尽管LTI距我们的行星表面仅80至200 km，但仍严重缺乏该区域内的系统原位测量。本文回顾了就地或通过几种不同的遥感方法测量LTI的最新技术。我们首先概述LTI中需要高质量现场测量的未解决问题，然后再审查直接可观察到的参数及其最重要的导数。进行此次审查的动机是由于最近将Daedalus任务保留为欧洲航天局（ESA）地球探索者10计划中的三个竞争任务候选者之一。但是，本文打算涵盖LTI参数，以便可以将其用作针对LTI现场观测的任何任务的背景科学参考。进行此次审查的动机是由于最近将Daedalus任务保留为欧洲航天局（ESA）地球探索者10计划中的三个竞争任务候选者之一。但是，本文打算涵盖LTI参数，以便可以将其用作针对LTI现场观测的任何任务的背景科学参考。进行此次审查的动机是由于最近将Daedalus任务保留为欧洲航天局（ESA）地球探索者10计划中的三个竞争任务候选者之一。但是，本文打算涵盖LTI参数，以便可以将其用作针对LTI现场观测的任何任务的背景科学参考。