### Question
How is the term upper atmosphere defined?


### Answer
The term **upper atmosphere** is defined in *51 U.S.C. § 20162* as the following:

> that portion of the Earth's sensible atmosphere above the troposphere

#### Citation:
  - *51 U.S.C. § 20162*
  - Heading: **Subtitle II-General Program and Policy Provisions > CHAPTER 201-NATIONAL AERONAUTICS AND SPACE PROGRAM > SUBCHAPTER IV-UPPER ATMOSPHERE RESEARCH**

