An official website of the United States government
Here's how you know
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
The environmental noise spectra measured by a magnetometer with 2 mm diameter, 1st- and 2nd-order gradiometers with 22 mm diameter and 50 mm baselines. All pick up coils are wound using 80 μm diameter Nb wire.