Julia Kruck and I buried the high-sensitivity LEMI magnetometers this week near the vault.  This is at the approximate location for which trial spectra were taken (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=12525), and determined to be good enough to study subtraction of the effects of globally correlated fields due to, for example, Schumann resonances.

We buried them directly in the soil at a depth of about 18 inches. We used a bubble level to ensure that they were not tilted in Z, and aligned them with beam tube X and Y using lines constructed and measured on Google satellite images. We think that this alignment technique was more accurate than could be made with the simple compass that we had, though we made sure that the compass agreed with our alignment.  The connector to the X-axis magnetometer is 17m in the -X-direction from the  +Y corner of the electronics vault, and the magnetometer extends in the -X direction beyond the connector (see photos). The Y-axis magnetometer has its connector 1.22 meters +X and 1.22 m -Y of the connector for the X-axis magnetometer, so the closest parts of the magnetometers, the connectors, are 1.72 m apart. The connector  is on the +X or +Y end of the magnetometers so that the signals will have the proper phase relationship. 1.22 meters of cable is buried directly in the ground before the point where the cables come together to enter the conduit (yet to be installed) in order to damp any cable vibrations. The LEMIs lie between the lines of orange stakes that parallel them to either side (see photos). The electronics had not arrived so they have not yet been tested.

Absolute location: X-axis magnetometer  is 1020 m +X,  188 m +Y of the vertex

Robert Schofield, Julia Kruck