True-North Alignment on the Field: From a Compass to an Optical Gyrocompass

Session: Recent Advances in Very Broadband Seismology [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

To install a seismometer with a properly defined orientation - inside a vault or into a borehole - as a single station including various instruments or as a part of an array - an ‘adequate’ tool is needed. This tool must achieve different functions, the first being to aim True-North with a reliable accuracy, but it is not the sole function. Indeed, compasses of any kind always measure their own orientation, so the questions on the field are always: how to make the orientation of the compass becomes the orientation of the sensor you are installing and with how much added uncertainty.

Starting with basics about the definition of magnetic Norht declination and the reason why North heading is express in secant latitude, the presentation will explain how an optical gyrocompass infers from both earth rotation rate vector and gravity vector the direction of the True North.

Then, improvement of the navigation algorithm recently made to get a faster and more reliable heading using Quadrans gyrocompass from iXblue will be presented. Indeed, optimization was feasible taken into account that in this particular application Quadrans is used statically on the field. Experimental results from this work will be disclosed and explained.

An exhaustive study of the different ways to transfer the orientation the compass to the sensor to align will be presented and corresponding added uncertainty will be evaluated, which is a good way to promote good practice on the field.

Finally, some figures will be gathered and shared from literature to quantify the precision needed for the alignment of a seismic sensor. There are today so few papers about this important matter that it is worth to spread their information.

Presenting Author: Nathalie Olivier

Authors