UVW Analysis and Recentering FVM Broadband
September 6, 2017

Introduction

We noticed some odd behavior in the seismogram displays for the FVM broadbands. First the N and E channels had a long period noise. Second the digital counts were very high. Recall that for a 24 bit digiizer, the range of maximum count should be on the order of +-8,000,000.

The figure illustrates the problem and also the corrective action that was applied at about 17:15.

Analysis

The BH channels waveforms were extracted from the CWB and then displayed. Since the sensor was a Trillium, they were rotated to the internal UVW channels using the gsac command rot3 to uvwtril


Original traces. The large DC offset makes it seem as if the E and Z channels are constant.	Result of converting to UVW. Here we see that the U channel has the large DC offset

Resolution

A remote centering command was issued to the sensor. The latter part of this seismogram display shows that the centering resolved the large offset and that traces no longer exhibit the long period noise.