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Entry  Sun May 30 22:18:49 2010, rana, Update, PEM, Granite slab w/ lead balls is so far a flop 
    Reply  Mon May 31 22:52:57 2010, rana, Update, PEM, Granite slab w/ lead balls is so far a flop Untitled.pnghuddlez.pnghuddlez.png
Message ID: 3022     Entry time: Mon May 31 22:52:57 2010     In reply to: 3018
Author: rana 
Type: Update 
Category: PEM 
Subject: Granite slab w/ lead balls is so far a flop 

This plot shows the noise with the box on, but no granite. We're still pretty far off from the Guralp data sheet.

Untitled.png

I implemented software rotation in the huddle subtraction as Valera suggested and it works much better. The two plots below show the before and after. So far this is just 2 deg. of rotation around the z-axis. I'm assuming that aligning the seismometers vertically via bubble level is good enough for the z-axis, but I haven't calibrated the bubble yet.

huddlez.pnghuddlez.png

The residual slope is now suspiciously smooth. I somehow suspect that our readout electronics can still be responsible. We need to hook up a 9V battery to the input terminals to check it out. Its a little steeper than 1/f and I thought that we had exonerated the Guralp breakout box in the past, but now I'm not so sure. I'll let Jenne comment on that.

I also noticed that we have not yet divided by sqrt(2) to account for the fact that we are subtracting 2 seismometers. In principle, an unbiased estimate of the single seismometer noise will be lower by sqrt(2) than the green curve.

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