Michael, Krishna

Today, we changed some parameters which correct for pixel-level non-linearities in the CCD. This improved the noise in the BRS-2 output.

We also improved several error-handling features of the code and created the Status signal (the 4th channel going in to SEI), which is set to have the following states: Good (5V), Damping On (2V) and Bad (0V). In the near future, there will be several other more detailed states on the BRS model screen indicating the specific problem, if it is in a bad state, which will help debug the problem. Detailed documentation on this will be prepared soon. We also filled out some of the filter banks for processing the BRS-2 data and for tilt-subtraction. More on that in the future.

The first attachment shows the BRS-2-rX signal in comparison to the STS2-Y seismometer on the ground close to it. The data is converted in to displacement units and was measured with low wind speeds on the order of 2-3 mph. The next page shows the coherence between the sensors. The instrument is still drifting and settling, so the low-frequency noise will improve over time.

We noticed that there may have been some excess noise in BRS-2, especially at higher frequencies, due to aliasing from the high frequency spikes (30, 80 Hz). Therefore we lowered the software low-pass corner frequency from ~50 Hz to 10 Hz. This does introduce phase-loss at ~few Hz but since this sensor is primarily used at ~10-500 mHz, this shouldn't be a problem.

The second attachment shows the output of BRS-2 after the improved low-pass.