Michael, Krishna,

This evening we tried using the tilt-subtracted ground sensor for sensor correction(SC) in the Y-axis on Stage 1 at EndY. Wind speeds were between 0-10 mph. We tried four configurations:

1. 90 mHz blends (Quite_90) only

2. 90 mHz blends and broadband sensor correction using BRS-2

3. 45 mHz blends only and

4. 45 mHz blends with broadband sensor correction using BRS-2.

The results are shown in the attached pdf. The first plot shows the ASD of Stage 1 T240 seismometers. As expected 90 mHz blends do not provide any isolation at the microseism, and 45 mHz blends do well there. But 90 mHz blends and SC performs nearly as well as the 45 mHz blends. The second plot shows the rms of the ST1 capacitive sensors, which is a measure of the net DC motion of the platform. 90 mHz blends + SC does a factor of ~5 better than other configurations. The third plot shows the ground motion during the four configurations and the tilt-subtracted sensor signals in each case, showing the factor of 3-5 improvement.

Bottomline: 90 mHz blends and sensor correction using BRS-2 does nearly as well as 45 mHz blends above 0.1 Hz and improves the low frequency rms by a factor of ~5, even under mildly windy conditions. We will repeat this test under higher wind conditions, where performance is expected to be even better.