Portable Broadband SeismologyJakarta, IndonesiaMay 11-13, 2006

Bruce BeaudoinMarcos AlvarezPart 9: Sensor Quality Control

Broadband SeismometersGuralp CMG-3TStreckeisen STS-2

Guralp CMG-3TOrthogonal elements2 Horizontal1 Vertical

Guralp CMG-3TVertical Element PivotHorizontal Element Pivot

Streikeisen STS-2

TransformationEquationsEastNorthVertical

Element Contribution to Signal

STS-2 Element W problemZNEZNE

STS-2 Element V problemZNE

RefSTSAE

N

ZE

N

ZObvious Problems With Time SeriesSTS-2 With Bad Element V Hinge

Inadequate Vault

Pier Test - Simultaneous recording of - 3 CMG-40T E/W compOdd 40T

Response to White Noise Calibration InputAmplitudeFrequency40T-30secOdd 40T

STS-2 Flooded On Day 3 After InstallationDay 2 Day 3 F 7

F 10Electronic Noise? Bad Cable?Note teleseism overwhelms the noise on day 4

F 12Unexplained Intermittent Monochromatic Noise

Figure 5B.Glitches from the noisy day in Figure 5A illustrate a problem with Element W (refer back to Figure 4). One cannot make a definite diagnosis of the problem from these data. Sometimes it will be clear when the sensor is opened and examined that the problem is one or more of the hinges in element W, but leaky capacitors could also create this type of noise. Fixing sensors is often a trial-and-error process.

Figure 6.Another example of a noisy STS-2. This one is showing a problem with Element V (expanded in the bottom frame).Figure 3. All three components of STSA from previous figure compared to the Reference time series (about 9 hours of data) recorded simultaneously. STS1 was subsequently repaired by replacing a bad hinge in the V Element.Figure 11.Five days, 3 components each showing mirror-like horizontal noise and a very long-period vertical response. This noise is probably the result of an inadequate vault.NOT ALWAYS visible in time series alone.PASSCAL Pier test showing one CMG40T with the wrong response. Top 3 traces: E/W comp of side-by-side40Ts (all supposed to have a 30-sec corner). Bottom: Fast Fourier spectra - blue trace shows 40T with wrong frequency response. See next figure.Figure 1B.White Noise calibration: comparison of the erroneous (Odd) 40T E & N comps with a normal 40T. The original calibration of the odd 40T (s/n T4E04) did not have the odd response (approx 70-sec corner). Therefore sometime during the sensors lifetime its response changed. It had been to 2 Antarctic experiments - I wonder if cold may have affected it, but I dont know. The PI who had the bad 40T immediately prior to the pier test where it was discovered, has been informed. WARNING! That doesnt mean his metadata is correct yet at the DMC, because we did not give him poles and zeros for the odd 40T.Figure 7.Illustration of a flooded STS-2, 2 and 3 days after it was installed in Costa Rica. The vault was constructed to be a diving bell, using the pressure of the volume of air in the sensor housing to keep water from filling it. The sensors pedestal, however, was not high enough to keep the STS-2, in particular its connector, from submerging.Fortunately, the sensor was rescued within hours of discovering these nasty-looking waveforms on Day 3.Figure 10.Noisy data, cause unknown. Cable problem? Sensor electronics?Four days shown, 3 components per day. A teleseism on day 4 overwhelms the noise.Figure 12.Mystery noises. Nearly monochromatic, comes in bursts (top frame), one of which is expanded showing its time- and frequency-domain character (middle and bottom frames).