gravitational wave advanced detector workshop – aspen (co) - jan. 16 - 22, 2005 seismic noise...
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Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Seismic Noise Coherence Measurements in Deep Salt Mines
F. Acernesea, F. Baroneb, R. Burnsc, G. Cellad, R. De Rosaa, F. De Salvoe, R. De Salvof, S. Menegonf, L. Milanoa, G. Pelleritof, J.
Strandsc
aUniversità di Napoli “Federico II”bUniversità di Salerno
cCalifornia State University- PomonadINFN – Sezione di Pisa
eRealmonte ItalkalifLIGO – Caltech
LIGO-G050053-00-Z
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
OverviewOverview
• Introduction
• Realmonte salt mine
• Measurement Set Up
• Results
• Next Step
• Conclusions
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
IntroductionIntroduction
One of the main problems involved in developing high sensitivity terrestrial interferometer for gravitational waves is the contribution of the newtonian noise in the low frequency region.
A partial solution to this problem can be obtained by building new detector underground in order to reduce the effect due to the surface waves.
In addition it is possible to arrange a set of seismic sensors in order to monitor and subtract the contribution of the newtonian noise from the interferometer output.
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
IntroductionIntroduction
To verify these hypothesis we perform a seismic noise data acquisition in a deep salt mine
The preliminary results of this survey are reported and the future foreseen steps.
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Realmonte Salt MineRealmonte Salt MineThe Realmonte salt deposit is located on the Southern coast of Sicily, about 4 km from
Agrigento and 1 km from Porto Empedocle.
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Realmonte Salt MineRealmonte Salt Mine
The layers of rock salt and kainite run underground in a line dropping from mountain to sea, with the rock salt layer acting as a roof to the kainite to a depth of 40 meters and a presence of NaCl of 97-98% pure.
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Measurement Set UpMeasurement Set Up
The measurement of the seismic noise inside the mine was performed using triaxial accelerometers model FBA ES-T (Episensors) from Kinemetrics:
Sensitivity: 40V/g
Bandwidth: 0.1 – 200 Hz
10-1
100
101
102
-20
-10
0
10
Frequency (Hz)
Ma
gn
itud
e (
dB
)
10-1
100
101
102
-200
-100
0
100
200
Frequency (Hz)
Ph
ase
(d
eg
ree
s) Frequency (Hz)
Am
plit
ude
(dB
)
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Measurement Set UpMeasurement Set Up
The data coming from the episensor were acquired by using a VME based digital acquisition system composed by:
- 1 CPU board running LynxOs;
- 1 ADC board with 8 input channels and 16 bit resolution;
- 2 SCSI Disks, 9 Gb size, for storing data.
In order to match the episensor output and the ADC input dynamic ranges, and to avoid aliasing problems, a conditioning electronics with an amplifying (G=100) element and a filtering element (8th order Chebyshev filter with cut off at 200 Hz).
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Measurement Set UpMeasurement Set Up
Each acquisition system was used to manage two episensors.
10-1
100
101
102
103
-100
-50
0
Frequency (Hz)
Ma
gn
itud
e (
dB
)
10-1
100
101
102
103
-200
-100
0
100
200
Frequency (Hz)
Ph
ase
(d
eg
ree
s)
ADC Board
CPU Board
Conditioning
Electronic
Epi 1
Epi 2
Oscillator F=800Hz
Storage Disk
VME bus
A local oscillator was used to provide the trigger for data acquisition. (No external synchronization)
SCSI bus
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Measurement Set UpMeasurement Set Up
The measure was carried out by placing two acquisition systems in two caves at different depth in the mine.
Level 1: -141 m
Sensors: 1A, 1B
Level 2: -128 m
Sensors: 2A, 2B
Acquisition systemsSensors
26 m
50 m
Top view
13 m
1A
2A 2B
2A
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Measurement Set UpMeasurement Set Up
A single oscillator was used to trigger both the acquisition systems, in order to synchronize at least the data with themselves.
The acquisition was carried out starting from July 7 to August 1, 2004 (26 days), with a sampling frequency of 800 Hz.
A total of 12 seismic channels plus 2 monitor channels were acquired during this period.
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
ResultsResults
Power spectral density of acceleration inside the mine (NS)
10-1
100
101
102
10-8
10-7
10-6
10-5
10-4
10-3
NS Direction
Frequency (Hz)
Acc
elle
ratio
n (m
/s2 /H
z-1/2
* )
Frequency (Hz)
Acc
eler
atio
n P
SD
(m
/s^2
/sqa
rt(H
x)
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
ResultsResults
Power spectral density of acceleration inside the mine EW
10-1
100
101
102
10-8
10-7
10-6
10-5
10-4
10-3
WE Direction
Frequency (Hz)
Acc
elle
ratio
n (m
/s2 /H
z-1/2
* )A
ccel
erat
ion
PS
D (
m/s
^2/s
qart
(Hx)
Frequency (Hz)
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
ResultsResults
Power spectral density of acceleration inside the mine (z)
10-1
100
101
102
10-8
10-7
10-6
10-5
10-4
10-3
Vertical Direction
Frequency (Hz)
Acc
eler
atio
n (m
/s2 /H
z-1/2
)A
ccel
erat
ion
PS
D (
m/s
^2/s
qart
(Hx)
Frequency (Hz)
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
ResultsResults
Searching for seismic noise sources… (PCA)
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
ResultsResults
Test of noise subtraction (multicoherence method)
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
Next StepNext Step
Arrangement of another acquisition system in a (possibly) spherical cave to optimize the noise subtraction procedure and to enhance the reduction of newtonian noise.
Sensors
Gravitational Wave Advanced Detector Workshop – Aspen (CO) - Jan. 16 - 22, 2005
ConclusionsConclusions
Building new interferometers underground can effectively enhance their sensitivity in the low frequency region.
The newtonian noise subtraction procedure can even increase this enhancement (if performed correctly).
Preliminary results on both this effects, base on experimental data, give us encouraging results.