SFT data preparation using GEO E7 dataSFT data preparation using GEO E7 data

m.alessandra papa

max planck institut f. gravitationasphysik

What time baseline ?What time baseline ?

• in principle the longer the better and the constraint comes from highest intrinsic search frequency that you want to search for

• in practice, if you want consecutive stretches of data during which the detector was in-lock as input to your FFT routines and if the detector is not always in-lock, longer time baseline means reducing the amount of data that you consider

What time baseline ?What time baseline ?

60 seconds in order to get 72% of data60 seconds in order to get 72% of data

Why did we decide not to padWhy did we decide not to pad

• if you pad with zeros you exploit the data best but you waste computational power in the Demod

• if you pad with the average value of the noise you waste computational power and you add noise in the filtering.

• if you require continuous stretches of data, the SFTs are simpler objects, you may throw away some data but you can minimize this by going to shorter time baselines. In turn this enhances the computational load in Demod.

The E7 GEO SFTsThe E7 GEO SFTs

• A complete copy of all GEO data from E7 run was stored in Hannover and at the AEI. Frame servers were running at both locations and data could be easily downloaded on-line (channel x from time t1 to time t2) using M. Hewtson’s software GEOTOOLS from remote locations.

• During E7 we have lost some data: total of 1 minute.

• Based on quality-channel 1s average trend-data, the 60s stretches where selected.

• A timestamp list was created: 15505 entries – roughly 10 days, starting on Jan 1 at 00:00

The timestampsThe timestampsMaximum out-of-lock: 3.8 hours

The SFT formatThe SFT format

• Simple binary format first set up for driver of Hough hierarchical code:

FFT Data

Re

Im

Re

Im

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header 32 bytes:

REAL8 endian

INT4 gps_sec

INT4 gps_nsec

REAL8 tbase

INT4 firstfreqindex

INT4 nsamples

1

2

nsamples

There’s only few relevant standard commands: fopen, fclose,fread,fwrite,fseek.

1283.4

A Power Spectral Density figure derived A Power Spectral Density figure derived from one of the SFT filesfrom one of the SFT files

sampling: 16384 Hz, calibrated hoft channel, 983040 samples

100 SFTs, sqrt(power spectr. density)

1e-19

1e-18

1e-17

1e-16

1283.4 Hz 1284.4 Hz1283.4

Six power spectral density plot from Six power spectral density plot from consecutive SFTs consecutive SFTs

It’s the system settling back after loss of It’s the system settling back after loss of lock.lock.

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