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Evolution of type of measurement and of Data format

Measurement types

Presently, GEOSCOPE stations record in a continuous way :

  • ground velocity
  • mass position adapted to terrestrial tide studies,
  • air-pressure
  • temperature

This state of recording is the result of a slow evolution. So, from 1982 to 1987, GEOSCOPE stations record only ground velocity with a very long period output that is 1 point each 10 seconds. Then in 1988, other seismic channels are recorded :

- a long period output with 1 point per second.

- a broad-band output with 5 points per second.

- a very broad-band output with 20 or 30 points per second.

In 1997 are installed the first temperature sensors and the mass position channels adapted to terrestrial tide studies are being digitalized.

Last in 2000, air-pressure sensors are installed.

 

Sensor types

a - seismometers

GEOSCOPE was the first network which developped broad-band digital seismological stations, as soon as 1982 , using a new seismometer type, Streckeisen STS1, a leaf spring seismometer employing the force feedback system that extends the bandwith. This equipment characterized by a great dynamics and a wide frequency band suppressed the traditional boundary between short and long periods in seismology (Romanowicz et al, EOS Trans, 1984).

Streckeisen stopped making STS1 and sometimes we have to install STS2 seismometers. These last seismometers are less performent at long period and are often more noisy, that requires peculiar conditions when installing them.

 

b - digitizers

Since 2000, we have been equipping the stations with Quanterra digitizers, first serial number Q4120 (Q4126-6 channels or Q4128-8 channels) then presently serial number (Q330-6 ou Q330-HR). The Q330-HR we are installing since 2006, joins the Q4128 and Q330 qualities. It has got 3 26-bit channels, 3 24-bit channels et 4 16-bit channels, is cheaper and of use more simple.

 

Data format

Until year 2000, for most stations, the data were recorded in a format developped by the instrumentation team, then converted in the data center into a format adapted to a system of informations connected to a system of files, then distributed after a last conversion into the SEED format (Standard for the Exchange of Earthquake Data) adopted by FDSN.

These many conversions made too long the access to data. Consequently we had to think again about the acquisition system and the system of archieving and distributing data.

Presently, the digitizers installed in stations provide data in miniseed format which are archieved in GEOSCOPE Data Center in this format.

Metadata (information upon stations and their acquisition system) are recorded in a relational data base and can be distributed in dataless-SEED format.

With this system, we can quickly distribute data in SEED format (dataless+miniseed) with FDSN norms.