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 developed 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 high-performing at long period and are often noisier, 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, data from most stations were recorded in a GEOSCOPE format developed by the instrumentation team and then converted into the FDSN SEED format (Standard for the Exchange of Earthquake Data) for distribution through the GEOSCOPE Data Center (operated until 2011).
These many conversions made too long the access to data. Consequently we had to think again about the acquisition system, archiving and distributing data services.
Currently, the digitizers installed in stations provide data in miniSEED format directly. The data is transmitted in real time to IPGP Data Center for distribution.
The metadata (station information, response instrument describing the acquisition system) is available in the FDSN StationXML format.