Acquisition of 1second data in IPGP magnetic observatories

1
Acquisition of 1-second data in IPGP magnetic
observatories

• A. Chulliat, J. Savary, K. Telali, X. Lalanne

2
Motivations

• To provide data with the same characteristics as
  magnetometer chains (such as IMAGE, CANOPUS, GMC,
  etc.) for studying rapid variations of external
  origin.
• Ionospheric and magnetospheric electrical current
  systems
• ULF waves
• To be synchronized with magnetic satellites such
  as Ørsted, CHAMP and the upcoming Swarm.

• INTERMAGNET recommended the production on
  1-second data in 2003 (Dourbes meeting).
• Today more and more observatories are producing
  one-second data and INTERMAGNET is setting up the
  capability to distribute these data in quasi-real
  time.

3
Requirements

• Requirements 1-3 come from Jeff Loves survey
  (2005). Some users would like to have a better (1
  ms) time accuracy.
• Requirement 4 cannot be fully satisfied with
  existing fluxgate magnetometers. New, low-noise
  fluxgate magnetometers will have to be developed.

4
The IPGP 1-second system
5
Upgraded magnetometer

• The VM391 fluxgate magnetometer has been used
  for about 15 yrs in IPGP observatories. It is
• ring-core
• triaxial
• homocentric

IPGP VM391

• Upgrades made in 2008
• Changes in the analog part of the electronics
  (integrator, amplifiers)
• cutoff _at_ 2Hz
• 10 ms time accuracy
• Design and implementation of a new 24-bits ADC
• 10 pT resolution

6
Frequency response (amplitude)
2 Hz cut-off
X Y Z
dB
The frequency response is obtained by submitting
the magnetometer to a sinusoidal magnetic field
at a known frequency in a cylindrical coil.
Hz
7
Frequency response (phase)
2 Hz cut-off
lt 10 ms
X Y Z
ms
130 ms
Hz
8
Instrumental noise
Test of the magnetometer in a non-magnetic room
in Chambon la Forêt
Geomagnetic variations in CLF
10 pT/vHz _at_ 1 Hz
0.3 Hz
9
New data acquisition system

• A new data acquisition system, ENO3, has been
  developed and is now running in CLF.
• GPS synchronization
• Time delay correction
• Configuration via a web interface
• Data collection in ascii format
• Data transmission via the internet
• Control screen

10
Gaussian digital filter

• 15 points filter, centered on UT sec

• Requirements
• sampling frequency fs 5 Hz
• cutoff frequency fc 0.3 Hz
• smallest coefficient 0.01

where
0.3 Hz
11
Summary

• The upgraded IPGP VM391 magnetometer has the
  following characteristics
• 2 Hz cutoff frequency
• 10 ms time accuracy
• 10 pT resolution
• 10 pT/vHz _at_ 1 Hz noise
• A new, low-noise sensor will have to be developed
  if one wants to achieve a lower instrumental
  noise.
• The new ENO3 data acquisition system acquires
  data at 5 Hz and applies a Gaussian digital
  filter with cutoff at 0.3 Hz to produce 1-second
  data.
• The new 1-second system will be installed in
  other IPGP observatories and observatories in
  cooperation.