# Presentation: 569155

## Acquisition of 1-second data in IPGP magnetic observatories

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

- XIIIth IAGA Workshop

- 16 June 2008

## 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.

- XIIIth IAGA Workshop

- 16 June 2008

## Requirements

- Requirements 1-3 come from Jeff Love’s 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.

| 1 | Resolution | 10 pT |  |
| --- | --- | --- | --- |
| 2 | Time accuracy | 10 ms | Centered on UT sec |
| 3 | Cut-off frequency | 0.3 to 0.5 Hz | Gaussian digital filter |
| 4 | Magnetometer noise | < Natural signal @ 0.3 Hz | Varies with latitude, typically 1 pT/sqrt(Hz) @1 Hz |

- XIIIth IAGA Workshop

- 16 June 2008

## The IPGP 1-second system

- XIIIth IAGA Workshop

- 16 June 2008

## Upgraded magnetometer

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

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

**IPGP VM391**

- XIIIth IAGA Workshop

- 16 June 2008

## Frequency response (amplitude)

**2 Hz cut-off**

- X
- Y
- Z

- Hz

- dB

- The frequency response is obtained by submitting the magnetometer to a sinusoidal magnetic field at a known frequency in a cylindrical coil.

- XIIIth IAGA Workshop

- 16 June 2008

## Frequency response (phase)

- Hz

- ms

**2 Hz cut-off**

- X
- Y
- Z

**< 10 ms**

**130 ms**

- XIIIth IAGA Workshop

- 16 June 2008

## Instrumental noise

- Test of the magnetometer in a non-magnetic room in Chambon la Forêt

**10 pT/****√Hz @ 1 Hz**

**Geomagnetic variations in CLF**

**0.3 Hz**

- XIIIth IAGA Workshop

- 16 June 2008

## 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

- XIIIth IAGA Workshop

- 16 June 2008

## Gaussian digital filter

**0.3 Hz**

- where

-  15 points filter, centered on UT sec

- Requirements:
-  sampling frequency fs = 5 Hz
-  cutoff frequency fc = 0.3 Hz
-  smallest coefficient = 0.01

- XIIIth IAGA Workshop

- 16 June 2008

## Summary

- The upgraded IPGP VM391 magnetometer has the following characteristics:
- 2 Hz cutoff frequency
- 10 ms time accuracy
- 10 pT resolution
- 10 pT/√Hz @ 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.

- XIIIth IAGA Workshop

- 16 June 2008