Adélie Land, Base of Dumont d'Urville - (DRV)

Location

Instruments

Recording

INTERMAGNET

Key Dates

History

After 1950, the first magnetic measurements in the region of Terre  Adelie (Antarctica) were carried out in Port Martin, a base set up by the French polar expeditions (Missions Paul Emile Victor) in January 1950. The Port Martin magnetic observatory,created by P.N. Mayaud, was operated until February 1952 when the Port Martin base was destroyed by fire. In the austral summer 1956,the permanent Dumont d'Urville base was created.

During the IGY, the Dumont d'Urville observatory, situated on one of the coastal islands of the Pointe Geologie  archipelago, in Terre Adelie, was the only main observatory. A  temporary  observation station (the Charcot station) was set up 317 km away, to the south of Dumont d'Urville on the Antarctic inlandsis.

The magnetic observatory of Dumont d'Urville comprised three huts set up in the Petrels island, a few hundred metres away from  the residential quarters of the base. One of the huts housed the La Cour  magnetograph and another smaller hut housed the absolute pier.
An additional hut, equipped whith heating supply and telephone, was used to store apparatus and batteries and served as a shelter for observers during violent blizzards. Large local magnetic anomalies were detected, on the whole Petrel Island and especially around the absolute huts. These anomalies are due to outcropping veins of magnetite in the metamorphic, 1.7 milliard year old rocks. Therefore, it was known from the very opening of this observatory in April 1957, that the  mean level of the magnetic field measured in this region was not representative of the regional magnetic field. However, the variations in mean field values could be considered as being relevant indicators of secular variation Absolute measurements encountered major difficulties due to the low value of the horizontal component of the magnetic field and to magnetic disturbance, which is a common feature during the summer season. These difficulties were already known. P.N. Mayaud had faced them during 1951-1952 winters at Port Martin. Absolute measurements were made by mean of a Q.H.M., especially constructed for that purpose by P.A.Blum (IPGP), and by mean of a large-field B.M.Z. A La Cour magnetograph, oriented in the X-, Y- and the Z- directions recorded the variations of the  Earth's magnetic field. The observatory worked in this configuration until 1969.
In 1969 two photoelectric feed-back magnetometers (X and Y components) and an optical pumping magnetometer (Caesium vapor supplied by Varian) were set up in a new shelter heated at a constant temperature. A digital recording device on perforated tape was used to sample the X,Y and F elements at 1-minute intervals. This type of set-up ran until 1972 and absolute measurements continued to be made by means of traditional instruments (Polar Q.H.M., B.M.Z., completed by an ELSEC proton precession magnetometer).
In 1973 a VFO31 triaxial fluxgate variometer (X,Y and Z oriented) was installed at Dumont d'Urville. A low-power device for digital recording on magnetic tape was used (1973-1989). In 1990 a new digital data acquisition device was developed on the basis of a PC computer. For logistic reasons a new absolute hut was established in 1973 and the observatory references ware modified.
Since 1981 the EOPG (now EOST) portable magnetometer with fluxgate sensor for Earth's magnetic field component measurements has been used to made direct measurements of the intensity of horizontal components X and Y and of the vertical component Z. The measurements of total field F are made with an Overhauser magnetometer SM90R (since 1992).

Since January  20th 2009, new 1Hz Acquisitions Systems (M.A.R.Cell 1.0- Magnetic Acquisition and Recording Cell 1.0) were installed.

Absolute Measurements

The absolute pier (66.665 S, 140.007 E) has been the same since 1973. There are two jumps however:

• in 1982, due to the change of absolute instruments (the EOST portable magnetometer with fluxgate sensor for Earth's magnetic field component measurements replaced the old standards and a new emplacement of measurement point was adopted for X,Y,Z and F; local gradient caused a change of the observatory references).
• in 1995, due to the moving of the proton magnetometer sensor (local vertical gradient field produced a small modification of the F and Z observatory references).

Absolute measurements are performed on average every three days using the Declination-Inclination magnetometer D-I MAG 93. This D-I flux is based on a Zeiss 010B non-magnetic theodolite fitted with a single axis sensor mounted on the telescope. Due to strong inclination of the Earth's field, X and Y instead of D and I are measurement. Total field measurements are performed every minute with a proton Overhauser magnetometer SM90R.
The accuracy of the absolute determinations is estimated 2 nT for X,Y Z, and 0.2 nT for F.
 

Variometers

The fluxgate variometer (VFO31) and the proton Overhauser magnetometer (SM90R) recording total intensity F are placed in the variometer shelter heated at a constant temperature of 16 degrees Celsius. The triaxial variometer has a nominal output of 2.5 mV/nT and a dynamic of +/- 2000 nT. The long-term stability of the triaxial variometer is better than 1nT/month.
A fluxgate variometer (DMI suspended magnetomete model FGE) was put in December 1998 on an second pier close to the first fluxgate variometer VFO 31. This new variometer should be considered as a spare variometer, which allows us to fill in gaps of the VFO 31 records.

Accuracy of data

The adopted baseline values are calculated by spline smoothing. The uncertainty in the adopted baseline values, as well in the final 1-minute values, is estimated to be less than 2 nT for all elements.

Reference of the data

Detailed description of the instrumentation and method of data reduction are given in the annual bulletin of the Bureau Central de Magnetisme Terrestre (B.C.M.T., Paris).