## 3 Remote Sensors at the SAS
### Geomagnetic sensor  
Ground-based geomagnetic observatories are intended to provide a time series of accurate measurements of the natural magnetic field vector in a particular location on the Earth's surface. The data from the worldwide network of observatories are used for several scientific and practical purposes, some examples being (i) the synthesis and updates of the global magnetic field models [1]; (ii) the study of the solar-terrestrial relationships and the Earth's space environment, framed in the modern discipline of Space Weather [2]; and (iii) the support for other types of geophysical studies in a more regional or even local framework, such as mineral exploration, plate tectonics studies [3], or risk mitigation [4]. The geomagnetic observatory at the SAS in Livingston Island participates in the global network of geomagnetic observatories [5]. It was deployed in December 1996 and it was given the three letter code LIV by the International Association of Geomagnetism and Aeronomy (IAGA). Data collection and management is driven by the EO institute. Although the Spanish station is manned only during summer season, roughly from November to February, the instruments are left recording during the whole year, which implies the equipment is unattended during more than 8 months per year. From 1996 to 2008 the SAS observatory consisted of three huts: one houses the absolute instrument, the so-called D/I fluxgate theodolite, which permits a manual measurement of the Declination and Inclination angles of the vector magnetic field in _absolute_ terms (for a discussion of the uncertainties made with this instrument see [6]). This instrument consists of a fluxgate magnetometer bar mounted on the telescope of a non-magnetic theodolite. A second hut houses a variometer of the type \(\delta D/\delta I\) vector magnetometer [7], which automatically measures the variations of the magnetic field vector once per minute. This instrument consists of two perpendicular pairs of Helmholtz coils, the polarization of which allows measuring the Declination and Inclination variations by means of a Proton magnetometer locatedat their center (see [8] for an assessment of this instrument). The Proton magnetometer, in turn, measures the total field intensity, F, when the coils are not polarized. Finally, the electronic system controlling this automatic instrument is placed in a third hut. From 2008 onward, a new variometer has been added up to the old instrumentation. The new magnetometer is a three-axis fluxgate, and allows automatically measuring the magnetic field variations from an analogue output, which is currently sampled at both, 1 and 0.1 Hz by the corresponding analog to digital converter (ADC). Once the raw observatory data are processed, the definitive data set is sent to the World Data Centres, where the worldwide scientific community can access them. This process may well take several months; however, for several scientific and practical purposes it is convenient to have real-time access to the data, especially for those unattended and/or remote observatories such as LIV. The INTErnational Real-time MAGnetic observatory NETwork (INTERMAGNET) provides means to access the data in near real-time through a satellite link. The data are thus packed and sent to the geostationary satellites, and afterwards collected by the so-called Geomagnetic Information Nodes (GINs), where the information is freely accessible. However, almost ten years of experience with satellite transmissions have shown us that the satellite link is not 100% reliable, and therefore it is suitable to have an alternative mean to retrieve the geomagnetic data. The skywave digital communication system between Antarctica and Spain designed within the research project between LA SALLE and the EO is intended to provide this backup/alternative to the satellite link. There are two major motivations to design a backup system by skywave.