South America Very Low Frequency NETwork (SAVNET)

The South America VLF Network (SAVNET) uses the properties of VLF wave propagation on long distances between a transmitter (TX) and a receiver (RX) in the Earth-Ionosphere Waveguide (EIW). The later is formed, on one hand, by the Earth surface, which is an electrical conductor, and on the other hand, by the low ionospheric D-region at ~ 70 km of altitude during diurnal conditions, and the E-region at ~ 90 km of altitude at night without the presence of solar radiation.

The characteristics of VLF propagating waves (amplitude and phase velocity) in the EIW will critically depend on the geometry of the EIW, the electrical conductivity of its borders, as well as of the geomagnetic field. All natural, or man-made, phenomena capable of changing these EIW properties will affect the characteristics of VLF propagation.

Scientific Objectives

SAVNET has two main objectives:
1. an indirect long-term monitoring of the solar radiation;
2. to provide a diagnostic to study the ionosphere above the South Atlantic Magnetic Anomaly (SAMA) region, during quiescent and geomagnetically disturbed periods.

Other objectives include:
1. ionospheric D-region properties study during transient perturbations like solar flares;
2. to diagnose extra-solar sources of ionospheric perturbations;
3. atmospheric and natural related phenomena producing ionospheric perturbations, like Sprites, TGFs, and Seismo-electromagnetic processes;
4. to provide experimental data sets to feed computational propagation codes in order to obtain daily templates of VLF waves properties on a given TX-RX propagation path;
5. to study the peculiar properties of the ionosphere at high (South) latitudes.

SAVNET Instrumentation

Each SAVNET base receiver is composed of two directional squared (3 m x 3 m) loop antennae, and an isotropic vertical (6 m) antenna. The sensor signals are amplified and transported to an A/D audio card. The waves characteristics are then provided by a Software Phase and Amplitude Logger (SoftPAL) computer code.

At this time SAVNET is composed of seven receiver bases, spreaded over the South American continent.

Five network sites will be chosen with respect to the South Atlantic Magnetic Anomaly region.

Financial Support:

Most of the SAVNET project is funded by the agency Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP). Additional funding is provided by Conselho Nacional de Pesquisas (CNPq), Centre National de la Recherche Scientifique (CNRS) and MACKPESQUISA.