The Demeter microsatellite and ground segment

The Demeter program is the first application of the Myriade microsatellite program conducted by the Cnes (French Space Agency) since 1997. The Myriade objective was to benefit from the miniaturization of the technologies to develop a product with a reduced size, weight and cost able to implement either scientific missions, demonstrators or operational applications in different areas: earth observation, astronomy, fundamental physics or telecommunications, within limited financial budget.The Demeter satellite was launched in end of June 2004, from Baikonour, aboard a Dnepr launcher, on a sun synchronous orbit at 710 km altitude. Its main scientific objectives are the detection and characterization of ionosphere electrical and magnetic disturbances in connection with a seismic activity.The scientific payload has been built by French scientific institutes (LPCE, CESR, CETP) involved in external and internal geophysics and by SSD/ESTEC (ESA). It is composed of several electrical and magnetic sensors, an ion spectrometer, an energetic particle analyzer and a Langmuir probe.The Demeter platform is designed in order to offer a high level of performances in terms of power, attitude and orbit control, data storage and transmission, flexibility. For example the large amount of scientific data is transmitted to the ground station with a high data rate telemetry link in X band.This paper describes the Demeter satellite and ground segment. It focuses on the specific design adaptations of the Myriade product for Demeter and it presents the preliminary in orbit platform performances.     

Spatial and temporal distribution of landlocked Galaxias maculatus and Galaxias platei (Pisces: Galaxiidae) in a lake in the South American Andes

Galaxiids are present in many of the Andean lakes in southern South America. We studied landlocked Galaxias maculatus (Jenyns) and Galaxias platei Steindachner populations in a deep oligotrophic lake (Lake Gutiérrez, Patagonia, Argentina). Their temporal and spatial distribution, intralacustrine movements (horizontal and vertical), and spawning periods were analysed using several sampling techniques (ichthyoplankton net, seine net, gill net, and baited benthic taps). We identified the early life stages of both species based on their morphology and otolith shape. The free embryos of both species migrate to the limnetic zone, where they coexist as larvae, facing the same food availability and probably the same predation risk. Each species then moves on to its own juvenile and adult habitat: the littoral and benthic zone for G. maculatus and only the deeper benthic zone for G. platei. Their adult habitats and part of their spawning periods partly overlap.