The AMBRE experiment onboard the ocean topography mapper JASON-3 aims at measuring
the spacecraft potential as well as auroral particle precipitation using two top-hat analyzers
for electrons and ions in the 20 eV–28 keV energy range. The JASON-3 spacecraft has a nearly
circular orbit at an altitude of 1,336 km with an inclination of 66°, at times probing the equatorward
part of the auroral oval in a nearly tangential manner upon leaving the outer radiation belt.

    AMBRE consists of two coupled top-hat analyzers, one for ions and the other for electrons in the 20 eV–28 keV 
    energy range. The field of view of both spectrometers is 180° × 6° centered on the zenith. The 180° plane 
    of view is divided into four anodes, the two central ones (sectors 2 and 3) looking at precipitating 
    particles while the two side ones (sectors 1 and 4) record nearly trapped particles (note that the angular 
    resolution of each anode is only ~35°). The geometries of both electron and ion analyzers are identical, 
    except that the electron analyzer has an entrance grid with a transparency of 10% (Sauvaud and Payan, 2017).

    The AMBRE spectrometers provide particle spectra with 128, 32, or 16 energy steps with a time resolution 
    that varies from 0.5 to 2 s. The geometrical factor of a single anode is 1.7 · 10−3 cm2.ster.eV/eV for ions 
    and 1.5 · 10−4 cm2.ster.eV/eV for electrons.