Nearly 400 Tycho-2 stars have been observed in a 720 square degree field in the direction of the North Galactic Pole with the high resolution echelle spectrograph ELODIE .
Absolute magnitudes , effective temperatures , gravities and metallicities have been estimated , as well as distances and 3D velocities .
Most of these stars are clump giants and span typical distances from 200 pc to 800 pc to the galactic mid-plane .
This new sample , free of any kinematical and metallicity bias , is used to investigate the vertical distribution of disk stars .
The old thin disk and thick disk populations are deconvolved from the velocity-metallicity distribution of the sample and their parameters are determined .
The thick disk is found to have a moderate rotational lag of -51 \pm 5 \mathrm { km s } ^ { -1 } with respect to the Sun with velocity ellipsoid ( \sigma _ { U } , \sigma _ { V } , \sigma _ { W } ) = ( 63 \pm 6 , 39 \pm 4 , 39 \pm 4 ) \mathrm { km s } ^ { % -1 } , mean metallicity of [ Fe/H ] = -0.48 \pm 0.05 and a high local normalization of 15 \pm 7 % .
Combining this NGP sample with a local sample of giant stars from the Hipparcos catalogue , the orientation of the velocity ellipsoid is investigated as a function of distance to the plane and metallicity .
We find no vertex deviation for old stars , consistent with an axisymmetric Galaxy .
Paper II is devoted to the dynamical analysis of the sample , puting new constraints on the vertical force perpendicular to the galactic plane and on the total mass density in the galactic plane .