Low resolution spectra of 23 stars towards the bulge globular clusters NGC 6528 and NGC 6553 are analysed .
Radial velocities and atmospheric parameters are derived in order to check their membership in the clusters .
Effective temperatures were obtained from photometric data for stars with T _ { eff } > 3800 K , whereas for cooler stars , they were derived from equivalent widths of TiO bands .
Calibrations of W ( TiO ) as a function of stellar parameters based on a grid of synthetic spectra are presented .
Metallicities were derived from a comparison of the observed spectra to a grid of synthetic spectra .
The sample comprises evolutionary stages from the Red Giant Branch to the Horizontal Branch , with parameters in the range 3200 \leq T _ { eff } \leq 5000 K and -0.5 \leq log g \leq 2.4 .
The mean metallicities obtained for NGC 6528 and NGC 6553 are [ Fe/H ] \approx -0.5 and -0.7 , in both cases with [ Mg/Fe ] = +0.3 ; assuming the same overabundance for the \alpha elements O , Mg , Si , S , Ca and Ti , this gives [ Z/Z _ { \odot } ] = -0.25 and -0.45 .
Membership verification by means of low resolution spectra is a crucial step in preparing targets for high resolution spectroscopy with 8m class telescopes .