Ground-based characterization of transiting exoplanets
Transmission spectroscopy is currently the most successful technique to explore the atmospheres of the exoplanets. We present several transmission spectra carried out with the 10.4m Gran Telescopio de Canarias (GTC) in La Palma (Spain). Two transits of Kepler-12b, two of WASP-36, and one of Qatar-1b observed with the OSIRIS spectrograph (Sánxhez et al. 2012). We describe the methods to extract the transmission spectra, together with the main challenges and techniques to model the systematic noises. We will present the final transmission spectra of these planets, which allow to constrain the atmospheric composition and the presence of clouds and/or hazes.