  Multiband photometric transit observations or low-resolution spectroscopy
(spectro-photometry) are normally used to retrieve the broadband transmission
spectra of transiting exoplanets in order to assess the chemical composition of
their atmospheres. In this paper, we present an alternative approach for
recovering the broadband transmission spectra using chromatic Doppler
tomography based on physical modeling through the SOAP tool: CHOCOLATE
(CHrOmatiC line prOfiLe tomogrAphy TEchnique). To validate the method and
examine its performance, we use observational data recently obtained with the
ESPRESSO instrument to retrieve the transmission spectra of the archetypal hot
Jupiter HD 209458b. Our findings indicate that the recovered transmission
spectrum is in good agreement with the results presented in previous studies,
which used different methodologies to extract the spectrum, achieving similar
precision. We explored several atmospheric models and inferred from spectral
retrieval that a model containing H2O and NH3 is the preferred scenario. The
CHOCOLATE methodology is particularly interesting for future studies of
exoplanets around young and active stars or moderate to fast rotating stars,
considering SOAP's ability to model stellar active regions and the fact that
the rotational broadening of spectral lines favors its application.
Furthermore, CHOCOLATE will allow the broad transmission spectrum of a planet
to be retrieved using high signal-to-noise ratio, high-resolution spectroscopy
with the next generation of Extremely Large Telescopes (ELTs), where
low-resolution spectroscopy will not always be accessible.
