Ralf Kohley Gaia Calibration Engineer in the Science Development Division at ESAC I have studied Physics at the University of Bonn, Germany followed by a Ph.D in Astronomy from the same University. My reasearch topics concentrated on instrumentation and imaging detectors for astronomy, where I am active since the early nineties. During the last nine years I have been working as detectors specialist for the GTC project in Tenerife (10m segmented mirror telescope). I have been responsible for all imaging detector systems of the telescope including acquisition and guiding, adaptive optics and scientific instrumentation, mostly optical, based on CCDs but also SWIR and mid-IR detector systems. Throughout my career I have been involved in building three facility instruments, the last a general purpose imager and low resolution spectrograph working in the visible wavelength range (ELMER). Further involvements include the development of a novel L3CCD for AO and planet finding applications (OPTICON JRA2), IMaX (solar magnetic field imager), FastCam (high spatial and temporal resolution imager in the visible), FRIDA (NIR integral field spectrograph and imager for AO) and SIDE (visible and NIR fiber-fed medium-resolution spectrograph for MOS and integral field spectroscopy). Two months ago I have joined the Gaia team to work on calibration tasks for the instruments, FPA and data processing. Apart from the fundamental understanding of instrumental parameters in astronomical data, my research interests are novel imaging detectors from the UV to mid-IR, instrumentation technology and observing techniques.