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The Radiometric Block models the transformation of the energy to the output digital number. It also models the errors that affect the radiometry of the instrument. The radiometric Block processing is divided into several steps :• Irradiance to photons conversionThe image in irradiance has to be converted to number of photons taking into account the photon energy of the band. The central wavelength of the band is used to convert irradiance to photons. • Photons to electrons conversionIdeally each photon reaching the detector element is converted in one electron. In practice however not all photons are converted to electrons. The Quantum Efficiency (QE) defines the conversion rate. This parameters varies with each spectral channel. • Electrons to Digital Numbers ConversionAt this stage, the image is in number of electrons with all detection effects already added. Though the electronics is complex, it can be modelled in three steps: Electrons to voltage conversion: It is the process of clocking out the electrons from the CCD detector elements, charge transmission and conversion into an analogue voltage.  Voltage Amplification: Amplification of the signal. Signal Digitalisation: Digitalisation to obtain digital counts.In addition, this Block adds electronic noise like quantization noise or dark current.The conversion between radiance and DN needs the following sensor parameters: integration time, quantum efficiency and variable high & low gains. The Radiometric Blocks includes the following radiometric noises:• Photonic noise• Photo response non-uniformity (PRNU)• Dark Current and Dark signal non-uniformity (DSNU)• Defective PixelsThe Radiometric Block may also include additional calculations for calibration.