def calibrate(self, data, dsid):
        """Calibrate the data."""
        tic = datetime.now()

        data15hdr = self.header['15_DATA_HEADER']
        calibration = dsid.calibration
        channel = dsid.name

        # even though all the channels may not be present in the file,
        # the header does have calibration coefficients for all the channels
        # hence, this channel index needs to refer to full channel list
        i = list(CHANNEL_NAMES.values()).index(channel)

        if calibration == 'counts':
            return data

        if calibration in ['radiance', 'reflectance', 'brightness_temperature']:
            # determine the required calibration coefficients to use
            # for the Level 1.5 Header
            if (self.calib_mode.upper() != 'GSICS' and self.calib_mode.upper() != 'NOMINAL'):
                raise NotImplementedError(
                    'Unknown Calibration mode : Please check')

            # NB GSICS doesn't have calibration coeffs for VIS channels
            if (self.calib_mode.upper() != 'GSICS' or channel in VIS_CHANNELS):
                coeffs = data15hdr[
                    'RadiometricProcessing']['Level15ImageCalibration']
                gain = coeffs['CalSlope'][i]
                offset = coeffs['CalOffset'][i]
            else:
                coeffs = data15hdr[
                    'RadiometricProcessing']['MPEFCalFeedback']
                gain = coeffs['GSICSCalCoeff'][i]
                offset = coeffs['GSICSOffsetCount'][i]
                offset = offset * gain
            res = self._convert_to_radiance(data, gain, offset)

        if calibration == 'reflectance':
            solar_irradiance = CALIB[self.platform_id][channel]["F"]
            res = self._vis_calibrate(res, solar_irradiance)

        elif calibration == 'brightness_temperature':
            cal_type = data15hdr['ImageDescription'][
                'Level15ImageProduction']['PlannedChanProcessing'][i]
            res = self._ir_calibrate(res, channel, cal_type)

        logger.debug("Calibration time " + str(datetime.now() - tic))
        return res