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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _ir_calibrate(self, data):
 """Calibrate IR channels to BT."""

        fk1 = float(self["planck_fk1"])
        fk2 = float(self["planck_fk2"])
        bc1 = float(self["planck_bc1"])
        bc2 = float(self["planck_bc2"])

        res = (fk2 / xu.log(fk1 / data + 1) - bc1) / bc2
        res.attrs = data.attrs
        res.attrs['units'] = 'K'
        res.attrs['standard_name'] = 'toa_brightness_temperature'
        return res