def integral(self, bandname):
        """Calculate the integral of the spectral response function for each
        detector.
        """
        intg = {}
        for det in self.rsr[bandname].keys():
            wvl = self.rsr[bandname][det]['wavelength']
            resp = self.rsr[bandname][det]['response']
            intg[det] = np.trapz(resp, wvl)
        return intg