def vel_disp(self, kwargs_mass, kwargs_light, kwargs_anisotropy, kwargs_apertur):
        """
        computes the averaged LOS velocity dispersion in the slit (convolved)

        :param kwargs_mass: mass model parameters (following lenstronomy lens model conventions)
        :param kwargs_light: deflector light parameters (following lenstronomy light model conventions)
        :param kwargs_anisotropy: anisotropy parameters, may vary according to anisotropy type chosen.
            We refer to the Anisotropy() class for details on the parameters.
        :param kwargs_apertur: Aperture parameters, may vary depending on aperture type chosen.
            We refer to the Aperture() class for details on the parameters.
        :return: integrated LOS velocity dispersion in units [km/s]
        """
        sigma2_R_sum = 0
        for i in range(0, self._num_sampling):
            sigma2_R = self.draw_one_sigma2(kwargs_mass, kwargs_light, kwargs_anisotropy, kwargs_apertur)
            sigma2_R_sum += sigma2_R
        sigma_s2_average = sigma2_R_sum / self._num_sampling
        # apply unit conversion from arc seconds and deflections to physical velocity disperison in (km/s)
        sigma_s2_average *= 2 * const.G  # correcting for integral prefactor
        return np.sqrt(sigma_s2_average/(const.arcsec**2 * self.cosmo.D_d**2 * const.Mpc))/1000.