为了测算中分辨率光谱成像仪在轨调制传递函数(MTF)，提出了一种基于图像中非理想阶跃目标的处理方法。利用仅一侧具有较好均匀性的目标，在线扩散函数(LSF)的对称性假设下，实施基于阶跃响应思想的测算方法。与传统的阶跃边缘法相比，该方法得到的结果与中分辨率光谱成像仪获得的结果一致。将其应用在中分辨率光谱成像仪的指标考核中，得到的半峰全宽(FWHM)与传统处理方法仅相差0.03 pixel，奈奎斯特频率处的MTF值也仅相差0.02，验证了本文方法的有效性。该方法所利用的目标在中分辨率光谱成像仪遥感图像中极为常见，因而普适性更好。

In order to measure the on-orbit modulation transfer function (MTF) of medium resolution spectral imagers, an approach based on non-ideal step targets is proposed. By using targets with only one uniform side, the proposed method based on the step response is carried on the assumption that the line spread function (LSF) is symmetric. Compared with the traditional step edge method, this method achieves uniform results from the same target captured by a medium resolution spectral imager. The full width at half maximum (FWHM) derived by the proposed method differs from the traditional methods by only 0.03 pixel and the difference of the MTF value at the Nyquist frequency is only 0.02, which verifies the effectiveness of the proposed method. Since the using targets are very common in remote sensing images captured by medium resolution spectral imagers, the proposed method can be applied to more cases than the traditional approaches.