The influence of the detection direction on the quality of spectral data was not taken into account, which is catastrophic for some samples where the reflectivity direction was very different. To explore the directional characteristics of mixed pixels reflectivity, we used an ASD FieldSpec3 spectroradiometer to carry out multi-angle spectral measurement experiments in the laboratory, and the direction error model is established. As a result, the proportions of black area (PBA) and the observed azimuths (Φ) will affect the reflectivity of the mixed pixel in the visible light band. It is found that when the PBA is close to 0, the reflectivity distribution of mixed pixels is characterized by the reflected energy reflecting uniformly around the entire hemisphere space. When PBA is close to 1, there is a significant difference in the reflectivity of mixed pixels in 2π space. The direction error model better reflects the reflectivity changes caused by PBA and observed azimuth. The mean absolute error of the estimated reflectivity compared with the measured value is only 0.047. When the PBA is large, the estimation accuracy of the model is higher. When the PBA is small, and the observed azimuth is large, the accuracy of the model is slightly worse. The “two-block” mixed pixel is an ideal sample to satisfy the direction error model, while a dispersed “multi-block” mixed pixel is not applicable to the correction model. When conducting mixed pixel spectral measurement experiment, the influence of the detection azimuth on the spectral reflectivity should be fully considered, which is beneficial to improve the reliability of experiments on multi-angle spectral measurements of mixed pixels.

没有考虑检测方向对光谱数据质量的影响，这对于一些反射方向差异很大的样品来说是灾难性的。为探究混合像素反射率的方向特性，我们在实验室使用ASD FieldSpec3光谱仪进行多角度光谱测量实验，建立方向误差模型。因此，黑色区域（PBA）和观测方位角（Φ）的比例将影响可见光波段混合像素的反射率。发现当PBA接近于0时，混合像素的反射率分布特征是反射能量在整个半球空间均匀反射。当 PBA 接近 1 时，2π空间混合像素的反射率存在显着差异。方向误差模型较好地反映了PBA和观测方位引起的反射率变化。与实测值相比，估计反射率的平均绝对误差仅为 0.047。当 PBA 较大时，模型的估计精度较高。当PBA较小，观测方位角较大时，模型的精度稍差。“双块”混合像素是满足方向误差模型的理想样本，而分散的“多块”混合像素不适用于校正模型。在进行混合像素光谱测量实验时，应充分考虑探测方位对光谱反射率的影响，