Being characterized by the self-adaption and high accuracy,
the
deep learning-based models have been widely applied in the 1D spectroscopy-related
field. However, the “black-box” operation and “end-to-end”
working style of the deep learning normally bring the low interpretability,
where a reliable visualization is highly demanded. Although there
are some well-developed visualization methods, such as Class Activation
Mapping (CAM) and Gradient-weighted Class Activation Mapping (Grad-CAM),
for the 2D image data, they cannot correctly reflect the weights of
the model when being applied to the 1D spectral data, where the importance
of position information is not considered. Here, aiming at the visualization
of Convolutional Neural Network-based models toward the qualitative
and quantitative analysis of 1D spectroscopy, we developed a novel
visualization algorithm (1D Grad-CAM) to more accurately display the
decision-making process of the CNN-based models. Different from the
classical Grad-CAM, with the removal of the gradient averaging (GAP)
and the ReLU operations, a significantly improved correlation between
the gradient and the spectral location and a more comprehensive spectral
feature capture were realized for 1D Grad-CAM. Furthermore, the introduction
of difference (purity or linearity) and feature contribute in the
CNN output in 1D Grad-CAM achieved a reliable evaluation of the qualitative
accuracy and quantitative precision of CNN-based models. Facing the
qualitative and adulteration quantitative analysis of vegetable oils
by the combination of Raman spectroscopy and ResNet, the visualization
by 1D Grad-CAM well reflected the origin of the high accuracy and
precision brought by ResNet. In general, 1D Grad-CAM provides a clear
vision about the judgment criterion of CNN and paves the way for CNN
to a broad application in the field of 1D spectroscopy.