3-D Sharpened Cosine Similarity Operation for Hyperspectral Image Classification

Due to the advantage of high spectral resolution, hyperspectral imaging techniques have been extensively used in a variety of fields. Hyperspectral images (HSIs) classification is one of the fundamental tasks and attracts significant research interest. HSIs classification is pivotal as it facilitates precise identification of objects, providing invaluable insights for Earth observation tasks, such as resource management and land cover analysis. In existing studies, convolutional operations have been broadly applied for HSIs classification, especially 3-D convolution, which has shown its effectiveness in extracting spectral–spatial features from the raw HSIs. However, HSIs exhibit the characteristic of high dimensionality and pose challenges in extracting more discriminative features. In order to enhance the capability of capturing discriminative spectral–spatial features, in this article, a novel and effective 3-D sharpened cosine similarity (SCS) operation is proposed, serving as a replacement for conventional 3-D convolutional operation in HSIs classification and enhancing the classification accuracy. The 3-D SCS operation calculates and sharpens the cosine similarity between kernels and HSI input data. Based on the 3-D SCS operation, a 3-D SCS neural network is developed for HSIs classification tasks. To evaluate the effectiveness of 3-D SCS operation, experiments are conducted on three real-world HSIs datasets, including the University of Pavia, the University of Trento, and the University of Houston. Quantitative and qualitative experimental results illustrate that the SCS operation can effectively extract discriminative spectral-spatial features, achieving superior performance over the CNNs under the same model configuration.