  Although complex-valued (CV) neural networks have shown better classification
results compared to their real-valued (RV) counterparts for polarimetric
synthetic aperture radar (PolSAR) classification, the extension of pixel-level
RV networks to the complex domain has not yet thoroughly examined. This paper
presents a novel complex-valued deep fully convolutional neural network
(CV-FCN) designed for PolSAR image classification. Specifically, CV-FCN uses
PolSAR CV data that includes the phase information and utilizes the deep FCN
architecture that performs pixel-level labeling. It integrates the feature
extraction module and the classification module in a united framework.
Technically, for the particularity of PolSAR data, a dedicated complex-valued
weight initialization scheme is defined to initialize CV-FCN. It considers the
distribution of polarization data to conduct CV-FCN training from scratch in an
efficient and fast manner. CV-FCN employs a complex
downsampling-then-upsampling scheme to extract dense features. To enrich
discriminative information, multi-level CV features that retain more
polarization information are extracted via the complex downsampling scheme.
Then, a complex upsampling scheme is proposed to predict dense CV labeling. It
employs complex max-unpooling layers to greatly capture more spatial
information for better robustness to speckle noise. In addition, to achieve
faster convergence and obtain more precise classification results, a novel
average cross-entropy loss function is derived for CV-FCN optimization.
Experiments on real PolSAR datasets demonstrate that CV-FCN achieves better
classification performance than other state-of-art methods.
