  Long-range dependency modeling has been widely considered in modern deep
learning based semantic segmentation methods, especially those designed for
large-size remote sensing images, to compensate the intrinsic locality of
standard convolutions. However, in previous studies, the long-range dependency,
modeled with an attention mechanism or transformer model, has been based on
unsupervised learning, instead of explicit supervision from the objective
ground truth. In this paper, we propose a novel supervised long-range
correlation method for land-cover classification, called the supervised
long-range correlation network (SLCNet), which is shown to be superior to the
currently used unsupervised strategies. In SLCNet, pixels sharing the same
category are considered highly correlated and those having different categories
are less relevant, which can be easily supervised by the category consistency
information available in the ground truth semantic segmentation map. Under such
supervision, the recalibrated features are more consistent for pixels of the
same category and more discriminative for pixels of other categories,
regardless of their proximity. To complement the detailed information lacking
in the global long-range correlation, we introduce an auxiliary adaptive
receptive field feature extraction module, parallel to the long-range
correlation module in the encoder, to capture finely detailed feature
representations for multi-size objects in multi-scale remote sensing images. In
addition, we apply multi-scale side-output supervision and a hybrid loss
function as local and global constraints to further boost the segmentation
accuracy. Experiments were conducted on three remote sensing datasets. Compared
with the advanced segmentation methods from the computer vision, medicine, and
remote sensing communities, the SLCNet achieved a state-of-the-art performance
on all the datasets.
