Hybrid Attention Transformers for Multi-Spectral Satellite Super-Resolution

Bridging Spatial Resolution and Radiometric Fidelity

Abstract

Spaceborne optical imaging missions, such as the European Space Agency's Copernicus Sentinel-2 constellation, provide vital multi-spectral observations worldwide, yet optical aperture diffraction limits native Ground Sampling Distance (GSD) to 10 m across visible and near-infrared (VNIR) bands. Traditional Single-Image Super-Resolution (SISR) algorithms designed for 8-bit photographic imagery introduce severe radiometric distortions that corrupt downstream biophysical canopy analyses. In this letter, we present HAT-Light, an edge-efficient continuous-scale Hybrid Attention Transformer engineered specifically for 4-channel (RGB+NIR), 16-bit Bottom-Of-Atmosphere (BOA) surface reflectance imagery. HAT-Light addresses the limitations of standard self-attention by integrating non-overlapping Window Multi-Head Self-Attention with Depthwise Convolutional Feed-Forward Networks (DW-FFN), effectively recovering translation-equivariant localized inductive biases essential for resolving fine agricultural field parcel boundaries and airport runway geometries. Arbitrary continuous magnification (s in [2.0, 4.0]) is enabled through harmonic sinusoidal Feature-wise Linear Modulation (FiLM) within a single checkpoint. Furthermore, we enforce physical radiance conservation through a composite multi-task loss suite that unites Smooth Charbonnier regression, 2D real Fourier transform (rFFT2) spectral alignment, directional Sobel edge penalties, and a numerically bounded Convex Cosine Spectral Angle Mapper (SAM) loss ensuring FP16 numerical stability. Evaluated across 600 curated Sentinel-2 test patches spanning five distinct biomes, HAT-Light establishes state-of-the-art accuracy (33.48 dB PSNR, 0.9048 SSIM, 1.37 deg SAM, and 1.89 ERGAS), outperforming Bicubic (+1.25 dB) and RCAN (+0.71 dB). Spatial edge transect profiling and agricultural NDVI correlation (R^2 = 0.898) confirm robust biophysical conservation. Under the Wald synthesis protocol on 100 authentic 2.5 m USGS NAIP aerial patches, HAT-Light achieves superior zero-shot transfer (0.8332 SSIM) at real-time edge throughput (78.7 FPS) on an edge GPU.