SPyCer: Semi-Supervised Physics-Guided Contextual Attention for Near-Surface Air Temperature Estimation from Satellite Imagery

TL;DR

SPyCer is a semi-supervised physics-guided network that can leverage pixel information and physical modeling to guide the learning process through meaningful physical properties, designed for continuous estimation of NSAT by proxy using satellite imagery.

Abstract

Modern Earth observation relies on satellites to capture detailed surface properties. Yet, many phenomena that affect humans and ecosystems unfold in the atmosphere close to the surface. Near-ground sensors provide accurate measurements of certain environmental characteristics, such as near-surface air temperature (NSAT). However, they remain sparse and unevenly distributed, limiting their ability to provide continuous spatial measurements. To bridge this gap, we introduce SPyCer, a semi-supervised physics-guided network that can leverage pixel information and physical modeling to guide the learning process through meaningful physical properties. It is designed for continuous estimation of NSAT by proxy using satellite imagery. SPyCer frames NSAT prediction as a pixel-wise vision problem, where each near-ground sensor is projected onto satellite image coordinates and positioned at the center of a local image patch. The corresponding sensor pixel is supervised using both observed NSAT and physics-based constraints, while surrounding pixels contribute through physics-guided regularization derived from the surface energy balance and advection-diffusion-reaction partial differential equations. To capture the physical influence of neighboring pixels, SPyCer employs a multi-head attention guided by land cover characteristics and modulated with Gaussian distance weighting. Experiments on real-world datasets demonstrate that SPyCer produces spatially coherent and physically consistent NSAT estimates, outperforming existing baselines in terms of accuracy, generalization, and alignment with underlying physical processes.

Figures (6)

• Figure 1: Illustration of the sensing gap between satellite observations and near-ground conditions. Satellites capture surface properties, while NSAT, measured 2 meters above the ground, drives human comfort and environmental processes. Near-ground sensors provide accurate but sparse measurements, leaving most areas unsampled. SPyCer leverages the energy exchange between land surface and near-surface atmosphere to estimate continuous, physically consistent NSAT from sparse sensors and satellite imagery.
• Figure 2: Overview of SPyCer. For each near-ground sensor, a square patch of satellite-derived LST and auxiliary variables is extracted, representing the local spatial neighborhood. SPyCer predicts the NSAT at the central pixel while leveraging contextual information from neighboring pixels through a physics-informed semi-supervised strategy. Learnable spatial contextual weights quantify the physical relevance of each neighbor, which guide the total loss defined in \ref{['eq:totalloss_patch']}.
• Figure 3: Representation of the SEB. Net radiation, primarily from solar and atmospheric inputs, is partitioned into three flux components: sensible heat flux ($H$) transferring energy to the air, latent heat flux ($LE$) driving evapotranspiration, and ground heat flux ($G$) conducted into the soil.
• Figure 4: Qualitative comparison of NSAT estimates on 08 August 2025. Columns show IDW, GB, MLP, and SPyCer predictions, alongside the high-resolution satellite image for context. Rows correspond to (a) the full region, (b) a semi-urban corridor with a river, and (c) a major industrial zone. SPyCer accurately captures large-scale temperature patterns while resolving fine-scale variability, including cold regions, river features, and industrial hotspots, outperforming GB and MLP in spatial fidelity and local detail.
• Figure 5: Temporal evolution of NSAT estimates from SPyCer, MLP, and GB compared to ground-truth measurements at two randomly selected near-ground sensors from April to October 2025. SPyCer closely follows both the amplitude and timing of temperature variations, whereas MLP and GB overestimate during warm periods and fail to capture fine-scale fluctuations.