A recent study published in the ISPRS Journal of Photogrammetry and Remote Sensing, describes a physics-based framework that maps global subsurface soil temperature profiles by harnessing the multi-overpass capabilities of China's Fengyun (FY) meteorological satellites. This work was led by Prof. ZHAO Tianjie from the Laboratory of Earth Observation for Water at the Aerospace Information Research Institute of the Chinese Academy of Sciences (AIRCAS). The study introduces the Diurnal Soil Thermal–Mapping Algorithm for Profiles (DST-MAP), which transforms instantaneous satellite observations into continuous, hourly soil temperature estimates at depths of 5, 10, 20, and 30 centimeters. This achievement marks a critical advance from single-surface snapshots to four-dimensional monitoring of the Earth's surface thermal activities, adding depth as a new dimension.
Soil temperature governs land-atmosphere energy exchange, carbon cycling, and agricultural productivity. Traditional thermal infrared (TIR) sensors are accurate but cannot see through clouds and they capture only the "skin" temperature of the land surface. Existing reanalysis products rely on model simulations rather than direct observations, leaving significant gaps in our understanding of subsurface thermal dynamics.
The solution lies in capturing the complete diurnal temperature cycle (DTC). China's Fengyun-3 (FY-3) series meteorological satellites provide a unique solution through their strategically distributed orbital constellation. Leveraging the Microwave Radiation Imagers (MWRI) aboard FY-3B (13:40 local overpass), FY-3C (22:15), and FY-3D (14:00), the research team exploited the synergistic coverage of morning, afternoon, and evening orbits. By fusing these microwave observations with MODIS thermal infrared data, a novel retrieval framework, the DST-MAP, reconstructs the diurnal cycle of soil temperature and further links it to subsurface thermal propagation processes, enabling the estimation of soil temperatures at multiple depths. This approach allows the estimation of soil temperatures at multiple depths, extending satellite temperature sensing from the land surface to the shallow soil profile
"Our study shows that satellite observations can do more than describe surface thermal conditions from a single snapshot," said Prof. Zhao. "By integrating microwave and thermal infrared measurements across the diurnal cycle, we are able to capture how heat propagates downward through the soil profile. This makes it possible to monitor not only the surface, but also the temporal evolution of subsurface thermal states.
The study reveals clear spatial and temporal patterns in global soil temperature dynamics. Surface layers respond most rapidly to solar forcing, while deeper soil layers show progressively delayed temperature peaks and reduced diurnal amplitudes, reflecting the effects of thermal inertia and heat diffusion within the soil. The resulting global maps also show strong geographic contrasts in the timing of daily maximum soil temperature and in the temporal evolution of soil thermal states across different latitudes, land cover types, and climatic regimes.
Notably, the study moves beyond conventional static mapping by demonstrating the time-varying behavior of soil temperature profiles. Rather than providing only a snapshot of thermal conditions, the new framework captures soil thermal processes from two complementary dimensions: temporal variation and vertical structure. This capability offers a more physically meaningful description of land surface processes and provides valuable support for land surface modeling, hydrological simulations, freeze–thaw monitoring, and the assessment of heatwaves and drought events.
Prof. Zhao emphasized, "This work demonstrates that China's Earth observation constellation can advance remote sensing beyond surface skin temperature measurements to the characterization of subsurface thermal processes. It also opens a new pathway for monitoring land thermal dynamics using multi-source satellite systems."
Global soil temperature profiles across diurnal cycles retrieved from FY-3/MWRI passive microwave and MODIS thermal infrared data. (Image by AIRCAS)
This research is supported by China's National Key R&D Program and the FY-3 Meteorological Satellite Engineering Project. The global soil temperature profile dataset (2011–2024) is now publicly available via the National Tibetan Plateau Data Center, providing free access to the scientific community worldwide.
Research News
China's Fengyun Satellites Enable Breakthrough in Mapping Underground Soil Temperatures Worldwide
A recent study published in the ISPRS Journal of Photogrammetry and Remote Sensing, describes a physics-based framework that maps global subsurface soil temperature profiles by harnessing the multi-overpass capabilities of China's Fengyun (FY) meteorological satellites. This work was led by Prof. ZHAO Tianjie from the Laboratory of Earth Observation for Water at the Aerospace Information Research Institute of the Chinese Academy of Sciences (AIRCAS). The study introduces the Diurnal Soil Thermal–Mapping Algorithm for Profiles (DST-MAP), which transforms instantaneous satellite observations into continuous, hourly soil temperature estimates at depths of 5, 10, 20, and 30 centimeters. This achievement marks a critical advance from single-surface snapshots to four-dimensional monitoring of the Earth's surface thermal activities, adding depth as a new dimension.
Soil temperature governs land-atmosphere energy exchange, carbon cycling, and agricultural productivity. Traditional thermal infrared (TIR) sensors are accurate but cannot see through clouds and they capture only the "skin" temperature of the land surface. Existing reanalysis products rely on model simulations rather than direct observations, leaving significant gaps in our understanding of subsurface thermal dynamics.
The solution lies in capturing the complete diurnal temperature cycle (DTC). China's Fengyun-3 (FY-3) series meteorological satellites provide a unique solution through their strategically distributed orbital constellation. Leveraging the Microwave Radiation Imagers (MWRI) aboard FY-3B (13:40 local overpass), FY-3C (22:15), and FY-3D (14:00), the research team exploited the synergistic coverage of morning, afternoon, and evening orbits. By fusing these microwave observations with MODIS thermal infrared data, a novel retrieval framework, the DST-MAP, reconstructs the diurnal cycle of soil temperature and further links it to subsurface thermal propagation processes, enabling the estimation of soil temperatures at multiple depths. This approach allows the estimation of soil temperatures at multiple depths, extending satellite temperature sensing from the land surface to the shallow soil profile
"Our study shows that satellite observations can do more than describe surface thermal conditions from a single snapshot," said Prof. Zhao. "By integrating microwave and thermal infrared measurements across the diurnal cycle, we are able to capture how heat propagates downward through the soil profile. This makes it possible to monitor not only the surface, but also the temporal evolution of subsurface thermal states.
The study reveals clear spatial and temporal patterns in global soil temperature dynamics. Surface layers respond most rapidly to solar forcing, while deeper soil layers show progressively delayed temperature peaks and reduced diurnal amplitudes, reflecting the effects of thermal inertia and heat diffusion within the soil. The resulting global maps also show strong geographic contrasts in the timing of daily maximum soil temperature and in the temporal evolution of soil thermal states across different latitudes, land cover types, and climatic regimes.
Notably, the study moves beyond conventional static mapping by demonstrating the time-varying behavior of soil temperature profiles. Rather than providing only a snapshot of thermal conditions, the new framework captures soil thermal processes from two complementary dimensions: temporal variation and vertical structure. This capability offers a more physically meaningful description of land surface processes and provides valuable support for land surface modeling, hydrological simulations, freeze–thaw monitoring, and the assessment of heatwaves and drought events.
Prof. Zhao emphasized, "This work demonstrates that China's Earth observation constellation can advance remote sensing beyond surface skin temperature measurements to the characterization of subsurface thermal processes. It also opens a new pathway for monitoring land thermal dynamics using multi-source satellite systems."
Global soil temperature profiles across diurnal cycles retrieved from FY-3/MWRI passive microwave and MODIS thermal infrared data. (Image by AIRCAS)
This research is supported by China's National Key R&D Program and the FY-3 Meteorological Satellite Engineering Project. The global soil temperature profile dataset (2011–2024) is now publicly available via the National Tibetan Plateau Data Center, providing free access to the scientific community worldwide.