A research team from the Aerospace Information Research Institute (AIR) of the Chinese Academy of Sciences has developed a new framework to evaluate soil moisture stations’ spatial representativeness globally. Their study found that about 63% of existing soil moisture observation stations reliably reflect conditions at the satellite pixel scale.

This study, published in IEEE Transactions on Geoscience and Remote Sensing, provides valuable insights into the optimal deployment of soil moisture sites and the robust validation of satellite products.

Soil moisture is crucial for climate systems, hydrology, and agriculture. While passive microwave remote sensing is effective for large-scale monitoring, it often suffers from low spatial resolution. In contrast, ground-based stations provide accurate local measurements but struggle to represent broader satellite-scale conditions, complicating the validation process.

To address these issues, the research team used the Extended Triple Collocation (ETC) method to assess the correlation between ground station data and satellite-scale soil moisture measurements, thereby avoiding the need for additional field data.

The researchers evaluated the spatial representativeness of 322 soil moisture stations worldwide. They determined that stations with an ETC-R value above 0.7 are representative of satellite-scale conditions. The results showed that roughly 63% of the stations achieved good spatial representativeness.

Moreover, the research revealed that higher surface heterogeneity, influenced by environmental factors like soil texture, land cover, elevation, and vegetation, reduces a station’s representativeness, particularly in areas with diverse land cover types, which emerged as the most influential factor.

Additionally, the researchers introduced a new metric called “similar area ratio of the sites,” which assesses how well a station’s environmental characteristics match those of the surrounding area. This approach, confirmed through high-resolution (1 km) soil moisture data analysis, highlights the impact of surface heterogeneity on soil moisture variability and station representativeness.

This novel framework is adaptable for evaluating other environmental parameters, making it a valuable tool for improving remote sensing validation. The findings significantly enhance satellite-based soil moisture monitoring and lay the groundwork for better climate monitoring, agricultural planning, and water resource management.