What Is Land Surface?

Land surface is the interface between the solid or vegetated ground and the atmosphere, defined by the physical, thermal, and biochemical properties that govern the exchange of energy, water, and carbon between the terrestrial environment and the overlying air mass. It is not a simple geometric boundary but a complex, heterogeneous layer that includes bare soil, rock outcrops, vegetation canopies, snow and ice cover, inland water bodies, and urban built environments. The properties of this layer determine how solar radiation is absorbed and re-emitted, how precipitation partitions into runoff and infiltration, and how ecosystems interact with global climate systems.

Research into land surface spans geophysics, hydrology, ecology, and remote sensing engineering. IEEE contributions to the field center on sensor design, satellite data processing, and the signal and image processing methods used to extract quantitative surface parameters from spaceborne instruments.

Land Surface Characterization

Characterizing the land surface requires measuring several key biophysical parameters. Albedo, the fraction of incident solar radiation reflected by the surface, controls how much energy is absorbed and available for heating the air or evaporating water. Emissivity determines how efficiently the surface radiates thermal energy, and its accurate retrieval is essential for computing land surface temperature from satellite thermal-infrared measurements. Vegetation indices derived from multispectral imagery, such as the Normalized Difference Vegetation Index (NDVI), quantify photosynthetically active biomass and are produced from instruments including MODIS and the Visible Infrared Imaging Radiometer Suite (VIIRS). The NASA Land Processes Distributed Active Archive Center, operated jointly with the USGS, archives more than 14 petabytes of land surface products from these and other missions, making them freely accessible to the global research community.

Land Surface Energy Balance

The energy balance at the land surface links the incoming solar flux to the latent heat of evapotranspiration, the sensible heat warming the boundary layer, and the ground heat flux conducted into the soil. Accurate partitioning among these fluxes is central to weather prediction, hydrological modeling, and the parameterization of Earth system models. Field-based eddy covariance towers measure this exchange at point locations, while satellite remote sensing provides regional to global coverage. NOAA's Joint Polar Satellite System includes a VIIRS land surface temperature Environmental Data Record that reached validated maturity status in 2019, providing operational near-real-time coverage for North America and beyond. Soil moisture content, surface roughness, and the thermal inertia of the substrate all modulate how the energy balance shifts between seasons and land cover types.

Remote Sensing and Observation

Satellite platforms observe the land surface across a wide range of spectral and spatial scales. Passive optical sensors capture reflected solar radiation in visible, near-infrared, and shortwave-infrared bands, allowing land cover classification and vegetation monitoring. Thermal-infrared channels retrieve surface temperature and emissivity. Synthetic aperture radar (SAR) sensors penetrate cloud cover and vegetation canopies, providing surface roughness and soil moisture estimates under conditions where optical sensors are blind. The USGS surface energy balance estimation work demonstrates how aircraft-mounted optical systems can bridge the gap between ground-based tower measurements and coarser-resolution satellite products.

Applications

Land surface monitoring and characterization have applications in a range of fields, including:

• Numerical weather prediction and climate model parameterization
• Agricultural monitoring, crop yield forecasting, and drought assessment
• Urban heat island mapping and city planning
• Flood and wildfire risk assessment
• Carbon cycle and greenhouse gas inventory studies