Remote Sensing of the Atmosphere

Core Idea

Atmospheric remote sensing measures the composition, structure, and dynamics of Earth's atmosphere from satellites. While surface remote sensing treats the atmosphere as an obstacle (to be corrected away), atmospheric remote sensing treats it as the target. Key measurements include atmospheric temperature and humidity profiles (from infrared and microwave sounders), cloud properties (from visible, infrared, and radar sensors), aerosol distribution (from multi-angle and polarimetric sensors), trace gas concentrations (from ultraviolet, visible, and infrared spectrometers), and precipitation (from radar and passive microwave). These measurements drive weather forecasting, climate monitoring, and air quality assessment.

Explainer

While most remote sensing courses focus on observing Earth's surface, the atmosphere is itself a complex, dynamic target observed by a dedicated constellation of satellites. Atmospheric remote sensing provides the data that drives weather forecasts, tracks air quality, monitors the ozone layer, and measures greenhouse gas concentrations for climate science.

Temperature and humidity profiling uses infrared and microwave sounders that measure thermal emission from the atmosphere at wavelengths where specific gases (primarily CO2 and H2O) absorb and emit. By selecting channels with different absorption strengths, sounders sample different atmospheric layers -- strong absorption channels see only the upper atmosphere, while weak absorption channels see down to the surface. This vertical sounding technique produces temperature and moisture profiles essential for initializing numerical weather prediction models.

Trace gas remote sensing exploits the spectral fingerprints of molecules. Each atmospheric gas absorbs at characteristic wavelengths: ozone in the ultraviolet, NO2 in the visible, CO and CH4 in the shortwave infrared, CO2 at 4.3 um and 15 um. Spectrometers with sufficient spectral resolution can measure the absorption depth and retrieve the column concentration of each gas. Instruments like TROPOMI, OMI, and OCO-2 have mapped air pollution, methane leaks, and carbon dioxide distribution with increasing spatial detail, informing both science and policy.

Precipitation estimation combines multiple sensor types. Passive microwave radiometers detect the scattering signature of ice particles in clouds. Cloud-profiling radar (on CloudSat and GPM) directly measures precipitation structure. Geostationary infrared imagery provides temporal context -- cold cloud tops indicate deep convection and heavy rain. The Global Precipitation Measurement (GPM) mission merges these observations to produce near-real-time global precipitation maps at 0.1-degree resolution every 30 minutes.