Physical Principles of Earth Observation

Measuring is essential to characterize and explain processes in the Earth system, and a first step to assess, model and predict natural processes and human activities in and their impact on the Earth system. Electromagnetic, seismic and gravity potential-field observations inform us about a wide range of phenomena in the ocean, atmosphere, land surface, cryosphere and sub-surface. The measurements can be acquired from spaceborne, airborne, and surface-based sensors.

This programme core module aims to enable students i) to explain and apply the physical principles underlying the measurements, and ii) to assess what type of measurement could be used best to determine certain geophysical variables. For example, students will learn how electromagnetic theory allows to use the intensity of radar echoes to yield information about rain rate, soil moisture, ocean roughness, or the layering of the subsurface. Similarly, they will learn how potential field theory can be applied to quantify mass changes of, e.g., the ice sheets. Students will be able to weigh the advantages and disadvantages of, for example, microwave versus visible and near-infrared observations for monitoring the Earth surface, or between radar altimetry and spaceborne gravimetry to quantify ice loss (or gain) in polar regions.

• Review basics of electromagnetic (EM) waves (propagation, polarization, spectra, Doppler, etc.) and propagation effects (attenuation, refraction, dispersion, polarimetric effects)

• Optical-infrared scattering and propagation (different reflection types, albedo, effect of wavelength, BRDF, Radiative transfer modelling of optical EM waves).

• Physical principles and limitations of VNIR/SWIR sensing systems (photographic systems, LiDAR, spectral systems including TIR) in terms of spatial and spectral resolution, sensitivity, atmospheric disturbances and corrections.

• Microwave scattering and propagation (Rayleigh, Mie scattering, rough surface, volume scattering, clear air, radiative transfer modelling of microwave scattering in the atmosphere and at the land surface).

• Radiometry (Radiometric Quantities and Units, Blackbody Radiation, emissivity at different frequencies). Radiative transfer modelling in passive microwave remote sensing of the Earth’s atmosphere and surface.

• Physical principles and limitations of microwave sensing systems (radiometer, non-imaging radar, imaging radar, ground-penetrating radar) in terms of spatial and spectral resolution, sensitivity, atmospheric propagation effects and corrections, radar range equation

• Potential fields (gravity, magnetic and electric fields) and their relationship to physical properties of a medium (Gauss law and its applications, Newtonian/Magnetic Potential, Laplace equation and harmonic functions, representation of potential fields, spherical harmonics)

• Choose an approach for the observation and measurement of a geophysical variable.