Microwave radiometry of snow covered terrain and calibration of an interferometric radiometer

Remote sensing of the Earth using microwave radiometers is an important tool for the monitoring of diverse environmental processes from space. Passive microwave instruments are used, amongst other applications, for the monitoring of ocean processes, the properties of soil and vegetation, and different aspects of the Earth's cryosphere. Compared to optical instrumentation, passive microwaves provide the advantage of being largely insensitive to atmospheric and lighting conditions. However, the radiometers typically suffer from a poor spatial resolution, which makes the interpretation of observations of heterogeneous areas challenging. An important part in understanding passive microwave signatures of the Earth's surface is the development of emission models, linking the observations to the physical properties of the target. Advanced models can be further applied to account for the effects of varying vegetation and land cover in the observation. The first part of this thesis dissertation describes the development, validation and application of a radiative transfer based model for the simulation of microwave emission from snow covered terrain. The model is an improvement of an existing model published in literature, introducing the possibility to account for the vertical layering of snow and ice structures in the simulation. The modified model is verified against experimental observations from ground based and airborne radiometer instruments, and finally applied for the retrieval of snow cover parameters from space. Calibration of radiometer instruments is a prerequisite for reliable observations. Calibration of space-borne radiometers is particularly challenging due to the typically high sensitivity of instrumentation to changes in environmental conditions. In the second part of this dissertation, the calibration method for a novel type of radiometer instrument, the first interferometric radiometer using aperture synthesis in space, is presented. Specifically, on-ground characterization of the calibration subsystem of the instrument is described, including an analysis of the effects of the characterization errors on the final performance of the instrument.