Spatial Resolution Enhancement of Microwave Radiometer Measurements: Methods and Applications

Dear Colleagues,

The microwave radiometer (MWR) is a passive remote sensing instrument; its measurements are useful for a broad range of applications, including land and ice studies, snow-cover classification, measurements of soil and plant moisture content, assessment of atmospheric moisture over land, analysis land surface temperature, and polar ice mapping.

MWRs can be designed to allow measurements at a given combination of frequency and polarization (single-channel MWRs). The Soil Moisture Active Passive (SMAP) radiometer is a single-channel MWR, as is the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS), which is part of the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission. Alternatively, they can be designed with multi-frequency and multi-polarization capabilities (multi-channel MWRs). The multi-channel MWR category includes instruments that can perform measurements at different channels (i.e., using different frequency/polarization combinations), e.g., the Special Sensor Microwave Imager (SSM/I), which covers four frequencies (ranging from 19.35 to 85.5 GHz) and seven channels (i.e., all the frequency channels, with the exception of the 23.235 GHz one, allow collecting measurements at both vertical (v) and horizontal (h) polarizations).

The MWR’s large-scale observations result in a very dense revisit time at the expense of a coarse spatial resolution when compared to optical or infrared (IR) sensors with similar receiving apertures. This coarse spatial resolution, although appropriate for climate studies, is a limiting factor when dealing with regional-scale applications. Hence, enhanced finer-resolution radiometer products have been proposed to exploit radiometer measurements in regional-scale applications and allow combining measurements collected at different frequencies (and, therefore, calling for different spatial resolutions) to provide better and more robust estimates of the geophysical parameter of interest. Those products can be generated using downscaling methods that can be roughly classified into two groups: data-fusion approaches and methods based on the inversion of the antenna pattern (i.e., antenna pattern deconvolution).

The aim of this Special Issue (SI) is to provide a unitary framework that includes the following:

• Leading-edge methods to downscale MWR measurements (statistically based methods, deterministic methods, neural network approaches, inversion of aperture-filtered measurements, data-fusion, multi-channel fusion, etc.)
• New earth observation (EO) applications based on the exploitation of resolution-enhanced MWR measurements obtained by exploiting either single-pass or multi-pass MWR measurements (soil moisture, sea ice maps, tropical cyclones, etc.)

Prof. Dr. Ferdinando Nunziata
Prof. Dr. Ran Tao
Guest Editors

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• microwave radiometry
• resolution enhancement
• downscaling
• inverse problems
• data fusion
• image reconstruction