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This letter introduces a new approach to characterize small-scale humidity variations using ground-based microwave radiometry. For that purpose, a microwave profiler routinely performed different scan patterns during its deployment at the Atmospheric Radiation Measurement mobile facility in the Black Forest, Germany. Individual azimuth scans at 30deg elevation revealed spatial variations in integrated water vapor (IWV) up to plusmn10%. Aircraft observations were used to evaluate the performance of the microwave observations by comparing derived humidity fields with IWV retrieved along individual directions of the microwave radiometer. Distinct humidity signals were reproduced by both observations. Residual uncertainties can be attributed to the temporal variations during the time it took the aircraft to cover the boundary layer and uncertainties in the interpolation. Long-term scanning observations will be further explored to investigate land-surface interaction and to characterize subgrid variability.