School of Meteorology (Defense)

Evaluation of a Microwave Radiometer Thermodynamic Retrieval Algorithm

Stephen G. Castleberry
OU School of Meteorology

24 July 2014, 2:00 PM

National Weather Center, Room 5820
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

With an ever-growing need to improve the understanding and prediction of how mesoscale and smaller weather features initiate and evolve, there is a strong motivation for higher resolution thermodynamic profiling of temperature and humidity on smaller spatial and temporal scales than can be provided by current observational strategies. For example, while radiosondes do provide accurate thermodynamic profile information at synoptic-scale (generally twice per day) timing, the infrequency of these observations make it possible to potentially miss the onset and evolution of meteorological events that occur on much smaller time scales. Further, while satellite-based remote sensing and aircraft observations produce accurate observations on the free troposphere, the need for observations of thermodynamics in the boundary layer and lower troposphere is a critical gap in our measurement strategy.
One potential way to fill this gap is to utilize thermodynamic profiling from a ground-based microwave radiometer (MWR). The MWR measures downwelling spectral radiance from the atmosphere in the microwave portion of the spectrum (~ 20 to 60 GHz), which can be used in an iterative algorithm to retrieve vertical temperature and humidity profiles within the lowest 2-4 km of the atmosphere (within and just above the boundary layer) at temporal resolutions on the order of 5 minutes. This research focuses on using a dataset from a Radiometrics MP-3000A MWR, which was operated on the rooftop of the National Weather Center in Norman, OK, from approximately October 2011 through June 2013. An algorithm was implemented, the error characteristics evaluated, and several case studies were examined. This project’s overall aim is to eventually use this algorithm to help supplement existing profiling systems and radiosonde observations to improve current boundary layer studies and improve the evaluation of pre-convective environments and weather forecasting.
Overall, this project confirmed, as in the literature and past studies, that it is indeed possible to employ downwelling spectral radiance observations from ground-based profilers such as the MWR to retrieve vertical profiles of temperature and
humidity in the lower atmosphere. The technique examined shows potential for providing an additional method for higher temporal resolution thermodynamic profiling within and just above the boundary layer, despite several calibration / bias issues with the MWR data and despite various errors associated with the radiative transfer algorithm. Further, it was found that when examined in a time series, the retrieved profiles do exhibit the ability to detect relatively small scale meteorological features that otherwise could be missed by traditional profiling techniques alone, although more work is still needed to make the technique more accurate.

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School of Meteorology (Defense) Seminar Series website