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Univ. of South Florida: "Using WSR-88D and ACTS for precipitable water estimates and improving rainfall estimates"

Final Report


1.1 Introduction

The University of South Florida (USF) operates a 30/20 GHz satellite terminal at its Tampa campus that receives signals from the Advanced Communications Technology Satellite (ACTS) as part of NASA's ACTS Propagation Program. Data available from this terminal's automatic collection facilities include both meteorological measurements, such as instantaneous rainfall, and atmospheric data derived from 20/27.5 GHz satellite beacon signal strength and radiometer sky temperature. Coverage of the terminal's slant path to the satellite is also provided by the NWS's WSR-88D radar at Ruskin, Florida, allowing time-concurrent measurements from both facilities.

This effort was conceived as a seed project for the cooperation of NWS and USF in areas of mutual interest. Particularly, the premise of this project was that the collaborative study of liquid and gaseous water in the atmosphere may lead to improvements in mesoscale forecasting and satellite communication and the results of this project largely confirm this.

The overall technical goals of the effort were (1) to validate models based on the radiosonde-based measurement of precipitable water vapor using USF attenuation and radiometric data; and (2) to improve rain rate and rainfall estimates via correlation of reflectivity data with USF attenuation, radiometer, and rain gage data. The corresponding project was designed to be a preliminary study of (1) the measurement of precipitable water vapor using USF attenuation and radiometric data, and (2) the correlation of reflectivity data with USF ACTS attenuation, radiometer, and rain gage data for improved rain rate estimates.

In pursuit of the second objective, we

In pursuit of the first objective, we collected radiosonde-derived precipitable water vapor and time-concurrent attenuation data for one month.

USF and NWS investigators jointly supervised a USF graduate student, with NWS supervising the extraction and interpretation of radar reflectivity and radiosonde data, and USF supervising the extraction of attenuation and sky temperature (radiometer) data and the data correlation efforts.

1.2 Accomplishments

The second component of the proposed work, the correlation of radar reflectivity and propagation attenuation, demonstrated that a strong correlation exists between the two phenomena. The results are significant: non-polarimetric radar reflectivity tracks satellite propagation attenuation and vice versa. The second component of the work was to assess the potential of estimating precipitable water vapor using radiometric data. Two related conclusions arise from the results. First, no correlation was found in our data; we believe the primary cause is the low values of attenuation due to water vapor relative to the attenuation due to water droplets in the 20/30 GHz band. Second, the definitive answer is not yet known, since innovations in radiometer technology and calibration could provide the needed accuracy at low levels of attenuation.


A MS student from USF worked closely with NWS counterparts at the facility in collection, extraction, and interpretation of several data products from the NWS WSR-88D radar. Several joint meetings were held both at USF and NWS.


E. E. Wolfe, "Correlation of Ka-Band Propagation Attenuation and S-Band Doppler Radar Reflectivity," M.S. Thesis, University of South Florida, 1997.

E. E. Wolfe, P. G. Flikkema, and R. E. Henning, "Correlation of S-Band Weather Radar Reflectivity and ACTS Propagation Data in Florida," Proc. Twenty-First NASA Propagation Experimenters Meeting (NAPEX XIX), El Segundo, CA, June 11--13, 1997.

E. E. Wolfe, P. G. Flikkema, R. E. Henning, and C. Paxton, "Estimation of Rain Attenuation on Satellite Links Using Non-Polarimetric Radar Reflectivity," in preparation for submission to IEEE Transactions on Antennas and Propagation.


4.1 University's Perspective

Interaction with our NWS counterparts on this project was extremely rewarding. In particular, a great deal was learned about the potential gains from sharing ideas both between organizations (university and NWS) and across disciplines (meteorology and electromagnetic propagation). The work resulted in one M.S. thesis, and follow-on work (currently with no external funding) is underway.

No problems were encountered.

4.2 NWS Perspective

Benefits ranged from initiating a relationship with the USF Electrical Engineering Department to finding fundamental relationships in WSR-88D radar reflectivity to ACTS attenuation. While concrete improvements in operational forecasting were not made, this study served to determine whether more detailed research should be undertaken that would lead to improvements in WSR-88D radar reflectivity measurements and real-time precipitable water measurements.

We found a correlation with the WSR-88D reflectivity data and ACTS attenuation, radiometer, and rain gage data. This correlation indicates the possibility of developing a system to determine drop size distribution (DSD) in real-time. DSD is an unknown part of the radar equation but changes in DSD are significant to measurement of reflectivity and rainfall. More development should be undertaken on this issue.

Estimation of precipitable water vapor using USF attenuation radiometric data was less successful. Although no correlation was found, changes in equipment and calibration may provide a means to induce the attenuation level above the noise level.

No problems were encountered and it has been a pleasure working with our USF colleagues.