Close Window

Hofstra Univ.: "NEXRAD precipitation measurements combined with in-situ data to improve the accuracy of quickscat scatterometer wind estimates"

Final Report

Section 1: Project Objectives and Accomplishments

The context of this project is based on the utilization by the National Weather Service of a new satellite-based radar sensor whose purpose is to measure sea surface wind speed and direction with high spatial resolution. The NWS will benefit from timely use of this data in its marine and near coastal meteorological observation, warning and forecasting. This radar sensor is generally referred to as a scatterometer, and this particular satellite instrument in named "SeaWinds".

The overall objective of this COMET project was to develop a method to overcome the interfering of effect of rain on these satellite-based radar measurements by using the simultaneous NEXRAD precipitation measurements. The need is to improve the accuracy of sea surface wind estimates when rain is present within the satellite's field-of-view.

The near-term goals of this program were to develop the optimum software that could both read the NEXRAD Level III data products, and could also assimilate the scatterometer wind estimates from the SeaWinds data files, at locations within the NEXRAD observation range. This enabled the observation of the effect of rainrate (based on either the base reflectivity, composite reflectivity or vertically integrated liquid) on the accuracy of the scatterometer wind estimates (compared with nearby NDBC buoys).

A method has been developed using simultaneous, collocated SeaWinds, NEXRAD and NDBC buoy data to determine the dependence of the wind magnitude errors (differences between buoy winds and satellite sensor winds) on rain rate within the scatterometer radar illuminated cells (footprint). A major contribution to this effort has been the active collaboration of Dr. Mark Bourassa of the Center for Atmospheric-Ocean Prediction Studies of Florida State University. Their resources facilitated the collocation and acquisition of data from the NDBC buoy and QuikSCAT instruments. The NEXRAD data archive was utilized by the development of new software routines that provided easy access to 3 NEXRAD level III data products which are most relevant to the issues being studied here: base reflectivity, composite reflectivity and vertically integrated liquid. This collection of software created a merged data set for easy intercomparison among the scatterometer, buoy and NEXRAD wind and rain observations.

The relationships discovered by the analysis of these data have provided new and valuable knowledge that enables error estimates of the scatterometer winds to be made when rain is affecting the observation. This information can, in some cases, be used to correct these contaminated winds and thereby increase the value of this data for NWS applications. In addition, these initial findings will serve as a basis of a more extensive study to develop physical knowledge and techniques that will validate and/or correct the rain-contaminated wind vector estimates.

Section 2: Summary of University/NWS Exchanges

The first phase of our collaboration focused on developing the complimentary familiarity with the NEXRAD and QuikSCAT scatterometer measurement techniques and data sets. Dr. Weissman acquired knowledge of the NEXRAD system operation, data acquisition, the data archive characteristics and retrieval operations. Mr. Tongue (of the New York City NWS office) was introduced to the QuikSCAT satellite radar scatterometer; its measurement technique and data products. Numerous meetings were arranged to discuss the optimum utilization of the NEXRAD data products, and the validation of the output of the new software being used to read the NEXRAD archives.

A second phase involved our collaborator, Dr. Mark Bourassa, of FSU. The research facilities at FSU were able to provide Mr. Tongue and his colleagues within NWS several sets of near real-time scatterometer ocean wind vector. These were useful in augmenting the ocean surface observations normally used by NWS community to forecast coastal conditions. This new addition to NWS resources could be evaluated for its potential to improve forecasting in coastal regions. This activity also served as a training exercise for NWS personnel, and to give them the opportunity to learn the benefits of this new satellite system.

Section 3: Presentations

An invited presentation was made at the NEXRAD WSR-88D Workshop, at the NCDC in Asheville, NC, which took place December 2-3, 1999. This special meeting was convened to develop optimum plans to provide access to WSR-88D to meet research requirements. The title of the presentation was: Use of WSR-88D Data to Improve Accuracy of QuikSCAT Satellite Wind Measurements.

At the end of this one-year project, a paper was prepared and presented at the 2000 Spring Meeting of the American Geophysical Union in Washington, D.C.:
Weissman, D.E., M.A. Bourassa and J. Tongue: Relationship Between QuikSCAT Wind Speed Errors and Rain Rate Using Simultaneous, Collocated NEXRAD Data, 2000 Spring Meeting of the American Geophysical Union, Washington, D.C., May 30-June3 (Abstract: EOS, Transactions Vol. 81, No. 19, May 9, 2000, p. S282)

A presentation is planned for the National Weather Association Meeting, in October 2000:
Putting Advances in Remote Sensing to Operational Use: Understanding Scatterometer Data; Jeffrey S. Tongue, NOAA/NWS Forecast Office, Upton, NY, David E. Weissman, Hofstra University, Hempstead, NY and Mark A. Bourassa, COAPS, Florida State University, Tallahasse, FL.

Section 4: Summary of Benefits and Problems Encountered

Hofstra University gained from this collaborative project because a current research program, supported by the National Aeronautics and Space Administration to study the application of the QuikSCAT scatterometer, will benefit from having improved measurements of the sea surface radar cross section in the presence of rain. This project will be expanded with an additional inquiry into the physical processes that occur as the radar beam passes through a rain layer and interacts with the roughened surface, wherein the rain data can now be extracted from NEXRAD base and composite reflectivity files. .

A senior Electrical Engineering student was able to study the NEXRAD system and analyze a sample of NEXRAD base reflectivity data as a topic for this Honors thesis, in the Spring 1999 semester.