Improving QuikSCAT Winds in Tropical Cyclones

Hurricane Ike H*Wind Analysis
We support validation of surface winds through the use of the AOML/HRD H*Wind System. Shown above is a surface wind representation of Hurricane Ike (2008). This analysis was created from hurricane reconaissance, buoy, and satellite winds.

Summary

One of the many difficulties with forecasting tropical cyclone intensification and track is obtaining an accurate representation of the current wind field. Without knowledge of the storm's strength and structure, there will be higher error in computer model, and thus human, forecasts.

Recent advances in remote sensing (the measurement of environmental variables from a remote location) has led to the ability to measure surface wind speed and direction over oceans from satellites. The SeaWinds scatterometer (on board QuikSCAT) is an active instrument that sends a pulse of microwave radiation down to the ocean surface. The pulse backscatters off of capillary (wavelength ~ 1cm) waves on the ocean surface. These surface waves vary quite nicely with the surface wind stress, which is in turn a function of the surface wind speed and ocean currents. SeaWinds measures the amount of "power" returned by the ocean surface - more power generally means a rouger ocean surface and thus higher wind speeds. In addition, wind direction can be determined by measuring the polarization of the return beam from multiple azimuth angles.

Since tropical cyclones spend most of their time over the ocean (where surface observations are few and far between), it is immediately obvious that QuikSCAT could be a valuable source of surface wind information. The satellite retrieves surface wind speed and direction, and covers about 95% of the Earth's surface each day.

However, there is one very large obstable - rain. Rain contaminates the radiative beam in three ways: attenuation, enhanced backscatter from the drops, and enhanced backscatter from rain splashing on the surface. The relationships and impacts between these are complicated and nearly impossible to isolate. They vary according to the intensity of rain and the "true" surface wind speed (which is what you are trying to measure in the first place!). In tropical cyclones, where rain rates can reach incredible levels, QuikSCAT wind retrievals are inaccurate at best and worthless in the worst cases.

This project, in collaboration with the Central Florida Remote Sensing Lab (CFRSL), seeks to improve QuikSCAT wind retrievals in tropical cyclones. A new algorithm developed by Pete Laupattarakasem at UCF has been tested against H*Wind surface wind analyses. H*Wind incorporates all surface observations near the tropical cyclone in both space and time and performs an objective analysis to produce a gridded 6 km wind field. Pete has shown significant improvement in QuikSCAT wind wind retrievals when the algorithm is applied.

In June 2010, UNC Asheville was awarded a sub-contract with UCF to continue this important work.

Related Links:

Related Journal Articles:

  • Alsweiss, S., R. Hanna, P. Laupattarakasem, W.L. Jones, C.C. Hennon, and R. Chen, 2014: A Non-MLE Approach for Satellite Scatterometer Wind Vector Retrievals in Tropical Cyclones. Remote Sensing,6, 4133-4148, doi:10.3390/rs6054133.

  • Laupattarakasem, P., W.L. Jones, C.C. Hennon, I.S. Adams, J.W. Johnson, P.G. Black, J.R. Allard, and A.R. Harless, 2010: Improved Ocean Vector Winds using SeaWinds Active/Passive Retrievals, IEEE Transactions on Geoscience and Remote Sensing, 48,1-15.

  • Adams, I.S., C.C. Hennon, W.L. Jones, and K. Ahmad, 2006: Evaluation of Hurricane Ocean Vector Winds from WindSat. IEEE Transactions on Geoscience and Remote Sensing, 44, No. 3, 656-667.

Related Conference Preprints:

  • Laupattarakasem, P., W.L. Jones, C.C. Hennon, J.R. Allard, A.R. Harless, and P.G. Black, 2008: Q-Winds satellite hurricane wind speed retrievals and H*Wind comparisons.28th Conf. on Hurricanes and Tropical Meteorology (Orlando FL), American Meteorological Society.

  • Adams, I., C.C. Hennon, W.L. Jones, and K. Ahmad, 2005: Hurricane wind vector measurements from WindSat polarimetric radiometer. IGARRS 2005, IEEE, New York, Vol. 6, pp. 4014-4017.

  • Jones, W.L., I.S. Adams, and C.C. Hennon, 2005: Hurricane wind vector measurements from WindSat polarimetric radiometer. Proceedings, 59th Interdepartmental Hurricane Conference, Jacksonville FL.

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