Willard J. Pierson

NSCAT high-resolution surface wind measurements in Typhoon Violet

NASA scatterometer (NSCAT) measurements of the western Pacific Supertyphoon Violet are presented for revolutions 478 and 485 that occurred in September 1996. A tropical cyclone planetary boundary layer numerical model, which uses conventional meteorological and geostationary cloud data, is used to estimate the winds at 10-m elevation in the cyclone. These model winds are then compared with the winds inferred from the NSCAT backscatter data by means of a novel approach that allows a wind speed to be recovered from each individual backscatter cell. This spatial adaptive (wind vector) retrieval algorithm employs several unique steps. The backscatter values are first regrouped in terms of closest neighbors in sets of four. The maximum likelihood estimates of speed and direction are then used to obtain speeds and directions for each group. Since the cyclonic flow around the tropical cyclone is known, NSCAT wind direction alias selection is easily accomplished. The selected wind directions are then used to convert each individual backscatter value to a wind speed. The results are compared to the winds obtained from the tropical cyclone boundary layer model. The NSCAT project baseline geophysical model function, NSCAT 1, was found to yield wind speeds that were systematically too low, even after editing for suspected rain areas of the cyclone. A new geophysical model function was developed using conventional NSCAT data and airborne Ku band scatterometer measurements in an Atlantic hurricane. This new model uses the neural network method and yields substantially better agreement with the winds obtained from the boundary layer model according to the statistical tests that were used.

The winds of the comparison data set for the Seasat Gulf of Alaska experiment

The ship and data buoy winds used for comparison in the validation of Seasat-derived winds are described in terms of the time series of hourly wind observations from the buoys and in terms of the technique used to produce 20- and 30-min average winds from the ships. Sources of scatter in the comparison data are briefly reviewed.

Mesoscale and synoptic‐scale effects on the validation of NSCAT winds by means of data buoy reports

Consecutive 10-min reports by National Data Buoy Center buoys are analyzed so as to show the behavior of the anemometer for light and variable low wind speeds and for the mesoscale effects that remain in the 10-min averages for higher wind speeds. It is shown that the major contribution to the scatter in the comparison of NASA Scatterometer winds to data buoy winds is the result of the properties of the data buoy measurements. Calms, light winds and winds over 20 m s−1 still need additional study and further efforts at validation.

Winds Over the Ocean as Measured by the Scatterometer on SEASAT

The SEASAT SCATTEROMETER (SASS) measured the winds on a global scale over the ocean from June 1978 through October 1978 for a total of nearly 100 days. The concepts that were used had a long period of development starting in 1967.

The Potential Impact of Seasat-A on the Study of the Planetary Boundary Layer Over the Ocean

At an IUGG-IUTAM Symposium in 1966 at Kyoto, Japan, a brief paper by me made some general comments on our inadequate understanding and knowledge of the planetary boundary layer over the oceans.* The possibility that earth orbiting spacecraft could measure waves over the ocean and provide data from which very high quality synoptic surface weather maps and wind fields could be determined was described.