Performance of Airborne Microwave Remote Sensors in Hurricane Allen

In August 1980 two remote sensing instruments from the NASA Langley Research Center were flown through Hurricane Allen. These were the C-band Stepped Frequency Microwave Radiometer (SFMR) and the Ku-band Airborne Microwave Scatterometer (AMSCAT), carried on a NOAA aircraft at 3000 m altitude. An SFMR sea surface wind speed is calculated from the increase in antenna brightness temperature above the estimated calm-sea value, and an SFMR rain rate is calculated from the difference in antenna temperature measured at two frequencies. In the absence of severe beam attenuation caused by rain, an AMSCAT surface wind vector is determined from the sea´s normalized radar cross section measured at several azimuths. Comparison wind data were provided with the INS on board the aircraft at 3000 m and on a second, lower altitude, aircraft. The analysis shows that, once the rain free periods are selected with the SFMR data, the AMSCAT produces well behaved and consistent wind vectors.