Comparison of NSCAT, ERS 2 active microwave instrument, special sensor microwave imager, and Carbon Interface Ocean Atmosphere buoy wind speed: Consequences for the air‐sea CO2exchange coefficient

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Abstract
Wind speedsUobtained using three different sensor types are compared to assess which might be most useful for calculating gas fluxes across the air‐sea interface.Uremotely sensed using scatterometer (ERS 2 and NASA scatterometer (NSCAT)) and microwave radiometer (special sensor microwave imager (SSM/I)) are compared with each other and withUmeasured in situ (Carbon Interface Ocean Atmosphere (CARIOCA) drifting buoy). The effect of different gridding schemes is also evaluated for the satellite data. Global comparisons for January 1997 indicate that 1° and monthly ERS 2Uare systematically 0.3 to 2 m s−1lower than NSCATUat mid and low latitudes. The NSCAT‐SSM/I comparisons are similar for the three SSM/Is. SSM/IUappear to be higher by 1 to 2 m s−1than NSCATUin the tropics and to be lower at high latitudes. When individual satellite measurements are collocated, ERS 2Uappear to be more coherent with NSCAT (rms of the difference equal to 0.8 m s−1) than SSM/IU(rms of the difference equal to 1.3 m s−1). However, when comparing 1° one‐week interpolated fields, NSCAT‐ERS 2 differences are more scattered than NSCAT‐SSM/I differences, because of the high ERS 2 undersampling. This flaw is attenuated when monthly interpolated 1° fields are compared. The CO2exchange coefficientsKdeduced from these remotely sensedUare compared. Longitudinal profiles of monthlyKare consistent within 0 to about 25% depending on the regions and on the instruments. Comparisons with in situ measurements in a region of very lowUin the eastern equatorial Pacific show excellent agreement between NSCAT and buoyU(bias of 0.3 m s−1) whereas ERS 2Uare underestimated by 1.3 m s−1and SSM/IUare overestimated by 0.7 m s−1on average.