De. Weissman et al., MEASUREMENTS OF OCEAN SURFACE STRESS USING AIRCRAFT SCATTEROMETERS, Journal of atmospheric and oceanic technology, 14(4), 1997, pp. 835-848
Scatterometer model functions that directly estimate friction velocity
have been developed and are being tested with radar and in situ data
acquired during the Surface Wave Dynamics Experiment (SWADE) of 1991.
K-u-band and C-band scatterometers were operated simultaneously for ex
tensive intervals for each of 10 days during SWADE. The model function
developed previously from the FASINEX experiment converts the K-u-ban
d normalized radar cross-section (NRCS) measurements into friction vel
ocity estimates. These are compared to in situ estimates of surface wi
nd stress and direction across a wide area both on and off the Gulf St
ream (for hourly intervals), which were determined from buoy and meteo
rological measurements during February and March 1991. This involved t
he combination of a local, specially derived wind field, with an ocean
wave model coupled through a sea-state-dependent drag coefficient. Th
e K-u-band estimates u magnitude are in excellent agreement with the
in situ values. The C-band scatterometer measurements were coincident
with the K-u-band NRCSs, whose u estimates are then used to calibrate
the C band. The results show the C-band NRCS dependence at 20 degrees
, 30 degrees, 40 degrees, and 50 degrees to be less sensitive to frict
ion velocity than the corresponding cases for K-u band. The goal is to
develop the capability of making friction velocity estimates (and sur
face stress) from radar cross-sectional data acquired by satellite sca
tterometers.