## 4 Carols Airborne Data Analysis
### CAROLS Results
#### 4.2.1.1 Ocean Measurements  
Figure 8 compares simulated and measured brightness temperatures acquired over the Gulf of Biscay. On the whole, in spite of the systematic bias between simulations and observations, there is a good agreement between the variations of the measured and simulated values of Ty. The roll and pitch movements of the aircraft allow a wide range of incidence angles to be explored.  
Large fluctuations observed in Figure 8 denote radio-frequency interference effects occurring on the side-antenna during circles and wing wags at large incidence angles, when the antenna was pointing towards the south-east, and on both antennas at the end of the flight when approaching the coast; a bias is observed between measurements and simulations, throughout all flights. Investigations after the flights revealed that the radiometer bandwidth was too large, and that a connector was imperfectly isolated. These flaws were corrected for the 2008 and 2009 flights.  
Circle flights allowed a wide range of azimuth angles to be explored. Figure 9 illustrates the azimuthal variation of the signal observed and simulated with both antennas, when the incidence angle is close to 15\({}^{\circ}\). By separating in the simulation each component of the scattered signal, we would check that most of the observed azimuthal variation is due to surface scattering of galactic noise. At these incidence angles, the region of the sky affecting the measurements includes the Cygnus A source and part of the Milky Way, leading to \(\sim\)0.5 K azimuthal variations in the scattered galactic signal (see Figure 9, bottom). Furthermore, the simulations show (Figure 9 top) that the 2 scale/DV2 model is consistent with the observations, whereas the second harmonic of Ty predicted by the SSA/Kudr. model appears to be too large.  
Figure 8: Measurements (8 ms average) recorded at the Y port (close to H-pol), by the nadir (top) and side (bottom) antennas on 24 September 2007. Incidence angles are indicated by the color coding. The simulated values of Ty are indicated by the black line.  
Figure 9: Top: Variations in Ty (1s averages) as observed (colored points), and simulated using the 2 scale/DV2 (black) and SSA/Kudr. (grey) models during three circular flights. The azimuth angle is color coded. Bottom: Modeled variations of scattered galactic noise. Left: nadir antenna on 24/09/07; wind speed of 8.3 m/s. Right: side antenna on 28/09/07; wind speed of 8.4 m/s. (a bias has been artificially added to the measurements, to facilitate visual interpretation).  
On 28 September 2007, the wind speed increased from 3 to 9 m/s, from east to west along latitude 45.5\({}^{\circ}\)N. A 1K east-west gradient of Ty was observed during the northern flight on 28 September. This was associated with a 6 m/s wind speed gradient and with a 0.5 pss salinity gradient between the longitudes 2.7\({}^{\circ}\)W and 4.7\({}^{\circ}\)W. Simulations with the 2-scale emissivity model and DV2 spectrum are consistent with the observed gradient (see Figure 10).  
In this particular case, close to the longitude 3.5\({}^{\circ}\)W, it can be seen that the STORM derived wind speeds were helpful in interpreting the observed variability; indeed, contrary to the QSCAT wind speeds, the STORM measurements were acquired at the same time as the CAROLS data, and have a better spatial resolution (about 6 km \(\times\) 4 km instead of 25 km \(\times\) 25 km for Quickscat).  
Figure 10: Variations in Ty (1 s averages) are observed (green) and simulated using either QSCAT wind speed values (red), or wind speed values derived from the STORM scatterometer (blue) on 28/11/07, along latitude 45.5\({}^{\circ}\)N. The low values observed at 3.7\({}^{\circ}\)W correspond to a change in direction of the aircraft.  
Figure 9: _Cont._