SOCRATES HCR ocean scan calibration

Based on the work of Li et al. (2005) we use the backscattering properties of the ocean surface as a calibration reference. Results from Li et al. (2005) indicate that near a 10° incidence angle, the normalized ocean surface radar cross section σ0 is insensitive to surface wind conditions and has a value of ~6 dB. To make use of these results several ocean-scan calibration (OSC) events were performed during SOCRATES which each consisted of ~4 minutes of cross-track scanning from 20° to -20° off-nadir. We use

to calculate the normalized radar cross section bias σ0 bias of HCR, where σ0 theory is 6 dB, Z is the measured reflectivity, c is the speed of light, τ is the pulse width, |K|2 is the radar dielectric factor, λ is the signal wavelength, la0 is the nadir atmospheric attenuation, and Θ is the elevation angle.


Using data of 10° plus/minus 0.3° incidence angle, the mean bias for all OSC events was 2.1 dB which was then added to the whole data set.

The atmospheric attenuation was calculated using the methods of Liebe (1985) and the ITU Recommendation (2013). The results of both methods differed by ~0.2 dB and were averaged in the bias calculation.