SNO Method:

We look for paired footprint between Jason-2 and other satellites (SARAL, EnviSAT, AMSU etc) in a distance of 20 km and in a time of 3 minutes. By quality control (remove data on different surface boundaries, range exceeding three times of standard deviation etc) and averaging over all foot prints, time series can be obtained for both Jason-2 and other satellites on different channels.

The left figure displays all the SNOs between Jason-2 and EnviSAT during 07/2008-04/2012. The right pannel shows that with SARAL during 03/2013-03/2014.

Coldest Ocean Method:

The coldest ocean method looks at the histograms of all the brightness temperatures measured over ocean surface and determines the coldest brightness temperature by extrapolating the fitted line in the range of 0.5%-1% to 0% (Scharroo et al. 2004).

The left panel shows the histgram of BT of Jason-2 AMR on 23.8 GHz on cycle 201. The mid pannel is the cumulative curve and the right pannel shows the details of the regression using the cumulative curve.