...
The HOAPS v4.0 precipitation retrieval was trained with precipitation rates retrieved from assimilated brightness temperatures in a 1D-Var scheme from ECMWF. The training data set is based on radiative transfer calculations as described in Bauer et al. (2006a, b). The data set contains one month (August 2004) of assimilated SSM/I brightness temperatures and the corresponding ECMWF 1D-Var retrieved precipitation values of the ECMWF model. The NOAA 0.25° daily Optimum Interpolation Sea Surface Temperature (OISST) (Reynolds et al., 2007; Reynolds, 2009) has been used as input for the processing of HOAPS v4.0.
...
Reynolds, R. W., Smith, T.M., Liu, C., Chelton, D. B., Casey, K. S., & Schlax, M. G. (2007). Daily High-Resolution-Blended Analyses for Sea Surface Temperature. J. Climate, 20, 5473–5496. http://doi.org/10.1175/2007JCLI1824.1Reynolds, R. W. (2009). What’s New in Version 2. OISST [Webpage]. http://www.ncdc.noaa.gov/sites/default/files/attachments/Reynolds2009_oisst_daily_v02r00_version2-features.pdf
Sanò, P., Casella, D., Mugnai, A., Schiavon, G., Smith, E. A., and Tripoli, G. J (2013). Transitioning from CRD to CDRD in bayesian retrieval of rainfall from satellite passive microwave measurements: Part 1. Algorithm description and testing, IEEE T. Geosci. Remote, 51(7), 4119–4143. https://doi.org/10.1109/TGRS.2012.2227332
...