In the TU Wien soil moisture retrieval model the estimated standard deviation (ESD) is a measure for the different error types of the backscatter. This parameter is considered as a noise estimate, incorporating speckle and residual azimuthal effects, based on differences between fore- and after beam of the Advanced SCATterometer (ASCAT) on board the meteorological operational satellite METOP-A. However, for a robust estimate of the estimated standard deviation ESD, time series backscatter data of long period of time is necessary. This can be even up to several years. Thus in this work, the relationship of the current estimation of the standard deviation of the backscatter (ESD) with the standard deviation information (Kp) included in the Metop ASCAT Level 1b backscatter product is analyzed. For a comparison of ESD and Kp a new type of ESD is defined based on the radiometric resolution Kp, denoted as ESDKp. The elaborate analysis of the two ESD types reveals a nonlinear relation between the ESD and ESDKp, with much less impact of the azimuthal noise on the ESDKp. In particular, for arid regions with large azimuthal noise a substantial difference is observed, whereas for rain forests the values of the two ESD quantities are almost equal. As a contrast to the ESD, the value the ESDKp reaches steady value within a period of few weeks.