The revolutionary approach to determining self-noise of the test seismometer by the use of two additional seismometers was presented by Sleeman et al (Bull Seismol Soc Am 96(1):258–271, 2006). Yet nowadays there are common situations where only two seismometers are installed side by side. This article thus outlines the various procedures that can be used in such situations. As it will be shown by examples, these procedures do not provide independent information unlike those given by three-seismometer procedures, however they still provide relevant data that can be used to assess the condition of the tested seismometers. Three equations are presented, that can be used in two-seismometer approach. The Eqs. 1 and 2 are already explained in the article (Tasič and Runovc in J Seismol 16:183–194. https://doi.org/10.1007/s10950-011-9257-4, 2012) The Eq. 3, which represents the “average self-noise”, differs from the equation “average self-noise” from the previously described article. Experimentally we found that the latter equation is not consistent with the results obtained for the “average self-noise” with the Sleeman procedure, while the equation for the “average self-noise” presented in this article is consistent with it. It is consistent in the frequency interval, where PSD of the seismic signal is at least 5 dB above the seismometers self-noises and it is very suitable for situations where two seismometers of the same type are compared between each other. This paper also presents an alternative three-seismometers approach. It is derived from the aforementioned Eq. 3. For this reason, at the frequency interval, where PSD of the seismic signal is at least 5 dB above the seismometers self-noises the output from this algorithm should be in accordance with the output from algorithm of Sleeman et al (Bull Seismol Soc Am 96(1):258–271, 2006). If there are deviations in certain frequency interval, this indicates some irregularities in the test itself. Under optimal measuring conditions, the Sleeman procedure is sufficient. However, if the test conditions are suboptimal, a comparison between the two procedures, where one contains division and the other does not, may be used to estimate the frequency range where the results are not reliable. Alternative equations, presented in this paper, are useful to discover unknown errors of the test system. The applicability of the equations is given by examples.

中文翻译：

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使用两个或三个并置地震仪估算“底噪PSD”：另一种方法

Sleeman等人（Bull Seismol Soc Am 96（1）：258-271，2006）提出了使用两个额外的地震仪来确定测试地震仪自噪声的革命性方法。但是如今，在常见情况下，只有两个地震仪并排安装。因此，本文概述了在这种情况下可以使用的各种过程。如示例所示，这些程序不像三地震仪程序所提供的那样提供独立的信息，但是它们仍然提供可用于评估被测地震仪状况的相关数据。提出了三个方程，可用于两个地震仪方法。等式 文章（Tasič和Runovc在J Seismol 16：183-194中进行了解释）已在文章中进行了解释。https：//doi.org/10.1007/s10950-011-9257-4，2012 表示“平均自噪声”的图3与前述文章的等式“平均自噪声”不同。从实验上我们发现，后面的方程与用Sleeman方法获得的“平均自噪声”的结果不一致，而本文中提出的“平均自噪声”的方程与此吻合。它在频率间隔中是一致的，其中地震信号的PSD比地震仪的自噪声至少高5 dB，并且非常适用于将两个相同类型的地震仪相互比较的情况。本文还提出了另一种三地震仪方法。它是从前面提到的公式得出的。3.因此，在频率间隔内 其中地震信号的PSD至少比地震仪自噪声高5 dB，该算法的输出应与Sleeman等人的算法的输出一致（Bull Seismol Soc Am 96（1）：258-271，2006 ）。如果某个频率间隔存在偏差，则表明测试本身存在一些不规则之处。在最佳测量条件下，Sleeman程序就足够了。但是，如果测试条件不是最佳的，则可以使用两个过程之间的比较（其中一个包含除法，另一个不包含除法）来估计结果不可靠的频率范围。本文提出的替代方程式对于发现测试系统的未知错误很有用。实例给出了方程的适用性。