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Table 1 Nomenclature used for “Methods for detecting and quantifying errors in sensor data”,“Methods for correcting errors in sensor data” and “Methods for detecting and correcting errors in sensor data” sections

From: Sensor data quality: a systematic review

Symbol

Description

\(x_i(t_j)\)

Measured data value \(x_i\) of sensor i at a specific point in time \(t_j\)

\({\hat{x}}\)

Estimated sensor data value

\(\vec {x}\)

Sensor data vector, where \(\vec {x} = \left( x_1,\ldots ,x_i,\ldots ,x_V\right)\) is a row vector obtained at the same point in time

t

Time in sensor data stream, e.g \(x_t\) is the observed sensor data value at time t

i

Column index \(i=1,\ldots ,V\)

j

Row index \(j=1,\ldots ,N\)

f

Feature

q

Size of moving window

N

Number of samples

V

Number of variables e.g. temperature, humidity, voltage

M

Number of sensor unit

F

Number of features

\(\mathbf{Z }\)

Sensor data stream in the form of a time series, \(\mathbf{Z } = \left( \dots ,\vec {x}_{t-1},\vec {x}_{t},\vec {x}_{t+1},\dots \right)\)

\(\mathbf{X }\)

Sensor data matrix where \(\mathbf{X } \in {\mathbb {R}}^{N\times V}\), \(\mathbf{X } = \left( \vec {x}_{1}, \ldots ,\vec {x}_{j},\dots ,\vec {x}_{N}\right)\)

  1. Depending on how the samples are obtained, the variables in sensor data vector \(\vec {x}\) might be produced by more than one sensor. For example, in environmental monitoring, the data may be produced by several sensors, each measuring one variable e.g. temperature and humidity. On the other hand, some variables are produced by one sensor alone, such as an accelerometer which produces readings for three variables i.e. the acceleration in the direction x, y, and z