Allan's-variance.md

@@ -4,6 +4,10 @@ Allan variance is a measure of the frequency stability of a signal over time, an
 
 The Allan variance is usually plotted as a function of the averaging time, and the resulting plot is called the Allan deviation. The Allan deviation plot allows for the analysis of the stability of the signal over different time scales.
 
+![images](uploads/4600ecc5a4929ed8b54f656a80d4659c/images.jpg)
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+On this picture we can see that the quartz clocks drift much faster than the GPS clocks.
+
 **There are three main regions that can be identified in an Allan deviation plot:**
 
 **-   Short-term stability:** This region corresponds to averaging times of less than 1 second. In this region, the Allan deviation is dominated by random noise and is inversely proportional to the square root of the averaging time.
@@ -13,3 +17,6 @@ The Allan variance is usually plotted as a function of the averaging time, and t
 **-   Long-term stability:** This region corresponds to averaging times greater than 1 day. In this region, the Allan deviation is dominated by other factors such as aging, temperature effects, and environmental disturbances.
 
 Allan variance is useful for measuring the stability and accuracy of a time and frequency signal over different time scales. It allows for the identification of different sources of error and instability, such as short-term noise, medium-term oscillator stability, and long-term environmental effects. Additionally, Allan variance can be used to compare the performance of different oscillators or clocks, and to determine the optimal averaging time for a specific application.
+
+Sources :
+Calero, D., & Fernandez, E., & Parés, E. (2016) Positioning performance of Chip-Scale Atomic Clock GNSS augmentation systems. [https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7849326](https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7849326)
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