Definition - What does Correlogram mean?
A correlogram, also known as Auto Correlation Function (ACF) plot, is a graphic way to demonstrate serial correlation in data that doesn't remain constant with time. A correlogram gives a fair idea of auto-correlation between data pairs at different time periods. It's used as a tool to check randomness in a data set which is done by computing auto-correlations for data values at different time lags.
The auto-correlations are near zero for any time lag separation if it is random but if not, one or more of the auto-correlations will be non-zero.
Trenchlesspedia explains Correlogram
Correlograms can be used by municipalities to make estimates regarding repair or replacement or up-gradation of water and waste water pipelines. Different trenchless methods are such as cured-in-place pipe (CIPP), sliplining and pipe bursting are available for the same. Correlograms are also used for forecasting sewage inflow into wastewater treatment plants and to determine annual variation in properties of concentrated sludge.
For example, to determine variations in properties of concentrated sludge, the two variables used are sludge concentration and sludge organic ratio of the concentrated sludge. It is observed in studies that these two variables undergo their own seasonal changes.
When these factors were studied on a correlogram it was observed that the variables change every 360-380 days period and the periodicity becomes less prominent with time.