Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2014, Vol. 11, No. 3, pp. 193-199
Detection of anomalous values of time series of vegetation indices
1 "Dubna" International University, Dubna, Russia
When compiling the seasonal series of vegetation indices, it is a challenge to identify and eliminate erroneous values. It is very important to distinguish false anomalies due to sustainable cloud cover from real ones caused by extreme weather conditions. This paper describes the methodology for detection of anomalous elements of vegetation indices time series, based on comparison of “expected” and registered values of measured parameter. Moreover, the classification of anomalies specific to spatial and temporal characteristics of their manifestation is proposed. Spatially, anomalies are divided into localized (L-anomalies) and migratory (M-anomalies). Depending on the mode of appearance, there are two types of anomalies: permanent anomalies (P-anomaly), having a stable source, and situational anomalies (S-anomaly), arising under certain circumstances. Examples of different types of anomalies are presented. Situational anomaly is considered as any deviation from the predicted value, which exceeds the specified threshold. To detect situational-migratory anomaly (SMA), apart from regular observations of probable territory of occurrence, it is necessary be able to recognize anomalies on a background of extreme seasonal conditions. Frequently it is not enough to detect the anomalies, we must also understand whether they are valid or erroneous. The calculation procedure of “expected” values and criteria for recognition of false anomalies are described. Recommendations for recovery measurement errors are provided.
Keywords: time series, vegetation indices, permanent anomalies, situational anomalies
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