TY  - JOUR
A1  - Schneider, Johannes
A1  - Wenig, Phillip
A1  - Papenbrock, Thorsten
T1  - Distributed detection of sequential anomalies in univariate time series
JF  - The VLDB journal : the international journal on very large data bases
N2  - The automated detection of sequential anomalies in time series is an essential task for many applications, such as the monitoring of technical systems, fraud detection in high-frequency trading, or the early detection of disease symptoms. All these applications require the detection to find all sequential anomalies possibly fast on potentially very large time series. In other words, the detection needs to be effective, efficient and scalable w.r.t. the input size. Series2Graph is an effective solution based on graph embeddings that are robust against re-occurring anomalies and can discover sequential anomalies of arbitrary length and works without training data. Yet, Series2Graph is no t scalable due to its single-threaded approach; it cannot, in particular, process arbitrarily large sequences due to the memory constraints of a single machine. In this paper, we propose our distributed anomaly detection system, short DADS, which is an efficient and scalable adaptation of Series2Graph. Based on the actor programming model, DADS distributes the input time sequence, intermediate state and the computation to all processors of a cluster in a way that minimizes communication costs and synchronization barriers. Our evaluation shows that DADS is orders of magnitude faster than S2G, scales almost linearly with the number of processors in the cluster and can process much larger input sequences due to its scale-out property.
KW  - Distributed programming
KW  - Sequential anomaly
KW  - Actor model
KW  - Data mining
KW  - Time series
Y1  - 2021
U6  - https://doi.org/10.1007/s00778-021-00657-6
SN  - 1066-8888
SN  - 0949-877X
VL  - 30
IS  - 4
SP  - 579
EP  - 602
PB  - Springer
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Böckmann, Christine
A1  - Wandinger, Ulla
A1  - Ansmann, Albert
A1  - Bösenberg, Jens
A1  - Amiridis, Vassilis
A1  - Boselli, Antonella
A1  - Delaval, Arnaud
A1  - De Tomasi, Ferdinando de
A1  - Frioud, Max
A1  - Grigorov, Ivan Videnov
A1  - Hagard, Arne
A1  - Horvat, Matej
A1  - Iarlori, Marco
A1  - Komguem, Leonce
A1  - Kreipl, Stephan
A1  - Larchevque, Gilles
A1  - Matthias, Volker
A1  - Papayannis, Alexandros
A1  - Pappalardo, GGelsomina
A1  - Rocadenbosch, Francesc
A1  - Rodrigues, Jose António
A1  - Schneider, Johannes
A1  - Shcherbakov, Valery
A1  - Wiegner, Matthias
T1  - Aerosol lidar intercomparison in the framework of the EARLINET project : 2. Aerosol backscatter algorithms
N2  - An intercomparison of aerosol backscatter lidar algorithms was performed in 2001 within the framework of the European Aerosol Research Lidar Network to Establish an Aerosol Climatology (EARLINET). The objective of this research was to test the correctness of the algorithms and the influence of the lidar ratio used by the various lidar teams involved in the EARLINET for calculation of backscatter-coefficient profiles from the lidar signals. The exercise consisted of processing synthetic lidar signals of various degrees of difficulty. One of these profiles contained height- dependent lidar ratios to test the vertical influence of those profiles on the various retrieval algorithms. Furthermore, a realistic incomplete overlap of laser beam and receiver field of view was introduced to remind the teams to take great care in the nearest range to the lidar. The intercomparison was performed in three stages with increasing knowledge on the input parameters. First, only the lidar signals were distributed; this is the most realistic stage. Afterward the lidar ratio profiles and the reference values at calibration height were provided. The unknown height- dependent lidar ratio had the largest influence on the retrieval, whereas the unknown reference value was of minor importance. These results show the necessity of making additional independent measurements, which can provide us with a suitable approximation of the lidar ratio. The final stage proves in general, that the data evaluation schemes of the different groups of lidar systems work well. (C) 2004 Optical Society of America
Y1  - 2004
SN  - 0003-6935
ER  -