Feature Extraction Dmitry Chirkin LBNL Ice Cube Collaboration

Feature Extraction Dmitry Chirkin, LBNL Ice. Cube Collaboration meeting in Berkeley, March 2005

What is Feature Extraction Given an ATWD or FADC waveform, determine arrival times of all photons which contributed: • hit series • FEInfo: combination or leading edge, width, charge (or amplitude) Also applicable to AMANDA TWR

Feature Extraction last fall (DFL data) Fitted function: p 0+A 0 exp(-(t-t 0)/s 0)(1 -exp(-(t-t 0)2/s 02))

New “features” discovered since • undershooting: 1 m. V for 50 m. V pulse (Christopher Wendt): +~(exp(-(t-t 0)/dt)-1) • possible extra late pulse (PMT anode configuration artifact) (Shigeru Yoshida) fit independetly • pedestal drift (corrected for by the fat-reader)

Multi-peak fit • find first peak using the existing algorithm (refined with the root fit) • construct difference with the fitted function, weight by 1/F(waveform) to emphasize all peaks (big and small) • find maximum and add SPE fit function with t 0 close to it

Multi-peak fit (cont. ) • Fit the sum of two SPE functions to the waveform • repeat for all SPE terms with amplitude above threshold until the quality of the fit stops improving

In-Ice Fits (low PEs)

In-Ice Fits (high PEs)

Ice. Top Fits

Other feature extraction “features” • other fitting functions were tried: log-normal (by Tom Mc. Cauley) provides a different description of the rising leading edge • the undershooting is now fitted, so higher ATWD channels should be used not only for saturated values, but also for values close to 0 zero-suppression road grader algorithm needs be modified to suppress the “most-repeated value” instead of 0 • the higher ATWD channels are narrower, creating extra “mismatch” peak at the trailing edge. higher-channel peaks need to be widened before they are combined with channel 0

Other feature extraction “features” • a “slewing” correction (shift of the leading edge proportional to width) may need to be made to the leading edge to describe electronics delays Laser DFL or flasher inice calibration? • another correction proportional to high-voltage needs must made to describe high-voltagedependent delay of the developing signal in the PMT Laser DFL calibration should be sufficient?

Ice. Tray FE implementation Feature. Extractor is a project on glacier, a part of: • OFFLINE-SOFTWARE • FATDATA example script is in the fat-reader/resources/ directory you can control: • Max. Num. Hits: maximum number of separate SPE functions to be fit, if necessary (default 20) • through the “Data. Options” of the fat-reader select hits that only pass a certain fraction of SPE threshold (--thrs) At this time hidden in the source code: • maximum SPE waveform width – reduce it to split up large pulses into smaller ones (default 6 bins) • fixed parameters for the description of undershooting

Feature. Extractor usage and dataclasses • ATWDChannel. Merger must be plugged in to produce the Combined. ATWD waveform used by the Feature. Extractor • I 3 DOMCalibration class was modified to accommodate calibration and combining of the ATWD channels of different size: now Set methods set by ATWD bin “name”, 0 -127 in reversed time order, as before now Get methods get by the time-ordered ATWD bin number, 0 -127 in correct time order this changed need not worry about this if only combined ATWD traces or Feature-Extracted hits are used

Conclusions • possibility to fit multi-peak waveforms was a highly-anticipated feature, which should be considered a major improvement • precision of the multi-peak fits for complicated waveforms is proportional to the time one is willing to spend on extracting features from waveforms: from a few milliseconds for 2 -3 peaks to a few seconds for 10 to a few dozen seconds for 20. • ATWDChannel. Merger and I 3 DOMCalibration class were modified to accommodate for hits with different ATWD-channel sizes (e. g. , currently for in-ice: 128, 32) • Feature. Extractor is a part of both OFFLINE-SOTWARE, and FATDATA. For the Feature. Extractor development the FATDATA provides a more versatile environment, allowing for a fast selection of the high- or low-PE events.

Road-grader zero-suppression Common SPE-like waveform: • pedestal is shifted down compared to the value expected from calibration. This is a well-known (by now) effect and is corrected by the fatreader • ok to use roadgrader as is

Road-grader zero-suppression A large-amplitude, saturated waveform: • undershoot is not recorded by the current road-grader implementation, but is a part of the waveform “features”

Road-grader zero-suppression Highly-saturated muti -PE waveform: • the undershooting and small pulses on top of the undershot tail are all suppressed by the road-grader. Both amount of the undershooting and small pulses are features of the waveform and are used/reconstructed by the Feature. Extractor

Road-grader proposed modifications • find the “most-repeated” value, and compress all values above and below it (no more than a threshold-setting away) this requires one pass over the incoming waveform and a small (~256 byte) memory buffer the zero-suppressed value itself should be encoded into the compressed data • to make word length more uniform (11 bits all the time), prepend the 10 -bit number of the next zero-suppressed words with “ 1”, and all other (10 -bit) values with “ 0”. This is more uniform (and possibly efficient) than the current road-grader + Huffman-encoding algorithm

Modified road-grader compression ratio Dawn’s MPE set Dawn’s SPE set