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The CCD/Transit Instrument (CTI) data-analysis systemThe automated software system for archiving, analyzing, and interrogating data from the CCD/Transit Instrument (CTI) is described. The CTI collects up to 450 Mbytes of image-data each clear night in the form of a narrow strip of sky observed in two colors. The large data-volumes and the scientific aims of the project make it imperative that the data are analyzed within the 24-hour period following the observations. To this end a fully automatic and self evaluating software system has been developed. The data are collected from the telescope in real-time and then transported to Tucson for analysis. Verification is performed by visual inspection of random subsets of the data and obvious cosmic rays are detected and removed before permanent archival is made to the optical disc. The analysis phase is performed by a pair of linked algorithms, one operating on the absolute pixel-values and the other on the spatial derivative of the data. In this way both isolated and merged images are reliably detected in a single pass. In order to isolate the latter algorithm from the effects of noise spikes a 3x3 Hanning filter is applied to the raw data before the analysis is run. The algorithms reduce the input pixel-data to a database of measured parameters for each image which has been found. A contrast filter is applied in order to assign a detection-probability to each image and then x-y calibration and intensity calibration are performed using known reference stars in the strip. These are added to as necessary by secondary standards boot-strapped from the CTI data itself. The final stages involve merging the new data into the CTI Master-list and History-list and the automatic comparison of each new detection with a set of pre-defined templates in parameter-space to find interesting objects such as supernovae, quasars and variable stars. Each stage of the processing from verification to interesting image selection is performed under a data-logging system which both controls the pipe-lining of data through the system and records key performance monitor parameters which are built into the software. Furthermore, the data from each stage are stored in databases to facilitate evaluation, and all stages offer the facility to enter keyword-indexed free-format text into the data-logging system. In this way a large measure of certification is built into the system to provide the necessary confidence in the end results.
Document ID
19960000872
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Cawson, M. G. M. (Arizona Univ. Tucson, AZ, United States)
Mcgraw, J. T. (Arizona Univ. Tucson, AZ, United States)
Keane, M. J. (Arizona Univ. Tucson, AZ, United States)
Date Acquired
September 6, 2013
Publication Date
October 6, 1995
Subject Category
Computer Programming And Software
Report/Patent Number
NAS 1.26:199440
NASA-CR-199440
Accession Number
96N10872
Funding Number(s)
CONTRACT_GRANT: NAGW-804
CONTRACT_GRANT: NSF AST-83-14787
CONTRACT_GRANT: NAGW-121
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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