DATA PROCESSING LOG FORMAT (TRACKING STATIONS TO VSOG) Y. Murata, ISAS Dec 14, 1996 1. INTRODUCTION This document specifies how recording log information as well as certain calibration information and error flags will be supplied by the tracking stations to the VSOP Science Operations Group (VSOG). It is based on [1], [2], and [3]. Please note that this specification is concerned ONLY with the supply of data from the tracking stations to the VSOG, and not with the supply of input logs to the correlator or of calibration and flag information to the end users (correlators and principal investigators). This log has been given the name "Data Processing Log", because it contains several different types of data needed for correlator processing or for science data calibration. Generally, all information of "log type" will be supplied in the Data Processing Log, unless a provision has been made to supply it differently. "Log type" means information that is gathered in real time during an observation (tracking pass). The data do not need to be recorded in chronological order, but they must be time-tagged; the VSOG will read this file with the log entries in any order. If the tracking stations expect that other operational elements may read the file (which is not nominal), time-ordered records may be desired. All information in the Data Processing Log will be supplied to the VSOG in the form of the correlator log file that was specified in [2] and [3]. This specification is only used for the format; the final contents for the input logs to be supplied from the VSOG to the correlators are given in [2] and [3]. Four specific data types will be included as part of the Data Processing Log. Three are required: correlator input data; tone extraction data; and error flags. The fourth data type, which is optional, is square-law detector data. 2. RECORD SPECIFICATIONS The notation of [2] is adopted for giving the syntax of each of the four record types. 2.1 Correlator Input Data All correlator input data available from the tracking stations must be supplied in the Data Processing Log according to the specification of the VLBA correlator input log given in [2], or the S2 correlator input log given in [3]. 2.2 Tone Extractor Record The Tone Extractor Record has the form yydddhhmmssxx/TONE/,,, where is the channel designator, identical to the field in a "BBC" record that precedes this "TONE" record in the log (in the case of no "BBC" record, use "A" and "B" for VSOP sampler channel "A" and "B", respectively); is the baseband frequency, in MHz, of the tone whose amplitude and phase have been measured; is the measured amplitude, as a fraction of the total rms signal level in the channel; is the measured phase, in degrees, relative to the data clock. 2.3 Flag Record The Flag Record has the form yydddhhmmssxx/FLAG/,[,] where is an integer specifying a particular error type; is an integer from 0 to 2, indicating the present severity of the error, as follows: 0 no error - a previously indicated error condition no longer exists 1 warning - the specified error exists, but may not have a significant effect on the quality of the observation now in progress; 2 severe - the specified error exists, and the present observation is almost certain to be adversely affected. The optional is a string, in double quotes, of at most 64 characters, giving a brief description of the error; this is intended for human readers of the file, so no automatic procedures (software) should depend on its existence or contents. The values of and shall be taken from the list given in [4]. This list contains a full explanation (not limited to 64 characters) of each error type. A FLAG record type shall be included in the file whenever the value of a given error CHANGES. In particular, a record is included with =0 if the condition previously had non-zero . At the beginning of a tracking pass, occurring at the time specified by the TSID record (see [2]), all errors are assumed to have =0 until the time when a FLAG record is specified. 2.4 Square Law Detector Record The Square Law Detector Record is optional; the VSOG will normally choose to compute the amplitude calibration based on the downlink telemetry headers and other information available to the VSOG. It is anticipated that the Square Law Detector Record will be supplied to the VSOG only from the Green Bank Earth Station. The Square Law Detector Record has the form yydddhhmmssxx/SQLD/,,,,,,..., where is a decimal number proportional to the total power measured in channel #i at the given time, and is a decimal number proportional to the switched power measured in the same channel at the same time. Here "total power" refers to the measured power when the calibration noise source is OFF, and "switched power" refers to the difference between the power with the noise source ON and the power with the noise source OFF. The absolute scale of these values is arbitrary, but the two numbers from one channel must have the same scale. As indicated by the word "proportional," any known zero offset must have been removed. is the power spectral density of the calibration noise source for channel #i, in Kelvins, at the given time, referred to a known reference plane in the receiving system's signal path. Channel numbers follow a fixed sequence defined for each telescope. Data may be omitted (e.g., for channels not currently in use) by leaving the corresponding field blank or empty, but all delimiters (commas) must be included. Notes: This record type is applicable only to telescopes having a switched calibration noise source that adds a known (preferably constant) amount of noise spectral density to the astronomical signal when on; and having a synchronously-switched square law detector on each signal channel immediately prior to digitization (typically at baseband). Both VSOP and RadioAstron include these features, as do most ground radio telescopes used for VLBI. Corrections for known hardware errors or peculiarities in a particular telescope (e.g., temperature dependence or non-linearity of the detectors) should have been applied if possible. We give in each record even though it is normally constant in order to allow for its variation with temperature or other influences. Under these conditions, the best available estimate of the GAIN from the reference plane to the digitizer is / (in arbitrary units), and the best available estimate of the SYSTEM TEMPERATURE is */ (in Kelvins). REFERENCES [1] L. D'Addario, "Calibration and flagging data from the NRAO OVLBI Earth Station at Green Bank, Appendix A," March 12, 1996. [2] J. Romney, "Alternative log input to the VLBA correlator for space VLBI operations," July 1, 1996. [3] B. Carlson et al., "SVLBI Space Radio Telescope Log Input to the Canadian S2 Correlator," August 17, 1996 (to be revised). [4] J. Ulvestad et al., "Flag dictionary for space radio telescope log files," version 2.0, February 19, 1996.