Table 1

Algorithms used in Rejecting Potential Dark Count Rate Data

Reason for Rejection Correction Stage* Algorithm Comments
Star Presence A Status bit in raw data = 0 Minimum of two successive frames must indicate star presence.
Star in vicinity of slit B Visual inspection of suspect data. Data is automatically flagged by comparing time of data with known times for pointing at bright stars. Checking for anomalies in the mean errors is used to flag cases of faint stars being near slit unexpectedly.
Presence of geocoronal Lyman Alpha emission. A Data from tube U1 is discarded if the carriage 1 encoder is between 403914 and 404014 (1215.67 Å ± 0.08 Å).
Pointing at Sunny Earth** C
  1. If U3<50, and V3>=20,000, data for V3 is discarded.
  2. If U3>=50 and V3/U3>250, data for V3 is discarded.
  3. If U3>=300 and V3/U3>100, data for V3 is discarded.
If any of these three tests are positive and the V1 encoder value is >472000 (2980 Å), V1 data is also discarded, or if V2 encoder value is >400000 (2700 Å), V2 data is discarded.*** If any point on V1, V2, or V3 is discarded based on the above algorithms, the previous and succeeding 3 points on the same tube are also discarded.

* Correction Stages: A = first run of binary data, leading to punched cards with individual data points labeled (LAN, TSN).
B = modification of punched cards
C = averaging of data from different times but common (LAN,TSN), leading to a table of predicted dark counts.

** When pointing at the sunny earth, the V3 count rate is greater than 90000/14 sec (V3 is a fixed monitor at 3428 Å ± 1 Å), but U3 is unaffected (U3 is at 1320 Å). The comparisons with U3 data (algorithms 1, 2, and 3) are made to check that a V3 count rate is not high just because of the effect of the South Atlantic Anomaly, which also raises the U3 count rate.

*** V1 and V2 are unaffected by light from the sunny earth if the wavelengths are lower than those quoted for the respective tubes. No evidence for any detectable sunny earth signal on U1, U2, or U3 has been found.

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