ISIS/Alouette Topside Sounder Data Restoration Project

ISIS 2 SOUNDER AMPLITUDE INFORMATION

The color scale represents a linear sounder-receiver video amplitude output range from zero to 4.5 V expressed in terms of telemetry units from zero to 255. This calibration is based on the video calibration levels at the end of the listening period following each sounder pulse (these calibration levels produce the multi-colored stripe at the bottom of the digital ionograms). The sounder-receiver automatic-gain-control (AGC) voltage (from 0 to 5.12 volts) is obtained from a linear interpolation between the AGC trace displayed between 2400 km virtual range (16.0 ms) as 5.12 V and either 2805 km (18.7 ms) on the average ionograms or 2801.25 km (18.675 ms) on the full ionograms2805 km (18.7 ms) as 0 volts. On the average ionograms, which are available as either CDF or binary files from the NSSDC, the range resolution is 0.1 ms (corresponding to a virtual-range resolution of 15 km) there are 28 rows (27 intervals) covering the 0 to 5.12 V range; thus each row in virtual range above (decreasing delay time) the zero level (at 18.7 ms delay time) corresponds to an increase of 5.12/27 V of AGC with a quantization uncertainty of approximately plus or minus 0.1 V. Two rows have zero video-output amplitude values (on the average ionograms) in order that a clear AGC trace is visible on the ionograms. The row with the greatest virtual range corresponds to the actual AGC value. These AGC values were obtained from the pcm data corresponding to the ionogram of interest; these pcm files are available from the NSSDC. If the ionogram analysis program (also available from the NSSDC) is used, the AGC voltage corresponding to the scaling of each X- and O-mode trace point is given as part of the output file with the extension .tra. On the full ionograms, which are available as binary files from the NSSDC, the range resolution is 0.025 ms (corresponding to a virtual-range resolution of 3.75 km) and three rows have zero video-output amplitude values; the middle row corresponds to the actual AGC value.

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For more information about the Alouette/ISIS missions, please contact Dieter Bilitza
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NASA Official: J. H. King, king@nssdca.gsfc.nasa.gov
Last Updated: 3 November 1999, DKB