ISIS/Alouette Topside Sounder Data Restoration Project


The production of digitized ISIS 2 ionograms is performed using two main programs which perform the following tasks (1 - 7 in the first program and 8 - 15 in the second):

1. Line Sync Correlation: Use line sync correlation function to find best match to line sync pulse.

2. Scan Line Buffering: Build scan lines from A/D samples.

3. Video Calibration: Use video calibration waveform to correct for errors in amplitude and DC offset.

4. Frequency Marker Detection: Detect frequency markers in scan lines.

5. Frame Sync Detection: Detect frame synchronization pulse in scan lines.

6. Write Digital Ionogram: Format data and write complete digital ionogram to file.

7. Write JPEG File: Convert ionogram to JPEG image and write to file. (Note: the JPEG image files are used for quality control checks of performance up to this step; they are saved but are not forwarded to the NSSDC.)

8. Determine frame sync time in the digital ionogram file by converting the PB4 time into day of year, hour, minute, second, milisecond, microsecond.

9. Calculate world map information corresponding to the frame sync time.

10. Find frequency markers and associated times.

11. Interpolate and/or extrapolate to determine frequency of each scan line (based on frequency and time of frequency markers).

12. Extract cosmic noise (sounder receiver AGC) level and determine instrument status from the PCM data.

13. Determine averages (4 samples/average) of amplitude data.

14. Calculate delay time and apparent range.

15. Create files of non-averaged amplitudes, averaged amplitudes and header information.

Go to the ISIS/Alouette Data Restoration Home Page

For more information about the Alouette/ISIS missions, please contact Dieter Bilitza

NASA Official: J. H. King,
Last Updated: 3 November 1999, DKB