This Ionogram was digitized from the original ISIS 1 Analog Telemetry Data on 7-Track Tape using the Facilities of the Data Evaluation Laboratory at NASA GSFC, Code 500. This Data Restoration Project is headed by Dr. R.F. Benson, NASA GSFC, Code 692. Ionograms were digitized at the Rate of 40,000 16-bit samples/s. This Sample Rate is higher than the Nyquist Frequency of 30 kHz. The Sample Frequency of 40 kHz provides a Measurement every 25 ms corresponding to an Apparent Range Interval of c*t/2, where c is the Speed of Light, or 3.747 km. Each Ionogram consists of a Fixed Frequency Portion and a Swept Frequency Portion. The Time Resolution is typically 29 s.
This data product has been produced as part of the ISIS 1 topside digital ionogram database enhancement project, and this data product is one in the set of the Average Ionogram, version 2, av2, data products. Version 2 ISIS-I topside digital ionograms have been produced from the midlatitude Ottawa, OTT, the low-latitude Quito, and the high-latitude University of Alaska, Fairbanks telemetry stations. Digital ionograms from the midlatitude Santiago telemetry station are in production as of 2020-04-22. A major goal of the enhancement project is to produce as many topside soundings of ionospheric Ne(h) as possible so as to expand the Ne(h) profile coverage in latitude, longitude, and epoch. Original, version 1, files designated as 'av' for average files where the apparent-range information was averaged to yield 15-km resolution are also available. Both versions, av and av2, have good ionogram data, but the lack of proper frame-sync detection in the av files often prevented the determination of frequency information. After correcting the frame-sync detection, it is possible to add the correct frequency information allowing the ionograms to be processed automatically, by software such as TOPIST, to yield topside Ne(h).