ISIS-2 Topside Sounder Average Ionogram over Syowa Base, Antartica: SYO, Latitude -69, Longitude 40

These Ionograms were digitized from the original ISIS-2 7-Track Analog Telemetry Tapes using the Facilities of the former Data Evaluation Laboratory at the NASA/GSFC. This Data Restoration Project is headed by Dr. R.F. Benson (NASA/GSFC). 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 µs corresponding to an Apparent Range Interval equal to 3.75 km from c*t/2, where c is the Speed of Light. Ionograms with this Sample Rate are designated as 'Full' Ionograms because they have the full 3.75 km Apparent-Range Resolution. The Ionograms used for most Analyses, and those available from CDAWeb, were produced by averaging every four Samples of the Sounder-Receiver Video Amplitude Output to yield an average Value every 100 µs corresponding to an Apparent-Range Resolution of 15 km. These Ionogram Files are referred to as 'Average' Files with Standard Resolution. Each Ionogram consists of a Fixed-Frequency Portion and a Swept-Frequency Portion. The Time Resolution between Ionograms is typically 14 or 22 s depending on the Frequency Sweep Range.

本数据集所涉电离图（Ionogram）源自原始ISIS-2卫星7轨模拟遥测磁带，由美国国家航空航天局戈达德太空飞行中心（NASA/GSFC）前数据评估实验室的设备完成数字化处理。本数据修复项目由R.F.本森博士（NASA/GSFC）牵头负责。电离图的数字化采样速率为每秒40000个16位采样点，该采样率高于30 kHz的奈奎斯特频率（Nyquist Frequency）。40 kHz的采样频率每25微秒完成一次采样，结合光速（Speed of Light）与公式c*t/2计算，对应的视距间隔为3.75千米。采用该采样率的电离图被称为'Full'电离图，因其具备完整的3.75千米视距分辨率。多数分析研究所用以及可从CDAWeb获取的电离图，是将测深仪接收机（Sounder-Receiver）的视频幅度输出信号每4个采样点进行平均，每100微秒生成一组平均数值，对应的视距分辨率为15千米。此类电离图文件被称为'Average'标准分辨率文件。每张电离图均包含固定频段与扫频频段两部分。电离图之间的时间分辨率通常为14秒或22秒，具体取决于扫频范围。