ISIS-2 Topside Sounder Average Ionogram over Lauder, New Zealand: LAU, Latitude -45, Longitude 170

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.

本批电离图（Ionogram）源自原始ISIS-2 7轨模拟遥测磁带，由美国国家航空航天局/戈达德航天飞行中心（NASA/GSFC）原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。
本次数字化采样率为40000个16位采样/秒，该采样率高于30千赫兹的奈奎斯特频率（Nyquist Frequency）。40千赫兹的采样频率每25微秒完成一次测量，结合公式c·t/2（其中c为光速）可得到对应3.75千米的视距间隔。此类具备该采样率的电离图被称为“全分辨率”电离图，因其拥有完整的3.75千米视距分辨率。
多数分析所用及可从CDAWeb获取的电离图，是将探测仪-接收机视频振幅输出的每4个采样点取平均后生成的，每100微秒输出一次平均值，对应15千米的视距分辨率。此类电离图文件被称为“标准分辨率平均”文件。
每张电离图均包含固定频率部分与扫频部分。两张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。