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ISIS 2 Topside Sounder Ionograms

Published by NASA Space Physics Data Facility (SPDF) Data Services | National Aeronautics and Space Administration | Catalog Last Checked: June 23, 2026 at 09:08 PM | Dataset Last Updated: June 22, 2026
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/sec. This sample rate is higher than the Nyquist frequency of 30 kHz. The sample frequency of 40 kHz provides a measurement every 25 microseconds corresponding to an apparent range (c*t/2) interval of 3.75 km. 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 analysis, 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 microseconds 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 and and a swept-frequency portion. The time resolution between ionograms is typically 14 or 22 seconds depending on the frequency sweep range.

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Complete Metadata
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accessLevel public
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description 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/sec. This sample rate is higher than the Nyquist frequency of 30 kHz. The sample frequency of 40 kHz provides a measurement every 25 microseconds corresponding to an apparent range (c*t/2) interval of 3.75 km. 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 analysis, 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 microseconds 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 and and a swept-frequency portion. The time resolution between ionograms is typically 14 or 22 seconds depending on the frequency sweep range.
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identifier /SDE/SPASE_JSON/|c7b50e8914d7c33481152da4a1d41c7a
keyword 
[
  "akr",
  "ducted-echoes",
  "fai",
  "field-aligned-irregularities",
  "fixed-and-swept-frequency-sounder",
  "ground-echoes",
  "ground-reflections",
  "ionospheric-echoes",
  "ionospheric-reflections",
  "plasma-resonance",
  "plasma-waves",
  "solar-type-iii-bursts",
  "spectrum-ionogram",
  "topside-ionosphere",
  "topside-sounder",
  "upper-hybrid-noise-band",
  "wave-scattering",
  "waves-active"
]
license https://www.usa.gov/government-works
modified 2026-06-22
programCode 
[
  "026:000"
]
publisher 
{
  "name": "NASA Space Physics Data Facility (SPDF) Data Services",
  "@type": "org:Organization"
}
theme 
[
  "Heliophysics"
]
title ISIS 2 Topside Sounder Ionograms

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