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Voyager 2 IRIS Raw Data Records from Neptune (PDS)


Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Time span: 1989-08-23 to 1989-08-26


This data set contains measurements from both the infrared interferometer spectrometer and the broadband reflected solar radiometer as well as ancillary data. The data are ordered by time as measured by the Flight Data System Count (FDSC). This represents the data frame number, modulo 60. Also included are pointing and other information on the geometry associated with a given data record and applicable references. Each record of the data set contains a header, radiometer observations, and interferometer observations.

The interferometer data consists of calibrated thermal emission spectra expressed as spectral radiances in W-cm/sq cm/sr. The wave number corresponding to each spectral radiance value is not included in the data set, however the beginning wave number and the constant wave number increment are given, permitting easy calculation of the appropriate wave number for each radiance. The calibrated radiances have been obtained from the directly measured interferograms of the planetary body, along with deep space calibration observations. The interferograms were first symmetrized to correct for the fact that they were not sampled at zero path difference and to remove the asymmetry due to residual dispersion in the beam splitter and compensator. The symmetrized interferograms were then apodized using a Hamming function and subsequently cosine-transformed. The responsivity obtained from the deep space measurements and knowledge of the instrument temperature were then used to obtain calibrated radiances.

The radiometer data include a measurement integrated over the 45.6 s required to take one interferogram and measurements sampled eight times during the data frame. The latter include both high and low gain measurements. A steady target yields identical signals for the eight samples each of high and normal gain data, and for the integrated data, within the resolution of each measurement. The integrating radiometer provides the best resolution (by a factor of approximately 3). However, for an accurate integrated measurement the target must remain stable in the field of view for an entire frame, which seldom happened.

This data set differs from the earlier Neptune data set, PSPA-00219, in that the spectral radiances in the earlier data sets were listed with a wave number spacing of 1.39051/cm. This represented a significant over sampling of the data for which the apodized spectral resolution is 4.3/cm. In order to make the present data set more compact, the sampling interval for the spectral radiances was reduced to 2.15/cm. This was accomplished by Fourier transforming the original data, resampling at larger intervals, and transforming back to the spectral space. It should be noted that the full intrinsic information content of the data has been preserved with this procedure, and the two forms of presentation of the data are entirely equivalent insofar as the information content is concerned.

Alternate Names

  • PDS VG2-N-IRIS-3-RDR-V1.0
  • VG2-N-IRIS-3-RDR-V1.0
  • VG2 Neptune IRIS 3 RDR V1.0


  • Planetary Science: Atmospheres


  • 77-076A-03H

Additional Information



Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II



NameRoleOriginal AffiliationE-mail
Dr. Barney J. ConrathGeneral ContactNASA Goddard Space Flight Center
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