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Data Set ID:
NmIDCS3G

Nimbus Image Dissector Camera System Remapped Visible Imagery Daily L3, GeoTIFF, Version 1

This data set (NmIDCS3G) consists of daily, global image composites constructed from Nimbus 3 and Nimbus 4 Image Dissector Camera System (IDCS) imagery for the region between 60 N and 60 S. Images were acquired between 23 April, 1969 - 04 January, 1971. Data are available as GeoTIFFs and browse images. For HDF5 formatted version of these data, see Nimbus Image Dissector Camera System Remapped Visible Imagery Daily L3, HDF5.

Geographic Coverage

Spatial Coverage:
  • N: 60, S: -60, E: 180, W: -180

Spatial Resolution:
  • 10 km x 10 km
Temporal Coverage:
  • 23 April 1969 to 4 April 1971
Temporal Resolution: 1 day
Parameter(s):
  • Visible Wavelengths > Visible Imagery
Platform(s) NIMBUS-3, NIMBUS-4
Sensor(s): CAMERAS
Data Format(s):
  • GeoTIFF
Version: V1
Data Contributor(s): David Gallaher, G. Garrett Campbell

Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Gallaher, D. and G. Campbell. 2013. Nimbus Image Dissector Camera System Remapped Visible Imagery Daily L3, GeoTIFF, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/NIMBUS/NmIDCS3G. [Date Accessed].

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Detailed Data Description

Format

Data files are available in Geographic Tagged Image File Format (GeoTIFF).

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File Naming Convention

This section explains the file naming convention used for NmIDCS3G data files.

Example file name: NmIDCS3G.[YYYY].[MM].[DD].G.tif

Refer to Table 1 for descriptions of the file name variables listed above.

Table 1. NmIDCS3G File Naming Convention
Variable Description
NmIDCS3G Product
YYYY Year (1969 or 1970)
MM Month
DD Day
G Equatorial Projection
.tif GeoTIFF
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File Size

Data files are about 16 MB.

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Spatial Coverage

Northernmost Latitude: 60° N
Southernmost Latitude: 60° S
Easternmost Longitude: 180° E
Westernmost Longitude: 180° W

Spatial Resolution

Roughly 10 km

Projection and Grid Description

Data are provided in a 10 km cylindrical equidistant projection. The grid was constructed by defining an initial 4000 east-west by 2000 north-south global array at the equator to establish roughly 10 km x 10 km cells. Only the portion of the grid from 60° N to 60° S (4000 X 1334) was saved for the final output.

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Temporal Coverage

23 April, 1969 – 04 April, 1971

Temporal Resolution

Daily

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Parameter or Variable

The parameter of interest in this data set is visible brightness. See the Data Acquisition and Processing section of this document for details.

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Software and Tools

Any GeoTIFF-compatible software package can be used to read and display NmIDCS3G data files.

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Data Acquisition and Processing

Data Acquisition Methods

To obtain the along-track scan, the IDCS rotated the sensor counter to the motion of the satellite for 200 seconds (the cross-track scan was acquired by a drift tube sensor). After 200 seconds, the sensor returned to the starting position to began the next acquisition 210 seconds after the previous image. As a result, successive images overlap each other in space by 50 percent.

The IDCS output was stored as brightness levels on a tape recorder and transmitted as an analog signal to ground stations within range of the satellite and eventually to Goddard Space Flight Center (GSFC). At GSFC, the images were reconstructed on a television picture tube and captured on black-and-white 70 mm film. The film images were then duplicated onto long reels and archived at NASA (and later NOAA). The film rolls remained in storage for some 40 years until NSIDC investigators undertook the task of digitizing the images for new climate research and preservation.

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Derivation Techniques and Algorithms

Trajectory and Attitude Data

Navigation parameters were derived from the user guide description of the instrument. Satellite ephemeris and image times were used to calculate latitude and longitude for every pixel. Although the images contained tick marks indicating lines of latitude and longitude, the investigators believe the calculated positions better align the images with identifiable landmarks.

Processing Steps

To construct the daily composites, all IDCS images for the 24 hour period were accumulated from the NmIDCS1H data set. When multiple observations were available in a grid cell, the observation closest to satellite nadir was given preference. The cosine of the selected observation's view angle is stored in the cosine_view_angle data field, for users who wish to make additional corrections based on view angle.

Error Sources

Navigation

None of the original Nimbus calibration programs have survived. In addition, the navigation accuracy is limited by the satellite attitude control, which was no better than 1 degree, and no further information about the attitude is available. By eye, the navigation and continental boundaries line up with some random error.

However, due to ambiguity in the user guide description of the instrument, the navigation has systemic errors that produce noticeable mismatches between images showing the same geographic features. This error may have arisen because the roll, pitch, and yaw of the satellite were not recorded. Based on a review of many images of the Mediterranean, navigation accuracy is better in equatorial regions.

Image Quality

The PIs estimate that the actual gray scale resolution is 4 bit, limited by the initial sensitivity of the IDCS and the accumulated degradation due to photo processing and digitization. However, the resolution is sufficient to at least qualitatively recognize clouds, ocean, land, and ice. Albedos and optical depths are likely irretrievable. Nevertherless, the IDCS represents a considerable improvement compared with the earlier AVCS instrument.

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Quality Assessment

As discussed in the Nimbus Image Dissector Camera System Visible Imagery L1, HDF5 documentation, IDCS images in these composites were calibrated by constructing individual histograms from all images in an orbit and matching histograms between many orbits. This helped remove some of the variations due to film exposure and developing. Although the calibration is not perfect, this approach yields a better composite compared with simply mixing the uncalibrated, raw images.

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Sensor or Instrument Description

The Image Dissector Camera System (IDCS) was a shutterless, electronic scan and step tube mounted behind a 108 degree wide-angle, 5.7 mm focal length lens. The camera was installed on the bottom of the satellite sensory ring and pointed vertically down toward the earth at all times. The optical field of view was 73.6 degree in the direction of flight and 98.2 degree in the plane perpendicular to flight. The instrument optics focused the image on the dissector tube's photosensitive surface, while a line-scanning beam scanned the surface at 4 Hz with a frame period of 200 seconds. At the nominal spacecraft altitude of 1100 km, the resulting pictures covered approximately 1400 km on a side with a ground resolution of 3 km at nadir. Scanning and stepping functions occurred continuously as the satellite progressed along its orbital path. Pictures were either transmitted to ground stations in real time or stored on magnetic tape for subsequent transmission.

For additional information about the Nimbus IDCS, see the National Space Science Data Center's Image Dissector Camera System (IDCS) Web page.

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References and Related Publications

Contacts and Acknowledgments

Investigators

David Gallaher
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA

G. Garrett Campbell
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA

Acknowledgements: 

The Nimbus Data Rescue Project: Nimbus 1, 2, 3 was supported by NASA contract #NNG08HZ07C as a subtask to NSIDC at the University of Colorado. The PIs also wish to thank Alex Calder, Carl Gallaher, and Anna Schroeder for their contributions to this project, and NSIDC student workers William Harris and Amy Randall.

Document Information

DOCUMENT CREATION DATE

May 2015

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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