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Nimbus Advanced Vidicon Camera System Visible Imagery L1, HDF5, Version 1
The Nimbus Advanced Vidicon Camera System Visible Imagery L1, HDF5 (NmAVCS1H) data set consists of black-and-white images captured by the Advanced Vidicon Camera Systems onboard the Nimbus 1 (1964) and Nimbus 2 (1966) satellites. Data are provided as HDF5-formatted files. Browse images are also available.
|Temporal Resolution:||91 second|
|Data Contributor(s):||David Gallaher, G. Garrett Campbell|
|Metadata XML:||View Metadata Record|
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 Advanced Vidicon Camera System Visible Imagery L1, HDF5, 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/NmAVCS1H. [Date Accessed].
Detailed Data Description
Data are provided as HDF5-formatted files. HDF-EOS (Hierarchical Data Format - Earth Observing System) is a self-describing file format based on HDF that was developed specifically for distributing and archiving data collected by NASA EOS satellites. For more information, visit the HDF-EOS Tools and Information Center. Browse images are also available.
This section explains the file naming convention used for NmAVCS1H data files.
Example file name:
Refer to Table 1 for descriptions of the file name variables listed above.
|CC||Camera number (01 = left, 02 = nadir, 03 = right)|
|YYYY||Year (1964 or 1966)|
|01||Day of year follows|
|DDD||Day of year|
|01||Visual impression of quality follows|
|Visual impression of quality (01=Failed, 02=Passed)|
|[Cx.Cy]||Cx = center pixel (left to right) trimmed image|
|Cy = center pixel (top to bottom) trimmed image|
|[Tx.Ty]||Tx = image center (x-direction) raw TIFF file|
|Ty = image center (y-direction) raw TIFF file|
|Tn||Image number within the orbit|
Data files typically range between 3 MB - 6 MB.
Coverage is global, however some regions (parts of Alaska, for example) are not available due to technological limitations at the time of the mission. Individual images cover approximately 1000 km X 1000 km.
Roughly 2 km.
Estimated latitude and longitude is provided for each pixel.
Intermittent images are available for Nimbus 1 from 28 August to 22 September, 1964 and for Nimbus 2 from 15 May to 30 August, 1966. The Granules by Day page lists the number of granules that were produced for each day of the data record.
The AVCS consisted of three earthward-facing cameras deployed in a fan-like array to produce three-image composite pictures (see Instrument Description below). Each image triplet is effectively an instantaneous snapshot taken every 91 seconds along the satellite's polar orbit.
Each data file contains an array of 8-bit gray scale values, estimates of the latitude and longitude for each pixel, a gray scale calibration map, and a non-data/data quality mask.
Table 2 describes the data fields and corresponding attributes stored in NmAVCS1H data files.
|brightness||Array of 8 bit gray scale values||DOI||10.5067/NIMBUS/NmAVCS1H|
|ESDT||NmAVCS1H (data set short name)|
|long_ESDT||Nimbus Advanced Vidicon Camera System Visible Imagery L1, HDF5 (data set long name)|
|byte_calibration||Gray scale calibration map||units||1|
|latitude||Array of pixel latitudes||units||degrees_north|
|longitude||Array of pixel longitudes||units||degrees_east|
|quality||Non-data/quality mask (see key below)||none||n/a|
|time since 1970||Image acquisition date and time in seconds since 00:00:00, 01 January 1970||units||s|
The quality data field flags array locations in the brightness data field that contain image noise and "non-data." Non-data refers to title text, legends, fiducial marks, and latitude and longitude reference lines that were overprinted on the original film images. Use the key in Table 6 to decode the values stored in the quality data field:
|10||Latitude/Longitude Reference Lines|
|60||Lower Left Corner|
|100||Gray scale colorbar|
Gray Scale Calibration
The byte_calibration data field contains the gray scale mapping used to reduce differences in brightness between images due to variations in film developing. Although the film images included a crude calibration wedge, it was not found to be useful. As such, the PIs calibrated the images by constructing individual histograms from all images in an orbit and matching histograms between many orbits.
Software and Tools
Data Acquisition and Processing
The Advanced Vidicon Camera System (AVCS) in effect acquired a snapshot every 91 seconds along the satellites' polar orbits. A vidicon pickup tube scanned the images and recorded brightness levels to a tape recorder. These data were then 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 35 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.
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.
The PIs received the AVCS images on 400-foot rolls of 35 mm, black-and-white film comprising many days of data. NSIDC researchers and staff scanned the film images, including margins, to 8-bit TIFF files. The 8-bit scanning depth exceeds the true gray scale resolution. The images were also oversampled in space to ensure a strong correlation between adjacent pixels.
The digitized images were first trimmed and then evaluated with specially written software that allowed an operator to identify the center point from fiducial marks and read the image time. Latitudes and longitudes were then estimated for every pixel based onsatellite ephemeris and image acquisition time. Intermediate files were inspected visually and flagged for quality, and then final images were written to HDF5-formatted files.
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.
The PIs estimate that the actual gray scale resolution is 4 bit, limited by the initial sensitivity of the AVCS 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.
These data should be considered semi-quantitative. Features such as ocean and land areas and weather and sea ice variations are typically distinguishable. Subtle changes in the land surface, however, have been lost due to variations in photographic processing and should be treated with caution. For example, although these data can reveal historical storm tracks and sea ice boundaries, they would not be suitable for radiation budget studies.
The Advanced Vidicon Camera System (AVCS) consisted of three earthward-facing cameras deployed in a fan-like array to produce a three-segment, composite picture. Each camera's field of view covered 37 degree; the center camera pointed straight down while the optical axes of other two was directed 35 degree to either side. The cameras utilized an f/4 lens with a focal length of 16.5 mm. A potentiometer attached to the solar array controlled the lens opening from f/16 when the spacecraft was over the equator to f/4 when it was near the poles. Eight-hundred scan-line, 2.54-cm-diameter vidicon pickup tubes yielded a linear resolution of better than 1 km at nadir from an altitude of 800 km. The camera array produced a composite picture covering an area of 830 km by 2700 km.
For additional information about the Nimbus AVCS, see the National Space Science Data Center's Advanced Vidicon Camera System (AVCS) Web page.
References and Related Publications
Contacts and Acknowledgments
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
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 CREATION DATE