Data Set ID: 
NmTHIR67-3G

Nimbus Temperature-Humidity Infrared Radiometer 6.7 µm Water Vapor Remapped Digital Data Daily L3, GeoTIFF, Version 1

This data set (NmTHIR67-3G) consists of daily, global composites of radiative temperatures obtained in the 6.7 µm water vapor window (6.5 µm - 7.0 µm) by the Temperature-Humidity Infrared Radiometer (THIR) on board the Nimbus 4 satellite. The THIR 6.7 µm window was used to map the water vapor distribution in the upper troposphere and stratosphere. Data files are GeoTIFF versions of the HDF-formatted equatorial projection file only from the Nimbus Temperature-Humidity Infrared Radiometer 6.7 µm Water Vapor Remapped Digital Data Daily, HDF5 (NmTHIR67-3H) data set.

This is the most recent version of these data.

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Parameter(s):
  • Infrared Wavelengths > Infrared Imagery
  • Atmospheric Water Vapor > Water Vapor
Data Format(s):
  • GeoTIFF
Spatial Coverage:
N: 60, 
S: -60, 
E: 180, 
W: -180
Platform(s):Nimbus-4
Spatial Resolution:
  • 20 km x 20 km
Sensor(s):THIR
Temporal Coverage:
  • 10 May 1970 to 25 March 1971
Version(s):V1
Temporal Resolution1 dayMetadata XML:View Metadata Record
Data Contributor(s):David Gallaher, G. Garrett Campbell

Geographic Coverage

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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. 2015. Nimbus Temperature-Humidity Infrared Radiometer 6.7 µm Water Vapor Remapped Digital Data Daily L3, GeoTIFF, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/NIMBUS/NmTHIR67-3G. [Date Accessed].

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Detailed Data Description

The THIR detected emitted thermal radiation in two windows: 6.7 µm (6.5 µm — 7.0 µm) and 11.5 µm (10.5 µm — 12.5 µm). This data set contains Nimbus-4 THIR 6.7 µm window data for the region between 60° N and 60° S. The corresponding THIR 11.5 µm window measurements are available as a separate data set here.

Simultaneous observations from the 6.7 µm and 11.5 µm windows are typically not available. Although measurements sometimes overlap, most do not.
Format

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

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File Naming Convention

This section explains the file naming convention used for NmTHIR67-3G data files. Daily composites are divided into ascending/day (up) and descending/night (down) orbit halves. As such, two GeoTIFF files are available per solar day.

Example File Name: NmTHIR67-3G.DownWV.1970.05.10.G.tif

NmTHIR67-3G.[UpWV/DownWV].[yyyy].[mm].[dd].[p].tif

Refer to Table 1 for the valid values for the file name variables listed above.

Refer to Table 1 for the valid values for the file name variables listed above.

Table 1. File Name Variable Descriptions
Variable Description
NmTHIR67-3G Nimbus-4 THIR 6.7 µm window daily composite (GeoTIFF)
UpWV/DownWV Orbit half: Up (day) or Down (night), water vapor
yyyy Four-digit year
mm Month
dd Day
p Projection: G (equatorial)
.tif GeoTIFF file
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File Size

Data files typically about 4 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 20 km

Projection and Grid Description

Data are provided in a 20 km cylindrical equidistant projection. The grid was constructed by defining a 2000 east-west by 664 north-south global array at the equator to establish roughly 20 km x 20 km cells. Only the portion of the grid from 60° N to 60° S (2000 X 664) is saved for the final output.

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Temporal Coverage

Intermittent data are available from 10 May 1970 to 25 March 1971

Temporal Resolution

Daily

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Parameter or Variable

Variable Description

The parameter of interest in this data set is infrared brightness temperature in the 6.7 µm water vapor window. 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 this data set's files.

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Data Acquisition and Processing

Data Acquisition Methods

The THIR on the Nimbus 4 satellite transformed measured radiation into electrical voltages that were recorded on tape and played back when the satellite came within range of a receiving station. These data were then transmitted to the Goddard Space Flight Center (GSFC), where they were calibrated, converted to temperatures, and archived on 7-track, digital magnetic tapes. In 2013, the contents of these tapes were recovered and written to a binary tape emulation file format (TAP) for preservation. GES DISC, the NASA Goddard Earth Sciences Data and Information Services Center, maintains a Nimbus Overview page through which users can obtain the TAP files and historical Nimbus documentation such as instrument user guides and mission reports.

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Derivation Techniques and Algorithms

Processing Steps

To construct the daily composites, all reprocessed THIR swaths for each 24-hour period were accumulated from the Nimbus Temperature-Humidity Infrared Radiometer 6.7 µm Water Vapor Swath L1, HDF5 (NmTHIR67-1H) data set. When multiple observations were available in a grid cell, the observation closest to satellite nadir was selected.

The underlying THIR swath data have been corrected to minimize seemingly random alignment errors that caused cloud edges and land features to appear jagged. See Derivation Techniques and  Algorithms in the NmTHIR67-1H documentation for details.

Error Sources

This data set was constructed from archival files at GES DISC. As such, they reflect the original THIR calibration and temperature conversion utilized in 1970. Furthermore, most of the mosaics have large areas of missing data because the Nimbus 4 project only captured select data based on operational considerations in the 1970-1971 time frame.

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Quality Assessment

The realignment described in the preceding section improves the visual appearance of the data and better represents the shapes of clouds and coastlines. In regions with very little spatial information, for example where the measurements are very noisy or very uniform, the shifts offer little or no improvement.

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Sensor or Instrument Description

The Nimbus 4 Temperature-Humidity Infrared Radiometer (THIR) was a two-channel scanning radiometer designed to detect emitted thermal radiation in two windows: 6.7 µm (6.5 µm — 7.0 µm) and 11.5 µm (10.5 µm — 12.5 µm). The 6.7 µm window operated primarily at night and was used to map the distribution of water vapor in the upper troposphere and stratosphere. The 11.5 µm channel operated both day and night and measured cloud top or surface temperatures.

The Nimbus 4 instrument utilized a single scan mirror which rotated at 48 rpm and was inclined 45° to the axis of rotation to scan perpendicular to the flight path. The field of view scanned across the earth from east to west in daytime and west to east at night, traveling northward and southward respectively. Incoming energy was collected by the mirror and then focused into a dichromatic beam splitter which divided the energy spectrally and spatially into the two channels. Both channels transformed the received radiation into an electrical (voltage) output with an information bandwidth of 0.5 Hz to 120 Hz for the 6.7 µm channel and 0.5 Hz to 360 Hz for the 11.5 µm channel. The data were recorded on tape and subsequently played back to a ground acquisition station.

The THIR intially operated successfully but failed on January 11, 1971 (orbit 3731). It was restarted several times thereafter for very short periods before finally ceasing all operations in August 1971. For additional information about the Nimbus THIR, see the NASA National Space Science Data Center Temperature-Humidity Infrared Radiometer (THIR) Web page.

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Version History
Version (Date) Details
V1 (24 November, 2015) Initial release.
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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

Acknowledgments: 

The Nimbus Data Rescue Project was supported by NASA contract #NNG08HZ07C as a subtask to NSIDC at the University of Colorado. The PIs also wish to thank Dennis Wingo and Matt Sandler who contributed to this project.

Document Information

DOCUMENT CREATION DATE

November 2015

No technical references available for this data set.

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