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Nimbus High Resolution Infrared Radiometer Digital Swath Data L1, HDF5, Version 1
The Nimbus High Resolution Infrared Radiometer Digital Swath Data L1, HDF data set (NmHRIR1H) consists of High Resolution Infrared Radiometer (HRIR) brightness temperatures obtained by the Nimbus 1, Nimbus 2, and Nimbus 3 satellites during 1964, 1966, and 1969. A correction has been applied to minimize seemingly random alignment errors that caused clouds edges and land features to appear jagged in the original 1960s data.
|Temporal Resolution:||5 minute|
|Platform(s)||NIMBUS-1, NIMBUS-2, NIMBUS-3|
|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 High Resolution Infrared Radiometer Digital Swath Data 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/NmHRIR1H. [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 NmHRIR1H data files.
Example file name:
Refer to Table 1 for descriptions of the file name variables listed above.
|ggg||Granule number from each orbit|
Data files are typically 1 MB to 2 MB.
Coverage is global. However, due to mission objectives and technological limitations of the time, coverage is more consistent in some areas (for example North America) and absent from others (for example portions of Alaska).
Projection and Grid Description
Intermittent data are available within the following date ranges:
|Nimbus 1||29 August to 22 September, 1964|
|Nimbus 2||16 May to 15 November, 1966|
|Nimbus 3||23 April, 1969 to 20 January, 1970|
Each file contains 5 minutes of swath data.
Table 3 lists the data fields and corresponding attributes stored in NmHRIR1H data files.
|Flags||Bit flags. See Table 4 for descriptions.||Key||key = bits 0,1: 00=ocean, 01=25% land, 10=50% land, 11=land; bit 2: on=ascending, off=descending; bit 3: on = day, off=night; bit 4 on=bad data, reflection from spacecraft; bit 5=spare; bit 6 on = temperature out of range; bit 7 on = IR filter in optical path (Nimbus 3 only)|
|HRIR-Temp||Brightness temperature (kelvin) from the 3.4 µm to 4.2 µm near-infrared region, as derived in the 1960s. Data values have been shifted spatially to help offset random alignment errors. See Derivation Techniques and Algorithms for details.||DOI||10.5067/NIMBUS/NmHRIR1H|
|ESDT||NmHRIR1H (data set short name)|
|long_ESDT||Nimbus High Resolution Infrared Radiometer
Digital Swath Data Level 1 (data set long name)
|Sat Latitude||Satellite latitude (at nadir) when scan line was acquired||units||degrees|
|Sat Longitude||Satellite longitude (at nadir) when scan line was acquired||units||degrees|
|cosine Sun Zenith||Cosine sun zenith angle from satellite nadir||units||1|
|cosine view angle||Cosine view angle of observation||units||1|
|scan Time millisec||Time scan line was acquired (ms since 1970)||units||millisecond|
|shift||Alignment shift applied to each scan line (pixels)||units||pixels|
|0, 1||Ocean/Land Coverage Flag: 00=ocean, 01=25% land, 10=50% land, 11=land|
|2||Ascending/Descending Half of Orbit: 0=descending; 1=ascending|
|3||Day/Night Flag: 0=night, 1=day|
|4||Reflected Light. Flag set to on means bad data due to reflected light from satellite component.|
|5||Spare. Set to 0.|
|6||Data Out of Range. Flag set to on means T < 190k or T > 330k.|
|7||Daytime Observation. Flag set to on means filter is in optical path (Nimbus 3 only). See Error Sources for details.|
Software and Tools
Data Acquisition and Processing
The HRIR on the Nimbus I, II, and III satellites 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 2009, 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, archives and distributes these data and maintains historical Nimbus documentation such as instrument user guides and mission reports.
In the original HRIR data, cloud edges and land features appear jagged. Closer inspection reveals that adjacent scan lines appear to be shifted relative to each other by plus or minus several pixels in the cross-track direction. These small, random shifts likely reflect some kind of systemic error, due perhaps to repeatedly switching data acquisitions on and off to record only the earthward-facing portion of each scan mirror revolution.
To help minimize this error, reference scan lines were created by smoothing the data with a moving average (n=5). Each unsmoothed scan line was then incrementally shifted in the cross-track direction (maximum of ±10 pixels) and correlated at each step with its smoothed counterpart. Brightness temperatures from the original HRIR data files were then written to the HRIR-Temp data field, offset by the pixel value that yielded the best correlation. Emptied pixels at the ends of scan lines were filled with a value of 3.4028235E+38. Each scan line's shift value is recorded in the shift data field.
Most extant Nimbus 1 and 2 observations were collected at night, however a few daytime orbits have survived. Although the daytime measurements are contaminated by reflected solar radiation, these data have been included for their qualitative and historical value.
Whereas Nimbus I and II operated almost exclusively in nighttime mode, Nimbus III was equipped with an infrared filter that could be inserted into the optical path to acquire daytime reflected solar radiation. However, no flag was set in the data to indicate whether the filter was in or out. Furthermore, a few daytime orbits were collected with no filter in place and contain mixed IR and visible radiation.
In general, daytime orbits appear to correspond to temperatures below 150 K. Bit 7 in the Flags data field is set to on to indicate the PIs' best guess that the filter was in place. Although no calibration exists for the daytime visible data, obvious distinctions between land, cloud, water, and ice surfaces are apparent. However, the visible observations are so scattered in time and space that constructing land surface or cloud maps from these data alone would result in significant sampling errors.
The realignment 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.
The HRIR on Nimbus I and II was a single scanning radiometer that operated in the 3.4 µm to 4.2 µm near-infrared region. The instrument utilized an optical system and a lead selenide photoconductive detector cell to obtain measurements of blackbody temperatures from 210K – 330K. To allow daytime operation, the Nimbus III HRIR was augmented with a band-pass filter that transmitted reflected solar radiation in the 0.7 µm to 1.3 µm region. The change-over from nighttime to daytime operation was accomplished by actuating a relay, either automatically or by ground station command, to insert the filter into the optical path.
For all three missions, the scan mirror was inclined to 45 degrees with a scan rate of 44.7 revolutions per minute. The Instantaneous field of view was 8.8 milliradians and the scan line separation was 8.3 km. The radiometer's instantaneous field of view covered roughly 0.5 degrees, which at an altitude of 1100 km corresponded to a ground resolution of approximately 8 km at nadir.
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.
DOCUMENT CREATION DATE