The Advanced Very High Resolution Radiometer (AVHRR) data set is comprised of data collected by National Oceanic and Atmospheric Administration (NOAA) AVHRR sensors and held in the archives of the International Observatory of the North (ION) at the University of Alaska Fairbanks (UAF). Carried aboard the National Oceanic and Atmospheric Administration's Polar Orbiting Environmental Satellite series, the AVHRR sensor is a broad-band, 4- or 5-channel scanning radiometer, sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum. ION houses AVHRR High Resolution Picture Transmission (HRPT) data and Local Area Coverage (LAC) data. The HRPT data are full resolution image data transmitted to a ground station as they are collected, while LAC data (also full resolution data) are recorded with an onboard tape recorder for subsequent transmission during a station overpass. The objective of the AVHRR instrument is to provide radiance data for investigation of clouds, land-water boundaries, snow and ice extent, ice or snow melt inception, day and night cloud distribution, temperatures of radiating surfaces, and sea surface temperature. AVHRR data in the Visible and thermal-IR channels allow for discrimination between young and old ice which is important for lead detection. The average instantaneous field-of-view (IFOV) of 1.4 milliradians yields a LAC/HRPT ground resolution of approximately 1.1 km at the satellite nadir from the nominal orbit altitude of 833 km (517 mi).
These satellite data were acquired and processed by the University of Alaska Fairbanks to meet contract requirements for the US Mineral Management Service: Mapping and Characterization of Recurring Spring Leads and Landfast ice in the Beaufort and Chukchi Seas (AK-03-06).
For the purposes of the MMS study, the file names associated with Band 1 data (visual) are prefixed with a "v" and Band 4 files (thermal) prefixed with a "t". The day of the year, hour and minutes are incorporated in the file names. For descriptive purposes the following abbreviations are used as placeholders for real values to illustrate the naming convention: d = day of year Y = Year T = time in GMT A Band 1 image follows this convention: v d d d _T T T T.tif A Band 4 image follows this convention: t d d d _T T T T.tif Examples of these file names are v015_1012.tif and t015_1012.tif
Any hardcopies or published datasets utilizing these data sets shall clearly indicate their source. If the user has modified the data in any way they are obligated to describe the types of modifications that they have performed. User specifically agrees not to misrepresent these datasets, nor to imply that any changes that they made were approved by the University of Alaska.
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The funding for this effort was provided by the US Mineral Management Service for Mapping and Characterization of Recurring Spring Leads and Landfast ice in the Beaufort and Chukchi Seas (AK-03-06, MMS-71707)
Each file was visually checked in an image browser to confirm placement and projection definition.
ION uses satellite navigation and attitude parameters for scene navigation (with additional ground control) to produce adequate results (with errors <3 km) for geolocated AVHRR imagery.
Visual interpretation, distance measurement tools
High Resolution Picture Transmission (HRPT) data are full resolution image data transmitted to UAF's ground station at the International Observatory of the North (ION) as they are collected.
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AVHRR data was geolocated, calibrated and reprojected in GeoTIFF format using TeraScan software. A coast mask is applied in ENVI. The fraction of leads within each pixel is then determined based on the brightness temperatures or reflectances of open water and the surrounding thick ice, as described by Lindsay and Rothrock (Arctic sea ice leads from advanced very high resolution radiometer images. Journal of Geophysical Research, 100(C3), 4533-4544, 1995). Here, we have corrected for regional differences in surface temperature and reflectance as well as thin cloud cover by determining the fraction of leads within a moving 50 by 50 pixel (55 x 55 km) square window, with the fraction of thick ice based on the upper and lower quartile reflectance and brightness temperature, respectively. For a few cases of more expansive stretches of open water, manual adjustments of open water extent have been made. The resulting image indicating the fraction of open water is then binarized about a threshold corresponding to an open water fraction of 25% in each pixel, with pixels containing less open water designated as ice and those at or above 25% designated as leads. This information is then brought into NIH Image for derivation of lead location, shape and size statistics, open water fractions and other information for the different study subregions.
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AVHRR Level 1b
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