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Data Set ID:
NSIDC-0026

AVHRR Leads-ARI Polar Gridded Brightness Temperatures, Version 1

This data set consists of AVHRR imagery selected from hard copy 'quick
look' images to provide the best coverage possible over the Arctic
approximately every three days for a three-year period. Level-1B data
from NOAA/SDSD have been calibrated and mapped to earth locations,
then gridded to 1 km pixels on a basin scale to the polar stereographic
projection. The projection is similar to that used by NSIDC to produce
DMSP SSM/I polar brightness temperature and sea ice products. Each
image was ranked for areal coverage of particular seas and for degree
of cloud coverage. Passes covering a large area are generally favored over shorter passes with less cloud cover. The data set was developed
in support of the Office Of Naval Research Arctic Leads Accelerated
Research Initiative (Arctic Leads ARI). The aim of the Initiative was
to develop a more thorough understanding of the oceanography,
meteorology, and ice dynamics surrounding formation and evolution of
leads in sea ice. The leads ARI field experiment took place from March
to April 1992.

A spreadsheet containing the image rankings is available in hard copy
(NOARL Tech. Note 118, April 1991); paper copies of the spreadsheet
are available on request. Data set information is available
on-line. Data are available via FTP.

Geographic Coverage

Parameter(s):
  • Atmospheric Radiation > Albedo
  • Snow/Ice > Albedo
  • Infrared Wavelengths > Brightness Temperature
  • Sea Ice > Leads
  • Sea Ice > Reflectance
Spatial Coverage:
  • N: 90, S: 60, E: 180, W: -180

Spatial Resolution: Not Specified
Temporal Coverage:
  • 1 January 1988 to 31 December 1989
Temporal Resolution: Not specified
Data Format(s):
  • IMG
Platform(s) NOAA-10, NOAA-11, NOAA-8, NOAA-9
Sensor(s): AVHRR
Version: V1
Data Contributor(s): Florence Fetterer
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.

Fetterer, F., and J. Hawkins 2003. AVHRR Leads-ARI Polar Gridded Brightness Temperatures, Version 1. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: http://dx.doi.org/10.5067/UEMKN8TUNYKI. [Date Accessed].

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Data Set Identification

AVHRR Leads-ARI Polar Gridded Brightness Temperatures

Data Set Introduction

Although leads comprise only one percent of the surface area of the arctic ice pack, they contribute as much as half of the heat and moisture exchange at the surface during the winter. Formed as a result of ice pack deformation, leads grow anywhere from a few meters to a few kilometers wide. The fluxes generated by leads influence the atmosphere by:

  • Increasing sensible heat, thus raising the mean air temperature
  • Contributing water vapor, thus encouraging fog and cloud formation that may perturb the net radiation balance in precipitation
  • Providing buoyancy, thus producing turbulent kinetic energy for mixing

Refer to Wolfe et al. (1993) for more information. 

Using hard copies of AVHRR images provided by the Joint Ice Center (now the National Ice Center), the investigators evaluated image data for a given satellite pass, ranked each image for areal and cloud coverage, and compiled the image evaluations in monthly spreadsheets. The investigators then used the image evaluation spreadsheets to select digital imagery from the Satellite Data Services Division (SDSD) of NOAA's National Environmental Satellite Data and Information Service (NESDIS).

To facilitate comparisons of SSM/I and AVHRR data, the selected imagery was warped to the same projection and aligned with the same grid as that used by NSIDC for arctic SSM/I brightness temperature data. The projection is polar stereographic with the map plane at 70 degrees north. Two grids were used to cover most of the Arctic. The raw data were converted to albedo and brightness temperature following procedures similar to those outlined in Kidwell (1986) and Lauritson et al. (1979).

The AVHRR Leads-ARI Polar Gridded Brightness Temperatures data set consists of imagery for 1988, 1989 and 1992. The grids completely cover the Beaufort, Chukchi, East Siberian, Barents, and Kara Seas, and partially covers the East Greenland and Laptev Seas. The data set consists of image files containing the satellite data, graphics files containing the coastline overlays used with the satellite data, browse images containing subsampled images, and data files with nadir track positions.

Detailed Data Description

The AVHRR Leads-ARI Polar Gridded Brightness Temperatures data set contains Advanced Very High Resolution Radiometer images for use by scientists interested in lead dynamics and global climate change. The data set consists of AVHRR images compiled as part of the Arctic Leads Accelerated Research Initiative (Arctic Leads ARI). The data set includes images for three years for the Beaufort, Chukchi, East Siberian, Barents, Kara, East Greenland, and Laptev Seas.

Quick-look, hard copies provided by the National Ice Center of AVHRR images were used to select images for inclusion in the data set. Raw digital data for the selected images were converted to albedo and brightness temperature, and the compiled data were gridded to a stereographic projection. The data set primarily consists of image files and graphics files. It also includes browse images and files with satellite nadir track positions. Data are available via FTP.

The Arctic Leads ARI data set project was supported by the Office of Naval Research (ONR) under Program Element No. 61153N with Dr. Thomas Curtin as Program Manager. Distribution of the data set is supported by NASA under its Earth Observing System Data and Information System (EOSDIS) program. For more information about the data set, please contact NSIDC User Services.

For more information, please refer to the Arctic Leads ARI Project Description section and Instrument and Platform section.

Format

Data Granularity

A data granule is the smallest aggregation of data that can be independently described, inventoried, or retrieved. An individual image constitutes a granule in the AVHRR Leads-ARI Polar Gridded Brightness Temperatures data set.

Data Format

The data set consists of compressed UNIX files including image files, graphics files, binary nadir track files, orbital element ASCII data files, and browse image files.

The image files contain the AVHRR satellite data. Each displayable file created on the I2S system has the extension .img. The images are raw binary files of short integer data and are 2250 x 2800 pixels in size. Image files were written in sample, line, and band format, although each band of the AVHRR data is given a separate file. At NSIDC, a VAX system and VAX DIGITAL Command Language backup command were used to write files from the NOARL system to 6250 bpi tapes for NSIDC.

Please refer to the list of graphics files and sample image files. The file naming convention is illustrated by file p13jan89_2124_c1s.img as follows:

	channel 1 of an image taken	(p13jan89_2124_c1s.img)
	January 13, 1989 at 2124 GMT	(p13jan89_2124_c1s.img)
	and mapped to the Pacific Grid 	(p13jan89_2124_c1s.img)
	for short integer data		(p13jan89_2124_c1s.img)
 

The graphics files contain the WDB and WVS coastline overlays. The graphics files are full resolution (2250 x 2800 pixels) and are named as follows:

	Contents		European grid	Pacific grid

	------------------------------------------------------

	latitude/longitude	egrid.img	pgrid.img

	coastline overlays	emap.img	pmap.img

	land masks		emask.img	pmask.img

For most image files, there are corresponding nadir track files (for example, e06jan89_0913_trk.image) that contain a plot of the nadir track for the given image. An orbital element data file contains tracking information about the satellite pass during which the imagery was acquired, along with nadir track positions every ten seconds. Refer to the sample orbital element data file for more information. 

The data set also includes selected browse image files for selected 1989 AVHRR scenes. The browse images, which are in Hierarchical Data Format (HDF), are intended to provide potential data set users with information about AVHRR scenes prior to making a data request. The browse images illustrate each scene's area of coverage, highlight leads within the scene, and provide initial estimates of geophysical parameters (e.g., albedo or brightness temperature). Each browse image provides an easily-distributed scene derived from the image data and requires minimal manipulation of the raw sensor values.

The browse images are derived from original data from 1989. All browse images are 450 x 560 pixels and 8-bit per pixel. Except for the summer season when melt degrades the ability of the thermal channel to discriminate leads, the browse images are from channel 4 of the AVHRR. For the summer season, the images are from channel 2 (near-infrared). The "summer" set includes images from May, June, July, and August. Browse images from all other months are referred to as "winter" images. The archive consists of four subsets of the original data:

  • Pacific grid - summer
  • Pacific grid - winter
  • European grid - summer
  • European grid - winter

A detailed description of the data processing involved in the derivation of the browse images is available. An alphabetical list of all data set files in the AVHRR Leads-ARI Polar Gridded Brightness Temperatures data set is also available.

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Spatial Coverage

The data set covers the Beaufort, Chukchi, East Siberian, Barents, and Kara Seas, and some of the East Greenland and Laptev Seas.

grids map

Spatial Resolution

Because the sensor response is not linear with temperature, its resolution varies with channel and the temperature of the observed scene. At an altitude of 833 km and with an IFOV of 1.4 milliradians, the nominal AVHRR sensor resolution is 1.1 km at nadir and about four km at the scan limbs (at a satellite scan angle of 55.4 degrees from nadir). There are 2048 samples from each channel across each scan. The sensor swath width is about 2900 km, or 26 degrees of latitude. Data are recorded with 10-bit precision. The radiometer is operable between approximately -80 degrees C to 40 degrees C. The brightness temperature resolution of the instrument varies with temperature and is about .12 degrees C.

Projection 

Imagery was warped to a ground-plane projection using position tie points embedded in the scan lines of the Level 1B data. Tie points were calculated using Brouwer mean orbital elements from orbital information provided by the North American Air Defense Command (NORAD). Tie point accuracy depended on factors such as satellite tracking accuracy, length of time since an update, and the satellite clock accuracy. To improve the navigational accuracy given by the NESDIS tie points, each image was displayed with a graphic overlay of the coastline. For the images from 1988 and 1989, the overlay from the World Data Bank (WDB) II was used. For the 1992 images, the World Vector Shoreline (WVS) data base was used. If any coastline visible in the image did not match the graphic display, the image was shifted to make the best possible match. Often a perfect match was not possible everywhere. This was especially true along the north coast of Greenland, where the WVS is itself in error by several kilometers.

Grid Description 

To facilitate comparisons of SSM/I and AVHRR data, the Arctic Leads ARI imagery was warped to the same projection and aligned with the same grid as that used by NSIDC for arctic SSM/I brightness temperature data. The investigators considered grids with other projections including the Fleet Numerical Meteorology and Oceanography Center (FNMOC) atmospheric fields and Polar Ice Prediction System (PIPS) ice forecasts, which are available on grids with a polar projection true at 60 degrees north. They decided, however, that these and other grids were relatively coarse in comparison with the SSM/I grid.

The projection is polar stereographic with the map plane at 70 degrees north. Distortion at the pole is three percent. The north polar SSM/I grid is aligned with the SSM/I grid and covers most of the Arctic with AVHRR data. Of the two grids depicted in the Pacific and European Grids Map, the Pacific grid covers the Beaufort, Chukchi, and East Siberian Seas while the European grid covers the Barents, Kara, and some of the East Greenland and Laptev Seas. The investigators decided that increasing the coverage of the Barents Sea was preferable to covering all of the Laptev. Because very few Laptev Sea images were available and the grid size was already cumbersome in terms of data storage requirements, the investigators rejected the option of enlarging the grid to cover Laptev.

The Pacific and European grids are each 2250 x 2800 pixels. The pixel size is one km. There is a pixel border at 135 west on the Pacific grid and one at 45 degrees east on the European grid. These correspond to the alignment of cells in the SSM/I grid. Therefore, 25 x 25 AVHRR pixels will fit within each of the 25-km SSM/I grid cells. Refer to the figure that depicts the relationship between SSM/I grid coordinates and Arctic Lead ARI grid sample, line indexes.

Two coordinates conversion programs are available:

  • Program I converts from pixel sample and line indexes to polar stereographic SSM/I grid coordinates to latitude and longitude coordinates

  • Program II converts from latitude and longitude coordinates to polar stereographic SSM/I grid coordinates to pixel sample and indexes.

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Temporal Coverage

The data set consists of imagery for all months of 1989 and 1992, and all months of 1988 except February, March and May. For 1988, coverage is limited and there are no images for February, March or May. For 1989, Beaufort Sea and Chukchi Sea coverage is good except in the cloudiest month of August when Kara Sea and Barents Sea coverage is scant. For 1992, coverage in March, August, September and October is scant, with four or fewer images each month.

Temporal Resolution

The data set includes approximately 10 to 20 images per month. For 1988 and 1992, the data set includes approximately 10 images per month while for 1989, there are about 20 images per month. However, some months have many more than the average, and some have many fewer.

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Parameter or Variable

The data set consists of brightness temperature and albedo data. The parameters measured during the Arctic Leads ARI field experiment (LeadEx) in the Beaufort Sea in the spring of 1992 are identified in a list of LeadEx Instruments and Parameters.

Unit of Measurement

Brightness temperature data are presented in degrees Celsius, and albedo is presented as percent albedo.

Data Source

AVHRR data in the data set were retrieved from digital tape archived by Satellite Data Services Division (SDSD) of the NOAA National Environmental Satellite Data and Information Service (NESDIS) in Camp Springs, Maryland.

Sample Data Record

A sample data record of raw binary data is too large to present here. Please refer to the data format section for information about the contents of the images files and the availability of browse images. The following is a very small subsample of an AVHRR image from the data set showing a large lead off Banks Island.

AVHRR Image Subsample
AVHRR Image Subsample

The sample is a channel 4 image from a pass made December 14, 1989 and is a subsample of an image presented in Fetterer et al. (1993).

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Project Description

Ships and submarines have historically used leads, or sea ice fractures, to navigate Arctic waters. Scientists study leads to better understand their roles in arctic climatology and global climate change. Leads, particularly those exposing warm ocean water to cold arctic air, influence the energy balance at polar latitudes by contributing to the atmospheric heat flux. Because the poles act as heat sinks in the global energy balance, lead formation, evolution and distribution in the polar regions is important.

Satellite imagery provides invaluable views of leads to scientists interested in lead dynamics. For that reason, a data set of Advanced Very High Resolution Radiometer (AVHRR) imagery has been compiled as part of the Arctic Leads Accelerated Research Initiative ARI (Arctic Leads ARI). The Project Investigators for the Arctic Leads ARI Data Set evaluated hard copies of AVHRR imagery to select images for the data set. The raw data for selected images were converted to albedo and brightness temperature, and gridded to a stereographic projection. The data set consists of imagery for 1988, 1989, and 1992. Grids completely cover the Beaufort, Chukchi, East Siberian, Barents, and Kara Seas, and partially cover the East Greenland and Laptev Seas. The data set is available through NSIDC User Services.

For more information, please refer to the Instrument and Sensor section.

1. Project Overview

Name of Project

Office of Naval Research Arctic Leads Accelerated Research Initiative (ARI)

Project Introduction

The objective of the Arctic Leads ARI was to gain a better understanding of lead dynamics. As part of the project, the Arctic Leads ARI Data Set was created to encourage the assembly of an arctic leads climatology. The ARI was sponsored by the Office of Naval Research (ONR) and included the LeadEx field experiment in the spring of 1992.

The Arctic Leads ARI project was supported by ONR under Program Element No. 61153N with Dr. Thomas Curtin as Program Manager. Distribution of the data set is supported by NASA under its Earth Observing System Data and Information System (EOSDIS) program. Please refer to the acknowledgements made by the Principal Investigators for the data set project.

Project Mission Objectives

The goal of the five year Arctic Leads ARI was a more thorough understanding of the oceanography, meteorology, and ice dynamics surrounding lead formation and evolution.

Disciplines

The data set is of use to scientists investigating global climate change as well as oceanographers and meteorologists studying the Arctic region. Specifically, it has applications in the following areas:

  • arctic lead statistics and climatology
  • the arctic energy budget
  • heat flux and surface flux
  • ice dynamics, leads rheology, and leads mapping
  • studies of lead parameters and measurements
  • surface temperature and albedo computations

Geographic Region

Images available for the Arctic area outlined on the Arctic Leads ARI Grid Map including the Beaufort, Chukchi, East Siberian, Barents, Kara, East Greenland, and Laptev Seas.

Detailed Project Description

In January 1989, a workshop was held at the University of Washington's Applied Physics Laboratory (UW/APL) to plan the Office of Naval Research (ONR) Arctic Leads Accelerated Research Initiative (Arctic Leads ARI). At this meeting, a Remote Sensing Working Group was formed to focus on leads issues including:

  • the relationship of lead patterns to the wind field
  • the regional distribution of lead width, orientation, and fractional area over time
  • the computation of surface fluxes over large areas.

The Remote Sensing Working Group determined that a satellite data set was needed to support the science objectives outlined in their workshop report. The AVHRR was selected for its ability to acquire data with Arctic-wide views at a resolution useful for leads statistics retrieval. In September 1989, a discussion about the type of data set needed took place at the Cooperative Institute for Research in Environmental Sciences (CIRES). This discussion resulted in a successful Naval Oceanographic and Atmospheric Research Laboratory (NOARL, now a part of the Naval Research Laboratory) proposal to ONR for the creation of an AVHRR Arctic leads data set.

In April 1990, the Remote Sensing Branch of NOARL began selecting AVHRR data from NOAA archives. Using hard copy prints from the Navy/NOAA Joint Ice Center, the investigators selected imagery in an attempt to cover most of the Arctic every three days. The selected imagery was processed on a scale that allows for the observation of regional, seasonal, and annual variability in lead patterns. The raw data for the selected images were converted to albedo and brightness temperature, and the compiled data were gridded to a stereographic projection identical to that used for Special Sensor Microwave Imager (SSM/I) data by the National Snow and Ice Data Center. The data set includes imagery for 1989 through 1991 that covers the Arctic in two grids of 1-km pixels.

The LeadEx field component of ONR's Arctic Leads ARI was carried out in March and April of 1992 in the Beaufort Sea. The effect of open leads on the polar ocean and atmosphere was studied using data collected from a base camp northeast of Prudhoe Bay, Alaska and at several nearby leads using remote and in situ, surface-based sensors.

2. Data Availability

Data Type

The data set consists of both image files and graphics files, and also includes files with satellite nadir track positions.

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Software and Tools

Software and Tools

Copies of the following coordinates conversion programs are available:

  • Program I converts from pixel sample and line indexes to polar stereographic SSM/I grid coordinates to latitude and longitude coordinates

  • Program II converts from latitude and longitude coordinates to polar stereographic SSM/I grid coordinates to pixel sample and indexes

The Cloud and Surface Parameter Retrieval (CASPR) system is a toolkit that can be used to retrieve a variety of surface and cloud parameters from AVHRR data.

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Data Acquisition and Processing

Theory of Measurements

The AVHRR is a radiometer carried aboard polar orbiting satellites. It senses and measures the intensity of passive radiant energy emitted and reflected by the Earth and its atmosphere. Hastings and Emery (1992) summarize the historical development of the AVHRR sensor hardware and provide an overview of its data collection capabilities. For more information on the theory of AVHRR measurements, please refer to the Arctic Leads ARI Instrument section.

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Data Acquisition Methods

The following description of the Arctic Leads ARI data acquisition methods are summarized from Fetterer and Hawkins (1991).

AVHRR Data Availability

AVHRR data formerly archived by the Satellite Data Services Division (SDSD) of NOAA's National Environmental Satellite Data and Information Service (NESDIS), are now archived by the Climate Services Division (CSD) of the National Climatic Data Center (NCDC) at NESDIS in Asheville, North Carolina. The data can be obtained in three forms:

  • HRPT (High Resolution Picture Transmission)
  • LAC (Local Area Coverage)
  • GAC (Global Area Coverage)

HRPT direct readout data are continuously broadcast from the satellite and are available for areas within a ground station mask. For instance, the Gilmore Creek, Alaska ground station receives HRPT data covering the Beaufort, Bering, Chukchi, and East Siberian Seas. LAC data are HRPT data that have been recorded on board the satellite for playback when the satellite is within range of a Command and Data Acquisition (CDA) station. Up to ten minutes of LAC data can be recorded during each orbit. GAC data are reduced resolution data acquired during an entire orbit and stored for playback on command. A resolution cell size of about four km at nadir makes GAC unsuitable for most Arctic Leads ARI purposes.

Image Evaluation and Selection

Hard copy prints of the AVHRR imagery were usually made using channel 4 (IR) during the arctic winter and channel 2 (visible) in summer. When the investigators visited SDSD in March 1990, they found the hard copy archive to be of limited use because it contained very few LAC and HRPT hard copies and no latitude/longitude grids. As an alternative to the SDSD archive, the investigators used an archive of hard copy AVHRR images at the Navy/NOAA Joint Ice Center (now the National Ice Center), which uses AVHRR as a primary tool for ice analysis and forecasting and makes a hard copy of almost every HRPT and LAC pass.

Images are from one to three frames long. Each frame includes about three minutes of data covering about nine degrees of latitude. An ascending pass starting at 70 degrees over Alaska would cover just the Beaufort Sea if the resulting image were only one frame long. If the image were three frames in length, the same pass would cover the Beaufort, Chukchi, East Siberian, Laptev, and some of the central Arctic.

Using the hard copies provided by the Joint Ice Center, image data for a given satellite pass were evaluated to determine how much of each sea was covered by the pass and how much of the image was covered by clouds. The investigators examined all images but eliminated from consideration images that were clearly of no value to the Arctic Leads ARI. The investigators noted the time and orbit printed on each hard copy as well as the seas covered by the image. They then ranked each image on a scale of one to five for degree of cloud cover and areal coverage. For example, a rank of "5-2" for the Beaufort Sea would mean that 100 percent of the image is cloud-free but only about 40 percent of the Beaufort is covered by the image.

The investigators then compiled their image evaluations in monthly spreadsheets, which they used to select imagery for inclusion in the data set. Early evaluations revealed a need to change the original data selection goals of 20 images per month and complete coverage of the Arctic every three days. Limited areal coverage outside the Beaufort Sea and extensive cloud cover as well as budgetary limitations mandated the change. Initially, the investigators selected images in an attempt to cover the entire Arctic with evenly spaced temporal intervals. After recognizing the extent of could cover in the images, they elected to take advantage of the available data by selecting approximately 10 images of leads per month representing several sequential cloud free days. Unless shorter passes were part of time sequences in which leads could clearly be seen, the investigators generally favored passes covering large areas over shorter, relatively cloud free passes.

Observations

Data Notes

This field is intentionally left blank.

Field Notes

The Arctic Leads ARI included a field experiment (LeadEx) in the Beaufort Sea to study the effect of open leads on the polar ocean and atmosphere. During March and April of 1992, data were collected from a base camp northeast of Prudhoe Bay, Alaska and at several nearby leads using remote and surface based sensors. A list of LeadEx Instruments and Parameters identifies the meteorological instruments used and parameters measured during the LeadEx field operations.

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Derivation Techniques and Algorithms

For the full resolution images, the raw data were converted to albedo and brightness temperature following procedures similar to those outlined in Kidwell (1986) and Lauritson et al. (1979).

Processing Steps

Data from channels 1 and 2 were processed by converting raw counts to albedo using a straight line approximation based on pre-launch calibration. Albedo was expressed as a percentage of that for a perfectly reflecting Lambertian surface illuminated by an overhead sun. Each output count in the processed data was 0.1 percent. For example a count of 500 would equal 50 percent albedo.

Raw count values for channels 3, 4, and 5 were converted to radiances using a straight line approximation to calibration from onboard observations of space and an internal blackbody. Each possible raw count value of zero to 1023 on the NOAA Level-1B data tape was matched with a radiant energy value in a look-up table. Energy was then converted to brightness temperature based on the inverse of Plank's function.

Data processing steps are described in detail in Fetterer and Hawkins (1993).

Processing Changes

This section is not relevant to this document and is intentionally left blank.

Calculations

Brightness temperatures were converted to output counts using the equation:

N = (10(K-273.16)) + 500, where:
N = output count value
K = brightness temperature (degrees Kelvin)

Output count values are stored in short integer (16-bit) form. Count values can be converted to degrees Kelvin using:

K = ((N-500)/10) + 273.16

or to degrees Celsius using:

C = (N-500)/10

The result is 0.1 degree per count, with a count of 500 equal to 0 degrees C. If the temperature observed is less than -50 degrees C, the count value will be negative.

NOTE: If the count values of 16-bit processed imagery are to be displayed using hardware with an 8-bit deep image plane, the 16-bit images must be scaled to 8-bit images.

Special Corrections/Adjustments

For channels 1 and 2, no corrections were made for sun angle or atmospheric effects. A nonlinear correction to temperature was applied to channels 3, 4, and 5 using the coefficients for each channel given in periodic NOAA updates and Lauritson et al. (1979).

The program that created the nadir track listings was modified so that a nadir track could be created even if it fell outside the image.

Calculated Variables

The raw data were converted to albedo and brightness temperature using the methods described above.

Graphs and Plots

A detailed description of the data processing involved in the derivation of the browse images is available.

Error Sources

More information about the quality of the data set imagery is available in Fetterer and Hawkins (1993).

Notes 

Because relatively cloud free images were selected for the data set, it is not particularly well suited for cloud studies. For 1988, coverage is limited and there are no images for February, March or May.

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Sensor or Instrument Description

The AVHRR sensor is a broad band, cross-track scanning instrument that senses in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum. Depending on the model, the AVHRR is a four or five channel scanner. It has flown continuously on the NOAA polar orbiting series of satellites since 1978 and provides pole-to-pole on board collection of data from all channels. The satellite orbits the Earth approximately 14 times per day at an orbital inclination of about nine degrees. Each pass covers a 2399-km wide swath. 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.

A table listing the wavelengths of each of the AVHRR channels is available. Another table identifies the NOAA satellites that carried the AVHRR during the period of interest to the Leads ARI. 

Platform Description

In TIROS-N Source/Platform Document (NOAA POES), the NOAA Satellite Active Archive DAAC describes the NOAA Polar Orbiting Environmental Satellites (POES) that carried the AVHRR instrument.

Instrument Descriptions

The Goddard Space Flight Center DAAC describes the AVHRR instrument in:

  • the equipment section of the NOAA/NASA Pathfinder Data Set Guide Document for the AVHRR Land Data Sets

Additionally, the United States Geological Survey (USGS) describes the AVHRR instrument in the following:

  • Advanced Very High Resolution Radiometer document
  • AVHRR Sensor Characteristics section of its Global Land 1-KM AVHRR Data Set Project Guide Document.
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Application of the Data Set

The relevance of ice lead width and width distribution to flux calculations in sea ice and climate models has been addressed (Maslanik and Key 1995) and AVHRR imagery has been used to study lead pattern formation in the Beaufort Sea in response to wind forcing (Walter and Overland 1993)Lindsay and Rothrock (1994) used the AVHRR Leads-ARI Polar Gridded Brightness Temperatures data set to estimate the surface temperature of arctic sea ice. Lindsay and Rothrock (1995) derived lead orientation and width statistics with the data set. The data set could also be used to:

  • Develop algorithms for the automatic derivation of lead statistics
  • Assemble an arctic leads climatology using the lead statistics algorithms
  • Study the relationship between the arctic energy budget and heat flux through leads
  • Estimate the importance of leads in humidifying polar air masses
  • Study the effect of lead opening and closing on ice dynamics and the upper ocean
  • Map leads and reveal ice rheology through lead patterns
  • Calculate lead widths, width distributions, lead lengths, lead orientations, and open water areas and fractions
  • Calculate surface fluxes using lead width, density, orientation and other lead parameters
  • Summarize surface temperature and albedo
  • Make navigation plans for ships and submarines

Hastings and Emery (1992) provide an overview of general AVHRR data applications.

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References and Related Publications

Contacts and Acknowledgments

Investigators' Names and Titles

The Principal Investigators for the data set project of the Arctic Leads ARI were:

Florence M. Fetterer, National Snow and Ice Data Center

Jeffrey D. Hawkins, Meteorologist, Prediction Systems Branch, Naval Research Laboratory, Marine Meteorology Division

Title of Investigation

AVHRR Leads-ARI Polar Gridded Brightness Temperatures. For a description of the Arctic Leads Accelerated Research Initiative (ARI), please see the Project Description guide document.

Acknowledgments: 

The Principal Investigators would like to acknowledge:

  • Duane Eppler, Denny Farmer, Jeff Key, Ron Lindsay, Jim Maslanik, Drew Rothrock, Axel Schweiger, Bernard Walter, and Ron Weaver, all of whom offered valuable suggestions for the construction of the data set
  • Bobby Grant of Sverdrup Technology for capably processing the AVHRR data
  • Rich Goldcamp, also of Sverdrup Technology, for providing programming support
  • Dave Benner and Cheryl Bertoia of the National Ice Center (formerly the Navy/NOAA Joint Ice Center) for providing hard copy imagery

Document Information

DOCUMENT CREATION DATE

31 August 1995

DOCUMENT REVISION DATE

24 October 2011

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NSIDC User Services
Phone: 1 303 492-6199
Email: nsidc@nsidc.org