4 km AVHRR Pathfinder v5.0 Global Day-Night Sea Surface Temperature Averages, 1985-2009 (NODC Accession 0077816)

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Frequently anticipated questions:


What does this data set describe?

Title:
4 km AVHRR Pathfinder v5.0 Global Day-Night Sea Surface Temperature Averages, 1985-2009 (NODC Accession 0077816)
Abstract:
This data set contains a set of monthly and yearly global day-night sea surface temperature averages, derived from the AVHRR Pathfinder Version 5 sea surface temperature cloudscreened data set (<http://pathfinder.nodc.noaa.gov>) in GeoTIFF format. The AVHRR Pathfinder SST data sets provide the longest, most accurate, and highest resolution consistently-reprocessed SST climate data record from the AVHRR sensor series. These day-night combined monthly and yearly means were produced from cloud-screened day-night monthly full resolution files of Pathfinder SST data from 1985-2009. The data are available for download at <http://accession.nodc.noaa.gov/0077816> or through the NODC Geoportal at <http://data.nodc.noaa.gov/geoportal/>. The original .HDF files are archived at the National Oceanographic Data Center under separate accession numbers. The GeoTIFF SST averages were assigned projection GCS_WGS_1984. In addition, browse images in .png format with an associated .kml file for each year are included with these data as well as detailed metadata.
Supplemental_Information:
A land mask is not included with these data. The NODC does not routinely provide land masks in its products. A suggested shoreline is the Global Self-consistent Hierarchical High-resolution Shoreline Database (GSHHS) available at <http://www.ngdc.noaa.gov/mgg/shorelines/gshhs.html> and <http://www.soest.hawaii.edu/pwessel/gshhs/index.html> (Wessel, P., and W. H. F. Smith, A Global Self-consistent, Hierarchical, High-resolution Shoreline Database, J. Geophys. Res., 101, 8741-8743, 1996.)

During the averaging process, NODATA pixels were not included; data pixels with no corresponding data pixels were maintained as their original number to maximize the amount of available data. The complete product development process is available at <http://www.nodc.noaa.gov/SatelliteData/pathfinder4km/PFV5_GIS_tutorial.html>.

The NODC collection of value-added, cloud-screened products in HDF4 were developed from original AVHRR Pathfinder files archived at the NODC. These products contain daytime, nighttime, and day-night averaged data of quality flags 4-7, as well as standard deviation and pixel count information. They have been produced from the original Pathfinder Version 5.0 data by NODC for Daily, 5-day, 7-day, and monthly temporal averages at 4km and one degree spatial resolution, as well as five degree spatial resolution for monthly products. The monthly full resolution products were utilized to develop the final GIS files of this data set. While these cloudscreened files are derived from official Pathfinder Version 5.0 data, they are NOT part of the official NODC Version 5.0 collection. To access this collection use the Version5.0/ directory at the NODC's Pathfinder section of the website. For more information on their provenance, contents, or relationship to official Pathfinder Version 5.0 data, please contact Ken Casey at Kenneth.Casey@noaa.gov. NODC December 2010

  1. How should this data set be cited?

    NOAA National Oceanographic Data Center (NOAA/NODC), 20110902, 4 km AVHRR Pathfinder v5.0 Global Day-Night Sea Surface Temperature Averages, 1985-2009 (NODC Accession 0077816): NOAA National Oceanographic Data Center, Silver Spring, MD U.S.A..

    Online Links:

    Other_Citation_Details:
    These SST averages were produced from monthly cloud-screened day-night averages of Pathfinder v5 SST data from 1985-2009, which are archived at the National Oceanographic Data Center.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -180.0
    East_Bounding_Coordinate: 180.0
    North_Bounding_Coordinate: 90.0
    South_Bounding_Coordinate: -90.0

  3. What does it look like?

    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1985/browse/1985_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1985 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1986/browse/1986_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1986 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1987/browse/1987_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1987 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1988/browse/1988_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1988 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1989/browse/1989_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1989 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1990/browse/1990_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1990 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1991/browse/1991_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1991 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1992/browse/1992_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1992 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1993/browse/1993_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1993 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1994/browse/1994_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1994 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1995/browse/1995_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1995 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1996/browse/1996_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1996 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1997/browse/1997_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1997 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1998/browse/1998_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1998 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/1999/browse/1999_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 1999 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2000/browse/2000_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2000 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2001/browse/2001_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2001 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2002/browse/2002_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2002 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2003/browse/2003_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2003 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2004/browse/2004_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2004 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2005/browse/2005_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2005 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2006/browse/2006_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2006 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2007/browse/2007_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2007 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2008/browse/2008_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2008 from Pathfinder v5 day/night full resolution cloudscreened files.
    <http://data.nodc.noaa.gov/nodc/archive/data/0077816/2009/browse/2009_Pathv5.0_daynight_SST_meanc1.png> (PNG)
    Browse image of global average yearly sea surface temperatures for 2009 from Pathfinder v5 day/night full resolution cloudscreened files.

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 01-Jan-1985
    Beginning_Time: Unknown
    Ending_Date: 31-Dec-2009
    Ending_Time: Unknown
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: data files

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      Indirect_Spatial_Reference:
      Global sea surface temperature values (-180 to 180 and -90 to 90 longitude and latitude)
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 4096 x 8192, type Pixel

    2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest .0439. Longitudes are given to the nearest .0439. Latitude and longitude values are specified in Decimal Degrees.

      The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.

  7. How does the data set describe geographic features?

    Pathfinder Version 5.0 SST Data
    Temporal averages of SST data (monthly and yearly) (Source: NOAA National Oceanographic Data Center/Satellite Oceanography Group)

    All Pixel Sea Surface Temperature (SST)
    The all-pixel SST files contain values for each pixel location, including those contaminated with clouds or other sources of error. The Overall Quality Flag values (4-7) may be used to filter out these unwanted values. The SST value in each pixel location is an average of the highest quality AVHRR Global Area Coverage (GAC) observations available in each roughly 4 km bin. SST is a difficult parameter to define exactly because the upper ocean (~10 m) has a complex and variable vertical temperature structure that is related to ocean turbulence and the air-sea fluxes of heat, moisture and momentum. Definitions of SST provide a necessary theoretical framework that can be used to understand the information content and relationships between measurements of SST made by different instruments. The following explanatory statements attempt to provide this framework and encapsulate the effects of the dominant heat transport processes and time scale of variability associated with distinct vertical and volume regimes within a vertical element of the water column (horizontal and temporal variability is implicitly assumed): -The interface SST, SSTint, is the temperature of an infinitely thin layer at the exact air-sea interface. It represents the temperature at the top of the SSTskin temperature gradient (layer) and cannot be measured using current technology. It is important to note that it is the SSTint that interacts with the atmosphere. -The skin SST, SSTskin, is a temperature measured within a thin water layer (<500 micrometer) adjacent to the air-sea interface. It is where conductive, diffusive and molecular heat transfer processes dominate. A strong vertical temperature gradient is characteristically maintained in this thin layer sustained by the magnitude and direction of the ocean-atmosphere heat flux. Thus, SSTskin varies according to the actual measurement depth within the layer. This layer provides the connectivity between (Source: Modified from <http://podaac.jpl.nasa.gov/ghrsst/SST-definitions.html>)

    ValueDefinition
    sea surface temperatureThe .HDF files are 16-bit files, and pixel values can range from 0 to 65535 (2 to the 16th power). However, realistic pixel values for SST will always be less than 600 or so. SST in degrees C = (0.075 * pixel value) - 3.0, so a pixel value of 600 equals 42 degrees C, a temperature which exceeds normal SST limits. Temperatures are represented in 0.075 degree C increments

    Entity_and_Attribute_Overview:
    AVHRR Pathfinder v5 monthly and yearly means of day-night combined sea surface temperatures in GIS-ready format (developed from Pathfinder v5 day-night cloudscreened files, quality level 4-7)
    Entity_and_Attribute_Detail_Citation:
    NOAA National Oceanographic Data Center/Satellite Oceanography Group


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

    Sheri Phillips, Yuanjie Li, Upendra Dadi, and Tess Brandon, NOAA National Oceanographic Data Center

  3. To whom should users address questions about the data?

    NOAA National Oceanographic Data Center
    Attn: Sheri Phillips
    SSMC 3, 4th Floor, E/OC1
    Silver Spring, MD 20910
    USA

    301-713-3277 (voice)
    301-713-3302 (FAX)
    NODC.Services@noaa.gov

    Hours_of_Service: 9-5:00 PM, EST
    Contact_Instructions: Phone, FAX, Letter, E-mail during normal business hours


Why was the data set created?

These data files were produced to facilitate the utilization of high resolution Pathfinder v5 sea surface temperature data within geographic information system (GIS)software.


How was the data set created?

  1. From what previous works were the data drawn?

    Pathfinder v5 monthly cloudscreened files (source 1 of 1)
    NOAA National Oceanographic Data Center, 20110422, Pathfinder v5.0 Cloudscreened data product files: NOAA National Oceanographic Data Center, Silver Spring, MD.

    Online Links:

    Other_Citation_Details:
    The AVHRR Pathfinder data files are a collection of value-added, cloud-screened products in HDF4. These products contain daytime, nighttime, and day-night averaged data of quality flags 4-7 only, as well as standard deviation and pixel count information. They have been produced from the original Pathfinder Version 5.0 data by NODC for Daily, 5-day, 7-day, and monthly temporal averages at 4km and one degree spatial resolution, as well as five degree spatial resolution for monthly products. While these files are derived from official Pathfinder Version 5.0 data, they are NOT part of the official NODC Pathfinder Version 5.0 collection. To access this collection use the Version5.0/directory at NODC's online Pathfinder pages For more information on their provenance, contents, or relationship to official Pathfinder Version 5.0 data, please contact Ken Casey at Kenneth.Casey@noaa.gov. NODC December 2010
    Type_of_Source_Media: data files
    Source_Scale_Denominator: 5
    Source_Contribution:
    Monthly and yearly GIS-format SST averages were developed from the AVHRR Pathfinder v5 cloudscreened day-night monthly files.

  2. How were the data generated, processed, and modified?

    Date: 08-Apr-2011 (process 1 of 1)
    The SST averages were developed within ESRI Corporation ArcGIS v10.0 software in combination with the ArcGIS Spatial Analyst Tool. Basic procedure - 1) Obtain 12 months of Pathfinder yearly cloudscreened files for a given year. For each month: 2) In GIS, run histogram for each layer month 3) Assign null value (NODATA) to 0 (land) via SETNULL, RASTER CALCULATOR, or reclassification for each layer month (e.g, pixel values less than 15 are assigned NODATA). 4) Use RASTER CALCULATOR to convert pixel values for each month to degrees C (Raster *.075 -3). 5) Use LOCAL CELL STATISTICS TOOL to compute average for the 12 month period. During the averaging process, NODATA pixels were not included; data pixels with no corresponding data pixels were maintained as their original number to maximize the amount of available data. The complete product development process is available at <http://www.nodc.noaa.gov/SatelliteData/pathfinder4km/PFV5_GIS_tutorial.html> and is documented in the NODC_Path5_means_methodology.pdf file. 6) Assign projection.

    Person who carried out this activity:

    NOAA National Oceanographic Data Center
    Attn: Sheri Phillips
    Oceanographer
    SSMC3, 4th Floor, E/OC1
    Silver Spring, MD 20910
    USA

    301-713-3277 (voice)
    301-713-3302 (FAX)
    NODC.Services@noaa.gov

    Hours_of_Service: 9-5:30 PM, EST
    Contact_Instructions: Phone/FAX/E-mail/letter during normal business hours
  3. What similar or related data should the user be aware of?


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

    The original .HDF files used to develop these averages are 16-bit files, and pixel values can range from 0 to 65535 (2 to the 16th power). However, realistic pixel values for SST will always be less than 600 or so. The 'calculate histogram' feature was utilized from within Arc-GIS software to establish actual pixel values for each monthly .HDF file used for each yearly average. In addition, a reclassification was performed on each monthly file to remove unrealistic pixel data values of 15 and less. 'Land' has a value of 1. SST in degC = 0.075 x pixel value - 3.

  2. How accurate are the geographic locations?

    The major sources of error in geo-locating AVHRR data are (a) drift in the spacecraft clock (which causes errors in the estimated along-track position), and (b) uncertainty errors in spacecraft and sensor attitude. (a) Clock Correction To minimize error in the along track position estimated by the orbital model, a satellite a clock correction factor is applied to the time code imbedded in each piece. The method used to determine these clock correction factors is presented below. The clock aboard a given satellite drifts continually at a relatively constant rate (e.g., for NOAA-14, ~9msday-1) compared to the reference clock on Earth. Because of this drift, the NOAA/NESDIS Satellite Operation Control Center periodically sends a command to the satellite to reset the on-board clock to a new baseline thereby eliminating the accumulation of a large time offset error between the Earth and satellite clocks. To correct for clock drift between these resets, correction factors were determined from a database of satellite clock time and Earth time offsets collected at the RSMAS High Resolution Picture Transmission (HRPT) receiving station. During HRPT transmission, both the satellite clock (used to create the embedded time code in each piece) and the Earth clock are simultaneously available. The clock correction bias was determined by (1) visual examination of the Earth/satellite clock differences collected in the database to locate the precise magnitude and timing of clock resets performed by the Satellite Operation Control Center and (2) recorded time differences between the identified reset periods were then filtered to remove spurious noise, and regressed against the corresponding satellite time to determine the clock drift correction. These drift corrections were then applied to all data time-stamped during a given reset period. Refer to Sea Surface Temperature Global Area Coverage (GAC) Processing Appendix A: Calibration and Navigation Correction Factors for a list of clock offsets for each NOAA spacecraft (<http://www.rsmas.miami.edu/groups/rrsl/pathfinder/Processing/proc_app_a.html>). (b) Attitude Corrections - After clock correction, a nominal attitude correction is then applied to minimize the uncertainty in regard to the direction in which the spacecraft is pointing. The nominal attitude correction applied was determined by averaging the absolute attitude of the spacecraft over many geographic locations and times along the orbital track. The method used to determine the absolute attitude of the spacecraft involves matching a digital coastal outline to a given image and recording the amount of pitch, yaw, and roll required to make the outline and land coincide. This method has the advantage that it can be performed over small geographical distances and is similar to other techniques which rely on widely separated geographical control points to anchor the navigation. The resultant navigation information, output by the SECTOR procedure for each piece, provides the mapping parameters needed to convert between the satellite perspective of pixel and scan line, and Earth-based latitude and longitude coordinates. Refer to Sea Surface Temperature Global Area Coverage (GAC) Processing Appendix A: Calibration and Navigation Correction Factors for attitude correction factors for each NOAA spacecraft (<http://www.rsmas.miami.edu/groups/rrsl/pathfinder/Processing/proc_app_a.html>).

  3. How accurate are the heights or depths?

    Refer to the Horizontal Positional Accuracy Report of this metadata record for a discussion of sources of error in geo-locating AVHRR data.

  4. Where are the gaps in the data? What is missing?

    A reclassification was performed utilizing GIS software against each monthly .HDF file used in producing each yearly average to remove artifact pixel values of 15 and less.

  5. How consistent are the relationships among the observations, including topology?

    Files were visually inspected to ensure a valid sea surface temperature range and distribution. As an additional spot-check, for several years, files were then compared against annual averages calculated in Matlab. Differences between GIS- and Matlab-derived annual averages were found to be negligible, and could be attributed to rounding error.


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:
Please acknowledge the use of these data with - The Pathfinder Version 5 SST Data were provided by the NOAA/National Oceanographic Data Center at URL: <http://pathfinder.nodc.noaa.gov>

  1. Who distributes the data set? (Distributor 1 of 1)

    NOAA National Oceanographic Data Center
    Attn: NODC User Services
    NOAA/NESDIS E/OC1
    Silver Spring, MD 20910-3282
    USA

    301-713-3277 (voice)
    301-713-3302 (FAX)
    NODC.Services@noaa.gov

    Hours_of_Service: 9-5:30 PM, EST
    Contact_Instructions: Phone/FAX/E-mail/Letter during regular business hours
  2. What's the catalog number I need to order this data set?

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

    NOAA makes no warranty regarding these data, expressed or implied, nor does the fact of distribution constitute such a warranty. NOAA and NODC cannot assume liability for any damages caused by any errors or omissions in these data, nor as a result of the failure of these data to function on a particular system.

  4. How can I download or order the data?

  5. Is there some other way to get the data?

    Contact the NODC User Services Group via phone/FAX/E-mail: nodc.services@noaa.gov

  6. What hardware or software do I need in order to use the data set?

    PC, Mac, UNIX or other, standard Internet browser, ability to work with/utilize GIS files strongly recommended, knowledge of satellite data products


Who wrote the metadata?

Dates:
Last modified: 28-Dec-2012
Last Reviewed: 02-May-2012
To be reviewed: 30-Jul-2012
Metadata author:
NOAA National Oceanographic Data Center
Attn: Sheri Phillips
oceanographer
SSMC3, 4th Floor, E/OC1
Silver Spring, Maryland 20910
USA

301-713-3280 x127 (voice)
301-713-3302 (FAX)
sheri.phillips@noaa.gov

Hours_of_Service: 10-6:30 PM, EST
Contact_Instructions: Phone, E-mail, letter at address listed in this metadata record
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)


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