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
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:
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.
| Value | Definition |
|---|---|
| sea surface temperature | The .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 |
Sheri Phillips, Yuanjie Li, Upendra Dadi, and Tess Brandon, NOAA National Oceanographic Data Center
301-713-3277 (voice)
301-713-3302 (FAX)
NODC.Services@noaa.gov
These data files were produced to facilitate the utilization of high resolution Pathfinder v5 sea surface temperature data within geographic information system (GIS)software.
NOAA National Oceanographic Data Center, 20110422, Pathfinder v5.0 Cloudscreened data product files: NOAA National Oceanographic Data Center, Silver Spring, MD.Online Links:
Person who carried out this activity:
301-713-3277 (voice)
301-713-3302 (FAX)
NODC.Services@noaa.gov
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.
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>).
Refer to the Horizontal Positional Accuracy Report of this metadata record for a discussion of sources of error in geo-locating AVHRR data.
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.
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.
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>
301-713-3277 (voice)
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NODC.Services@noaa.gov
Downloadable Data
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.
| Data format: | Global monthly and yearly SST averages developed from Pathfinder v. 5 day-night cloudscreened full resolution data in format TIFF GeoTIFF Size: 11250.0 |
|---|---|
| Network links: |
<http://accession.nodc.noaa.gov/0077816> |
| Data format: | Browse graphics associated with corresponding SST GeoTIFFs in format PNG Portable Network Graphics Size: 3750.0 |
|---|---|
| Network links: |
<http://accession.nodc.noaa.gov/0077816> |
| Data format: | The file Pathfinder_v5.0_monthly&yearly_mean_daynight_SST.kml links to and displays monthly and yearly SST .png browse images included in this data set. Additional .kml files for individual years are in each yearly browse folder. in format KML Size: .21191 |
|---|---|
| Network links: |
<http://www.nodc.noaa.gov/archive/arc0041/0077816/2.3/data/0-data/Pathfinder_v5.0_SST-all_kml_file/Pathfinder_v5.0_monthly&yearly_mean_daynight_SST.kml> |
None for direct download. Contact the NODC for recovery fees for copy to hard media.
These data may be directly downloaded from the NOAA NODC Oceanographic Data Archive, or contact the NODC for custom orders (when ordering data from the NODC, a data set may be referred to by the 7-digit Accession Number listed in the RESOURCE DESCRIPTION field of this metadata record).
Within 24 hours for direct download
| Data format: | Global monthly and yearly SST averages developed from Pathfinder v. 5 day-night cloudscreened full resolution data in format TIFF GeoTIFF Size: 11250.0 |
|---|---|
| Network links: |
<ftp://ftp.nodc.noaa.gov/nodc/archive/arc0041/0077816/> |
| Data format: | Browse graphics associated with corresponding SST GeoTIFFs in format PNG GeoTIFFs exported to .png via ArcMap v10 Size: 3750.0 |
|---|---|
| Network links: |
<ftp://ftp.nodc.noaa.gov/nodc/archive/arc0041/0077816/> |
| Data format: | The file Pathfinder_v5.0_monthly&yearly_mean_daynight_SST.kml contains and displays monthly and yearly SST .png browse images included in this data set. Additional .kml files for individual years are in each yearly browse folder. in format KML Size: .21191 |
|---|---|
| Network links: |
<ftp://ftp.nodc.noaa.gov/nodc/archive/arc0041/0077816/> |
Navigate to the ftp location listed in this metadata record, or contact the NODC for custom orders (when ordering data from the NODC, a data set may be referred to by the 7-digit Accession Number listed in the RESOURCE DESCRIPTION field of this metadata record).
Usually within 24 hours.
Contact the NODC User Services Group via phone/FAX/E-mail: nodc.services@noaa.gov
PC, Mac, UNIX or other, standard Internet browser, ability to work with/utilize GIS files strongly recommended, knowledge of satellite data products
301-713-3280 x127 (voice)
301-713-3302 (FAX)
sheri.phillips@noaa.gov
