ABC3_README

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Canada-wide 1-km AVHRR Composite Maps Based on GEOCOMP Data Enhanced with ABC3v2
Software (October 2000)
Overview:
The ABC3v2 Canada-wide 1-km resolution AVHRR composite maps were produced as part of the CCRS
Northern BIosphere Observation and Modelling Experiment (NBIOME). NBIOME co-ordinated the
participation of a Canadian research team in the international Earth Observing System (EOS) to develop
methods for post-processing of AVHRR seasonal composite maps to produce derived products with
national coverage.
The ABC3v2 output products are used for various land cover, environmental monitoring and climate
change studies. Specialized products such as detailed land cover and biophysical parameter maps of
Fraction of Photosynthetically Active Radiation (FPAR) and Leaf Area Index (LAI) are required for
vegetated land cover studies. Albedo maps based on ABC3 data are used as input to the solar radiation
budget as part of global climate change studies.
Download advisory:
Since the data sets are packaged using UNIX tools, they are best served for UNIX platforms. Users
working on a PC with MS Windows NT or 2000 operating system need to set the WinZip properties to
correctly recover the image files. Under the Options menu, the user must select Configuration and then the
Miscellaneous tab. The box for “TAR file smart CR/LF conversion” should not be checked. Failure to
make this change can result in some of the data channels in the PCI Geomatics disk file containing
garbage. Also, by invoking the WinZip application before opening the compressed file, the user can modify
the folders used in the file recovery in order to avoid a disk space error.
GeoGratis Composite Product Summary:
Ten image product layers (described as end products) were selected as a subset from the ABC3v2 data set
(consisting of 39 product layers). They were made available to GeoGratis for each 10-day composite period
in a PCI Geomatics disk (.pix) file that contains 10 channels of 5700 pixels by 2400 lines as described in
the table below. All channels (product layers) are in 16-bit unsigned format except for the first channel
(RCECANT), which is in 8-bit unsigned format. The image data (originally generated in Lambert Conic
Conformal projection) were reprojected into the geographic (latitude/longitude) coordinate system using
the NAD83 datum and GRS 1980 ellipsoid. Given a pixel size of 1 minute in longitude and latitude, the
geographic coverage area is 50 degrees West to 145 degrees West in longitude and 40 degrees North to 80
degrees North in latitude.
Channel #
Channel 1:
Channel 2:
Channel 3:
Channel 4:
Channel 5:
Channel 6:
Channel 7:
Channel 8:
Channel 9:
Channel 10:
ABC3v2 Variable Name
RCECANT
B01_RRESUR_BRDF_INT
B02_RRESUR_BRDF_INT
B03_RRESUR_BRDF_INT
NDVI_RRESUR_BRDF_SMOOTH
REL_AZIMUTH
REL_DATE
SATELLITE_ZENITH
SUN_ZENITH
SURF_RTEMP_INT
Data Type
Contaminated Pixel Mask
Interpolated Surface Reflectance in Channel 1
Interpolated Surface Reflectance in Channel 2
Interpolated Surface Reflectance in Channel 3
Smoothed Surface NDVI
Relative Azimuth
Relative Date
Satellite Zenith Angle
Sun Zenith Angle
Interpolated Surface Temperature
GeoGratis Composite Product Detailed Description:
RCECANT: The contaminated pixel mask (that includes snow and ice) is a byte image indicating the
location of contaminated (0), water (127) and clear (255) pixels.
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B01_RRESUR_BRDF_INT: The interpolated surface reflectance in channel 1 is based on TOA reflectance
corrected for atmosphere using the SMAC code and corrected for BRDF effects using land cover specific
BRDF models. Contaminated pixels are replaced by temporal interpolation of seasonal data. Channel 1 and
2 values are adjusted equally to match the interpolated NDVI value. Channel 1 surface reflectance factors
have values from 0 to 1 and are scaled to a range between 0 and 1000.
B02_RRESUR_BRDF_INT: The interpolated surface reflectance in channel 2 is based on TOA reflectance
corrected for atmosphere using the SMAC code and corrected for BRDF effects using land cover specific
BRDF models. Contaminated pixels are replaced by temporal interpolation of seasonal data. Channel 1 and
2 values are adjusted equally to match the interpolated NDVI value. Channel 2 surface reflectance factors
have values from 0 to 1 and are scaled to a range between 0 and 1000.
B03_RRESUR_BRDF_INT: The interpolated surface reflectance in channel 3 is based on surface
reflectance corrected for BRDF effects using a land cover specific BRDF correction. The replacement of
contaminated pixels is based on temporal interpolation of seasonal composite data. Channel 3 surface
reflectance factors have values from 0 to 1 and are scaled to a range between 50 and 1050.
NDVI_RRESUR_BRDF_SMOOTH: The smoothed NDVI is computed from the BRDF-corrected surface
reflectance for channels 1 and 2. Contaminated pixels are replaced by temporal interpolation of seasonal
data. Finally, a 5-point smoothing filter is applied to the seasonal NDVI curve. NDVI values from –1 to 1
are scaled to a range between 0 and 20,000. Obviously, the interpolated products are no longer of value for
snow/ice studies as these pixels have been identified as contaminated pixels and have been replaced!
REL_DATE: The relative date is the number of days since 01-Jan-1970 of the corresponding imagery
pixel. A relative date of 8501 translates to 11-APR-1993.
REL_AZIMUTH: The relative azimuth angle is measured clockwise (0-360) between the sun azimuth
angle and the satellite azimuth angle for the corresponding imagery pixel. Angle data in degrees are scaled
to a range between 0 and 18,000.
SATELLITE_ZENITH: The satellite or view zenith angle is measured between the vector normal to the
earth's surface at the pixel and the vector from the pixel to the satellite. Angle data in degrees are scaled to
a range between 0 and 18,000.
SUN_ZENITH: The sun zenith angle is measured between the vector normal to the earth's surface at the
pixel and the vector from the pixel to the sun. Angle data in degrees are scaled to a range between 0 and
18,000.
SURF_RTEMP_INT: The smoothed surface temperature is derived from the brightness temperature from
channels 4 and 5 corrected for atmospheric and surface emissivity effects. Contaminated pixels are replaced
by temporal interpolation of seasonal data but not for the end points. An upper cut-off value of 330 degrees
Kelvin was used for Canada. Surface temperature values from 0 to 350 degrees Kelvin are scaled to a range
of 0 to 3500.
GeoGratis Browse Product Summary:
To facilitate the potential benefit of the composite product a browse image (.jpg) in JPEG format
(compression quality of 75 as specified in PCI FEXPORT task) is included in the data download for user
perusal. This browse image was created by subsampling the full resolution composite product by a factor of
ten using nearest neighbour resampling. The browse image also in geographic (latitude/longitude)
projection contains 570 pixels by 240 lines at 10-km resolution. The three product layers
NDVI_RRESUR_BRDF_SMOOTH, B02_RRESUR_BRDF_INT and B01_RRESUR_BRDF_INT were
encoded as red, green and blue, respectively, in a false colour composite. As JPEG format only supports 8bit data, the product layers were rescaled as follows:
1) for NDVI_RRESUR_BRDF_SMOOTH, scaled values of 9000-20000 were remapped to 0-255;
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2) for B02_RRESUR_BRDF_INT, scaled values of 0-650 were remapped to 0-255; and
3) for B01_RRESUR_BRDF_INT, scaled values of 0-350 were remapped to 0-255.
ABC3v2 Data Processing and Algorithm Details:
Full details on the ABC3v2 data processing and other image product layers available from the complete
ABC3v2data set are provided in the MS Word document ABC3v2.doc that is included in the download
bundle. The ABC3v2 software as compiled in C on a desktop computer with a Microsoft Windows 2000
operating system is available from CCRS upon request. For further information on the data set including
the availability of image data in LCC projection and access to the source code, please contact Josef Cihlar
(e-mail [email protected]).
Acknowledgements:
All data are the Copyright of the Canada Centre for Remote Sensing, Natural Resources Canada. CCRS
requests reprints of any published papers or reports or a brief description of other uses (e.g., posters, oral
presentations, etc.) of ABC3v2 data. This will help CCRS determine the use of distributed data and will
assist in the optimization of product development and validation. Please include the following reference in
any journal articles resulting from the use of ABC3v2 data:
Cihlar, J., Latifovic, R., Chen, J., Trishchenko, A., Du, Y., Fedosejevs, G., and Guindon, B. 2001.
“Systematic corrections of AVHRR image composites for temporal studies”, Remote Sensing of
Environment (accepted).
MS Word document ABC3_README.doc last updated by Gunar Fedosejevs on December 5, 2001.
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