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avhrrlambert

Read AVHRR data product stored in eqaazim projection

Syntax

[latgrat,longrat,Z] = avhrrlambert(region,filename)
[...] = avhrrlambert(region,filename, scalefactor)
[...] = avhrrlambert(region,filename, scalefactor, latlim, lonlim)
[...] = avhrrlambert(region,filename, scalefactor, latlim, lonlim, gsize)
[...] = avhrrlambert(region,filename, scalefactor, latlim, lonlim, gsize,precision)

Description

[latgrat,longrat,Z] = avhrrlambert(region,filename) reads data from an Advanced Very High Resolution Radiometer (AVHRR) data set with a nominal resolution of 1 km that is stored in the Lambert Equal Area Azimuthal projection. Data of this type includes the Global Land Cover Characteristics (GLCC). region specifies the coverage of the file. Valid regions are listed in the following table. filename is a string specifying the name of the data file. Z is a geolocated data grid with coordinates latgrat and longrat in units of degrees. A scale factor of 100 is applied to the original data set such that Z contains every 100th point in both X and Y.

Region Specifiers
'a' or 'asia'
'af' or 'africa'
'ap' or 'australia/pacific'
'e' or 'europe'
'na' or 'north america'
'sa' or 'south america'

[...] = avhrrlambert(region,filename, scalefactor) uses the integer scalefactor to downsample the data. A scale factor of 1 returns every point. A scale factor of 10 returns every 10th point. The default value is 100.

[...] = avhrrlambert(region,filename, scalefactor, latlim, lonlim) returns data for the specified region. The result may extend somewhat beyond the requested area. The limits are two-element vectors in units of degrees, with latlim in the range [-90 90] and lonlim in the range [-180 180]. If latlim and lonlim are empty, the entire area covered by the data file is returned. If the quadrangle defined by latlim and lonlim (when projected to form a polygon in the appropriate Lambert Equal Area Azimuthal projection) fails to intersect the bounding box of the data in the projected coordinates, then latgrat, longrat, and Z are empty.

[...] = avhrrlambert(region,filename, scalefactor, latlim, lonlim, gsize) controls the size of the graticule matrices. gsize is a two-element vector containing the number of rows and columns desired. If omitted or empty, a graticule the size of the grid is returned.

[...] = avhrrlambert(region,filename, scalefactor, latlim, lonlim, gsize,precision) reads a data set with the integer precision specified. If omitted, 'uint8' is assumed. 'uint16' is appropriate for some files. Check the metadata (.txt or README) file in the ftp folder for specification of the file format and contents.

Background

The United States plans to build a family of satellite-based sensors to measure climate change under the Earth Observing System (EOS) program. Early precursors to the EOS data are the data sets produced by NOAA and NASA under the Pathfinder program. These are data derived from the Advanced High Resolution Radiometer sensor flown on the NOAA Polar Orbiter satellites, NOAA-7, -9, and -11 with a spatial resolution of about 1 km. The data from the AVHRR sensor is processed into separate land, sea, and atmospheric indices. Land area data is processed to a nondimensional vegetation index or land cover classification and stored in binary files in the Plate Carrée, Goode, and Lambert Equal Area Azimuthal projections. Sea data is processed to surface temperatures and stored in HDF formats. This function reads land cover data for the continents saved in the Lambert Equal Area Azimuthal projection at 1 km.

Examples

Example 1

Read and display every 100th point from the Global Land Cover Characteristics (GLCC) file covering North America with the USGS classification scheme, named nausgs1_2l.img.

[latgrat, longrat, Z] = avhrrlambert('na','nausgs1_2l.img');

Display the data using the Lambert Equal Area Azimuthal projection.

origin = [50 -100 0];
ellipsoid = [6370997 0];
figure
axesm('MapProjection', 'eqaazim', 'Origin', ...
   origin, 'Geoid', ellipsoid)
geoshow(latgrat, longrat, Z, 'DisplayType', 'texturemap');  

Example 2

Read and display every other point from the Global Land Cover Characteristics (GLCC) file covering Europe with the USGS classification scheme, named eausgs1_2le.img.

figure
worldmap france
mstruct = gcm;
latlim = mstruct.maplatlimit;
lonlim = mstruct.maplonlimit;
scalefactor = 2;
[latgrat, longrat, Z] = avhrrlambert('e', 'eausgs1_2le.img', ...
   scalefactor, latlim, lonlim);
geoshow(latgrat, longrat, Z, 'DisplayType', 'texturemap'); 
geoshow('landareas.shp','FaceColor','none','EdgeColor','black')

More About

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Tips

This function reads the binary files as is. You should not use byte-swapping software on these files.

The AVHRR project and data sets are described in and provided by various U.S. Government Web sites.

    Note   For details on locating map data for download over the Internet, see the following documentation at the MathWorks Web site: Finding Geospatial Data.

See Also

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