Mapping Toolbox    
avhrrgoode

Read AVHRR data stored in the Goode Projection

Syntax

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 datasets 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, and have spatial resolutions 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 non-dimensional vegetation index or land cover classification and stored in binary files in the Plate Carree, Goode and Lambert projections. Sea data is processed to surface temperatures, and stored in HDF formats. This function reads land data saved in the Goode projection with global and continental coverage at 1 km. It can also read 8 km data with global coverage.

Description

[latgrat,longrat,map] = avhrrgoode reads data from an AVHRR dataset with a nominal resolution of 1 km. These files have 17347 rows and 40031 columns of data, or somewhat more than the capacity of one CD-ROM. The file is selected interactively. Data is returned as a general matrix map with the graticule matrices in units of degrees.

avhrrgoode(region) Reads data from a file with data covering the specified region. Valid regions are 'g' or 'global', 'af' or 'africa', 'ap' or 'australia/pacific', 'ea' or 'eurasia', 'na' or 'north america', and 'sa' or 'south america'. The file is selected interactively. If omitted, 'global' is assumed.

avhrrgoode(region,filename) uses the provided filename.

avhrrgoode(region,filename,scalefactor) uses the integer scalefactor to down-sample the data. A scale factor of 1 returns every point. A scale factor of 10 returns every 10th point. If omitted, 100 is assumed.

avhrrgoode(region,filename,scalefactor,latlim,lonlim) returns data for the specified region. The returned data will extend somewhat beyond the requested area. If omitted, the entire area covered by the data file is returned. The limits are two-element vectors in units of degrees, with latlim in the range [-90 90] and lonlim in the range [-180 180].

avhrrgoode(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 map is returned.

avhrrgoode(region,filename,scalefactor,latlim,lonlim,gsize,fnrows,fncols) overrides the standard file format for the selected region. This is useful for data stored on CD-ROM, which may have been truncated to fit. Some data was distributed with 16347 rows and 40031 columns of data on CD-ROMs. Non-dimensional vegetation index data at 8 km spatial resolution has 2168 rows and 5004 columns.

avhrrgoode(region,filename,scalefactor,latlim,lonlim,gsize,fnrows,fncols,resolution) reads a dataset with the spatial resolution specified in meters. If omitted, the full resolution of 1000 meters is assumed. Data is also available at 8000 meter resolution.

avhrrgoode(region,filename,scalefactor,latlim,lonlim,gsize,fnrows,fncols,resolution,precision) reads a dataset with the integer precision specified. If omitted, 'uint8' is assumed. 'uint16' is appropriate for some files. Check the data's README file for specification of the file format and contents.

Remarks

The AVHRR project and datasets are described in:

http://daac.gsfc.nasa.gov/DATASET_DOCS/avhrr_dataset.html

http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/FTP_SITE/readmes/pal.html

http://edcwww.cr.usgs.gov/landdaac/1KM/1kmhomepage.html

http://edcwww.cr.usgs.gov/landdaac/glcc/glcc_na.html

Some sources for the data include:

ftp://daac.gsfc.nasa.gov/data/avhrr/

ftp://edcftp.cr.usgs.gov/pub/data/glcc/

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

Examples

Read a 1 km Global Land Cover Classification (GLCC) file using the default parameters. Select the file 'gusgs1_2.img' interactively. This file is available from <ftp://edcftp.cr.usgs.gov/pub/data/glcc/globe/gusgs1_2.img.gz>.

Read the same file at full resolution for just the island of Cyprus.

Read the GLCC urban areas file covering North America in the Goode projection for just the area of eastern Massachusetts. This file is available from <ftp://edcftp.cr.usgs.gov/pub/data/glcc/na/goode/naurbang.img.gz>.

Read the global data on the "Global Land 1-km AVHRR Data Set - Vegetation Index 6/21-30, 1992" CD-ROM (distributed by the Land Processes Distributed Active Archive Center, EROS Data Center, Sioux Falls, South Dakota, 57198, USA). Sample every 100th point for the entire globe, returning one lat and long for value. Provide the non-standard number of rows and columns in the file.

Read the global 8 km resolution non-dimensional vegetation index available from <ftp://daac.gsfc.nasa.gov/data/avhrr/global_8km/.1994_1997/1994/jun/avhrrpf.ndvi.1ntfgl.940621.gz>. Sample every 10th point for the entire globe, returning one lat and long for value. Provide the non-standard number of rows, columns and resolution in the file.

Read the global 8 km resolution data for AVHRR sensor channel 4 available from <ftp://daac.gsfc.nasa.gov/data/avhrr/global_8km/.1981_1985/1984/feb/avhrrpf.ch4.1ntfgl.840201.gz>. Read at the full 8 km resolution for the island of Cyprus, returning one lat and long for value. Provide the non-standard number of rows, columns, resolution and integer precision in the file.

Limitations

Most files store the data in scaled integers. Though this function returns the data as double, the scaling from integer to float is not performed. Check the data's README file for the appropriate scaling parameters.

Subsets of the land cover data are available in both the Goode and the uninterrupted Lambert azimuthal projections. Data can be read more quickly from the Lambert projection using avhrrlambert.

This function does not have the proper projection parameters to read the regional 8 km resolution datasets.

See Also
avhrrlambert
 Read AVHRR data in the Lambert Azimuthal Equal-Area projection


  Alphabetical listing of External Interface Functions avhrrlambert