Note: This document is for an older version of GRASS GIS that has been discontinued. You should upgrade, and read the current manual page.
Prior to spectral unmixing the pixel values (DN) of the Landsat scene need to be converted to reflectance values (here: using DOS1):
# rename channels or make a copy to match i.landsat.toar's input name scheme: g.copy raster=lsat7_2002_10,lsat7_2002.1 g.copy raster=lsat7_2002_20,lsat7_2002.2 g.copy raster=lsat7_2002_30,lsat7_2002.3 g.copy raster=lsat7_2002_40,lsat7_2002.4 g.copy raster=lsat7_2002_50,lsat7_2002.5 g.copy raster=lsat7_2002_61,lsat7_2002.61 g.copy raster=lsat7_2002_62,lsat7_2002.62 g.copy raster=lsat7_2002_70,lsat7_2002.7 g.copy raster=lsat7_2002_80,lsat7_2002.8
# set computational region to first Landsat band g.region raster=lsat7_2002_10 -p i.landsat.toar input=lsat7_2002. output=lsat7_2002_toar. sensor=tm7 \ method=dos1 date=2002-05-24 sun_elevation=64.7730999 \ product_date=2004-02-12 gain=HHHLHLHHL
In order to obtain pure spectra ("endmembers") to be searched for during the spectral unmixing process later on we can either obtain them from spectral libraries (ASTER Spectral Library, USGS Spectral Library, field spectrometer, etc.) or through a PCA analysis as follows.
In order to identify pure endmembers, they are supposed to be in the corners of the PCA feature space:
i.pca -n input=lsat7_2002_toar.1,lsat7_2002_toar.2,lsat7_2002_toar.3,lsat7_2002_toar.4,lsat7_2002_toar.5,lsat7_2002_toar.7 \ output=pca_lsat7_2002_toar d.mon wx0 # d.correlate or use scatterplot tool in g.gui d.correlate map=pca_lsat7_2002_toar.1,pca_lsat7_2002_toar.2 # TODO: problem: how to obtain the unprojected coordinates for the corner pixels? # (in 1998 the xgobi software did this nicely, check today's ggobi)
Sample content of "spectrum.dat":
# Channels: r g b i1 i2 i3 # Enter spectra linewise! # 1. Sagebrush # 2. Saltbush # 3. Soil # 4. Dry grass # Matrix: 4 by 6 row0: 8.87 13.14 11.71 35.85 28.26 10.54 row1: 13.59 20.12 19.61 70.66 34.82 16.35 row2: 28.26 34.82 38.27 40.1 38.27 23.7 row3: 10.54 16.35 23.7 38.98 40.1 38.98
i.group group=lsat7_2002_toar subgroup=lsat7_2002_toar \ input=lsat7_2002_toar.1,lsat7_2002_toar.2,lsat7_2002_toar.3,lsat7_2002_toar.4,lsat7_2002_toar.5,lsat7_2002_toar.7 i.spec.unmix group=lsat7_2002_toar matrix=sample/spectrum.dat result=lsat7_2002_unmix \ error=lsat7_2002_unmix_err iter=lsat7_2002_unmix_iterations # todo: reclass to 0..100%
Mohammed Rashad (rashadkm gmail.com) (2012, update to GRASS 7)
Available at: i.spec.unmix source code (history)
Latest change: Monday Nov 11 18:04:48 2024 in commit: 59e289fdb093de6dd98d5827973e41128196887d
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