minnaert {landsat}

Whole-image and pixel-based Minnaert topographic correction of remote sensing data.

Description

Adds several modified Minnaert corrections to the capabilities of topocorr().

Usage

minnaert(x, slope, aspect, sunelev, sunazimuth, na.value = NA, GRASS.aspect=FALSE, 
	IL.epsilon=0.000001, slopeclass = c(1, 5, 10, 15, 20, 25, 30, 45), coverclass)

Arguments

x

Image to be corrected, in matrix, data frame, or SpatialGridDataFrame format.

slope

Slope image of same size and resolution as x.

aspect

Aspect image of same size and resolution as x.

sunelev

Sun elevation in degrees.

sunazimuth

Sun azimuth in degrees.

na.value

Value to use for missing data.

GRASS.aspect

Whether aspect is measured according to GRASS defaults (counterclockwise from east) or is measured clockwise from north. If GRASS.aspect=TRUE, aspect is converted to clockwise from north before analysis.

IL.epsilon

If IL == 0 (Illumination), some methods will give a topographically-corrected value of Inf due to division by zero. If desired, adding a small increment to zero values eliminates this.

slopeclass

The classes into which the slope will be divided before calculating k separately for each class.

coverclass

If present, TRUE/FALSE vector indicating which pixels to use when calculating k. This allows k to be determined separately for different cover classes.

Details

Calculates the Minnaert k coefficients for the whole image and for the individual slope classes.

Value

allcoef

The Minnaert k for the entire image. This is the value used in topocorr() (though the latter may have been truncated).

classcoef

A data frame containing the slope class midpoints, number of pixels per class, and k for that class (for the desired cover class, if specified).

xout

A topographically-corrected image in the same format as x.

xout

A topographically-corrected image in the same format as x.

Author(s)

Sarah Goslee

References

Lu, D., Ge, H., He, S., Xu, A., Zhou, G., and Du, H. 2008. Pixel-based Minnaert correction method for reducing topographic effects on a Landsat 7 ETM+ image. Photogrammetric Engineering and Remote Sensing 74:1343-1350.

See Also

topocorr

Examples

	# require slope and aspect for topographic correction
	data(dem)
	dem.slopeasp <- slopeasp(dem)

	# use cosine method of topographic correction
	data(july4)
	july4.minpix <- minnaert(july4, dem.slopeasp$slope, dem.slopeasp$aspect, 
		sunelev=61.4, sunazimuth=125.8, slopeclass=c(1, 5, 10, 15, 50))
	july4.minpix$classcoef # all coefficients