topCor {RStoolbox}

Topographic Illumination Correction

Description

account and correct for changes in illumination due to terrain elevation.

Usage

topCor(
  img,
  dem,
  metaData,
  solarAngles = c(),
  method = "C",
  stratImg = NULL,
  nStrat = 5,
  illu,
  ...
)

Arguments

img

SpatRaster. Imagery to correct

dem

SpatRaster. Either a digital elevation model as a RasterLayer or a RasterStack/Brick with pre-calculated slope and aspect (see terrain) in which case the layers must be named 'slope' and 'aspect'. Must have the same dimensions as img.

metaData

Character, ImageMetaData. Either a path to a Landsat meta-data file (MTL) or an ImageMetaData object (see readMeta)

solarAngles

Numeric vector containing sun azimuth and sun zenith (in radians and in that order). Not needed if metaData is provided

method

Character. One of c("cos", "avgcos", "minnaert", "C", "stat", "illu"). Choosing 'illu' will return only the local illumination map.

stratImg

RasterLayer or SpatRaster to define strata, e.g. NDVI. Or the string 'slope' in which case stratification will be on nStrat slope classes. Only relevant if method = 'minnaert'.

nStrat

Integer. Number of bins or quantiles to stratify by. If a bin has less than 50 samples it will be merged with the next bin. Only relevant if method = 'minnaert'.

illu

SpatRaster. Optional pre-calculated ilumination map. Run topCor with method="illu" to calculate an ilumination map

...

arguments passed to writeRaster

Details

For detailed discussion of the various approaches please see Riano et al. (2003).

The minnaert correction can be stratified for different landcover characteristics. If stratImg = 'slope' the analysis is stratified by the slope, i.e. the slope values are divided into nStrat classes and the correction coefficient k is calculated and applied separately for each slope class. An alternative could be to stratify by a vegetation index in which case an additional raster layer has to be provided via the stratImg argument.

Value

SpatRaster

References

Riano et al. (2003) Assessment of different topographic correction in Landsat-TM data for mapping vegetation types. IEEE Transactions on Geoscience and Remote Sensing.

Examples

## Load example data
metaData <- system.file("external/landsat/LT52240631988227CUB02_MTL.txt", package="RStoolbox")
metaData <- readMeta(metaData)

## Minnaert correction, solar angles from metaData
lsat_minnaert <- topCor(lsat, dem = srtm, metaData = metaData, method = "minnaert")

## C correction, solar angles provided manually
lsat_C <- topCor(lsat, dem = srtm, solarAngles = c(1.081533, 0.7023922), method = "C")