spectral indices - including kNDVI

R/indices.R

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+#' Remote sensing spectral indices
+#'
+#' This function allows to obtain several remote sensing spectral indices in the optical
+#' domain.
+#'
+#' @references
+#' Rouse, J.W., Hass, R.H., Schell, J.A., and Deering, D.W. (1973). Monitoring vegetation systems in the
+#' Great Plains with ERTS. Proceedings of the Third ERTS Symposium, 1.
+#'
+#' Huete, A.R. (1988). A Soil-Adjusted Vegetation Index (SAVI). Remote Sensing of
+#' Environment, 25,295-309.
+#'
+#' Huete, A.R., Justice, C., Liu, H. (1994). Development of vegetation and soil indices for MODIS-EOS.
+#' Remote Sensing of Environment, 49, 224-234.
+#'
+#' Gao, B.C. (1996). NDWI—A normalized difference water index for remote sensing of vegetation
+#' liquid water from space. Remote Sensing of Environment, 58, 257-266.
+#'
+#' Key, C.H.; Benson, N.C. Landscape Assessment: Ground Measure of Severity, the Composite
+#' Burn Index, and Remote Sensing of Severity, the Normalized Burn Index. In FIREMON:
+#' Fire Effects Monitoring and Inventory System; Lutes, D., Keane, R., Caratti, J., Key,
+#' C.H., Benson, N.C., Sutherland, S., Gangi, L., Eds.; Rocky Mountains Research Station,
+#' USDA Forest Service: Fort Collins, CO, USA, 2005.
+#'
+#' Camps-Valls, G., et al. (2021). A unified vegetation index for quantifying the terrestrial
+#' biosphere. Science Advances, 7(9).
+#'
+#' @note
+#' Currently implemented for satellites such as Landsat-4 TM, Landsat-5 TM, Landsat-7 ETM+,
+#' Landsat-8 OLI and Sentinel-2, and any other sensor who has the appropriate bands. It is
+#' possible to obtain spectral indices through digital number or top of atmosphere reflectance
+#' (toa), however in order to calculate indices such as SAVI or EVI, the the data must be in
+#' surface reflectance.
+#'
+#' @param index Character, index name.
+#' @param blue Blue band, raster object.
+#' @param green Green band, raster object.
+#' @param red Red band, raster object.
+#' @param nir Near-infrared band, raster object.
+#' @param redEdge Red-edge band, raster object.
+#' @param swir Short-wave-infrared band, raster object.
+#' @param coefs List of coefficients to be used in some indices (Lsavi = 0.5, G = 2.5,
+#' C1 = 6, C2 = 7.5, Levi = 1).
+#'
+#' @examples
+#' library(ForesToolboxRS)
+#' library(raster)
+#'
+#' # Load an example dataset
+#' data(img_l8)
+#'
+#' # Obtain bands
+#' nirBand <- img_l8[[4]]
+#' redBand <- img_l8[[3]]
+#'
+#' # Obtain NDVI
+#' ndvi <- indices(index = "NDVI", nir = nirBand, red = redBand)
+#' plot(ndvi)
+#'
+#' @export
+#'
+indices <- function(index, blue = NULL, green = NULL, red = NULL, nir = NULL, redEdge = NULL,
+                    swir = NULL, coefs = list(Lsavi = 0.5,  G = 2.5, C1 = 6, C2 = 7.5, Levi = 1)) {
+
+  layersR <- c(class(blue), class(green), class(red), class(nir), class(redEdge), class(swir))
+
+  if (any(layersR == "RasterBrick" | layersR == "RasterStack")) stop("image must be a Raster object (RasterLayer). One band", call. = TRUE)
+
+  if (index == "NDVI") {
+
+    indx <- (nir - red)/(nir + red)
+    names(indx) <- "NDVI"
+
+  } else if (index == "SAVI") {
+
+    indx <- (1 + coefs[['Lsavi']])*(nir - red)/(nir + red + coefs[['Lsavi']])
+    names(indx) <- "SAVI"
+
+  } else if (index == "EVI") {
+
+    if (missing(blue)) stop("nir, red and blue bands are needed.", call. = TRUE)
+
+    indx <- coefs[['G']]*(nir - red)/(nir + coefs[['C1']]*red - coefs[['C2']]*blue + coefs[['Levi']])
+    names(indx) <- "EVI"
+
+  } else if (index == "NDWI") {
+
+    indx <- (green - nir)/(green + nir)
+    names(indx) <- "NDWI"
+
+  } else if (index == "NBR") {
+
+    indx <- (nir - swir)/(nir + swir)
+    names(indx) <- "NBR"
+
+  } else if (index == "NDSI") {
+
+    indx <- (green - swir)/(green + swir)
+    names(indx) <- "NDSI"
+
+  } else if (index == "kNDVI") {
+
+    sigma <- 0.5*(nir + red)
+    var <- (nir - red)/(2*sigma)
+    # Values
+    vr <- getValues(var)
+    # NA
+    iNA <- which(!is.na(vr)) # NA positions
+    # Get kNDVI
+    indx <- raster(nir)
+    indx[iNA] <- tanh(na.omit(vr))
+    names(indx) <- "kNDVI"
+
+  } else {
+    stop("Index not supported.")
+  }
+
+  return(indx)
+}
+