| ndvimap {greenbrown} | R Documentation |
This dataset is a multi-temporal map of Normalized Difference Vegetation Index (NDVI) from central Alaska. NDVI is a measure of vegetation greenness and is related to the coverage of green vegetation, photosynthetic activity and green biomass. NDVI ranges between -1 and 1. Bare ground and snow has usually NDVI values below 0.2, while vegetated areas have NDVI values above 0.2. Therefore, grid cells with long-term mean NDVI values below 0.2 were masked with NA. This mutli-temporal NDVI map is from the GIMMS (Global Inventory, Monitoring, and Modeling Studies) NDVI3g dataset that provides NDVI estimates from AVHRR (Advanced Very High Resolution Radiometer) satellite observations for 1982-2011. The original dataset has a bi-weekly temporal resolution. Some observations might be affected from snow or cloud cover. Therefore, the bi-weekly NDVI values were aggregated to monthly values using the maximum value. Each layer of this raster brick is a monthly time step between January 1982 and December 2011. The GIMMS NDVI3g dataset can be obtained from https://nex.nasa.gov/nex/projects/1349/.
A object of class brick.
Tucker, C.; Pinzon, J.; Brown, M.; Slayback, D.; Pak, E.; Mahoney, R.; Vermote, E.; El Saleous, N., An extended AVHRR 8-km NDVI dataset compatible with MODIS and SPOT VEGETATION NDVI data. International Journal of Remote Sensing 2005, 26, 4485-4498.
# load the NDVI map data(ndvimap) # print summary ndvimap # plot map plot(ndvimap) plot(ndvimap, 42) # plot selected time step # extract time series of a specific grid cell xy <- cbind(-152, 67) # coordinates of the grid cell ndvi.xy <- extract(ndvimap, xy) # extract NDVI time series for this pixel ndvi.xy <- as.vector(ndvi.xy) date <- as.Date(ndvimap@z$Date) # get vector of dates plot(date, ndvi.xy, type="l") # plot NDVI time series of the selected pixel