15
votes
Accepted
Creating Sentinel-2 NDVI time series chart in Google Earth Engine?
You are using the variable NDVI to compute the chart, but this variable is a single image, because you applied median(). If you want a time series plot you have to compute the chart using the NDVI ...
- 1,541
14
votes
Writing code for monthly NDVI medians in Google Earth Engine?
For the record, here is a good way to do this:
var imageCollection = ee.ImageCollection("LANDSAT/LT05/C01/T1");
var months = ee.List.sequence(1, 12);
var composites = ee.ImageCollection.fromImages(...
- 4,309
9
votes
EVI and NDVI range value
You are right: the range of the NDVI is limited to values between -1 and 1 due to its' normalization properties.
The negative limit of -1 will be reached if you encounter maximal reflectance (1) in ...
- 176
9
votes
Accepted
Which NIR bandwidth is suitable to Calculate NDVI?
Between 770 and 1040 nm, you are nearly on a plateau in term of reflectance from the green vegetation (in fact, it decreases a little bit when the wavelength increases), so your green vegetation NDVI ...
- 49.3k
8
votes
Rescaling NDVI values 0-255 to [-1;1] using ArcGIS Raster Calculator?
Using the raster calculator, you'll want to rescale your NDVI image. The formula you'll want to use is:
NDVI = 2/255*image-1
This is simply the linear regression between 0 to 255 and -1 to 1, ...
- 6,486
8
votes
Tutorial Vegetation Condition Index
Kogan (2004) (p. 2891) provides the following formula for the Vegetation Condition Index (VCI):
VCI = 100 * (NDVI - NDVImin) / (NDVImax - NDVImin)
where,
NDVI = Smoothed weekly NDVI value
NDVImin ...
- 51.4k
8
votes
Accepted
Using a fixed palette range to plot an NDVI raster in R
You need to supply levelplot() with a bit more information, via its at= argument, so that it can know the set of intervals to which you want the colors in col.regions applied.
library(rasterVis)
## ...
- 925
8
votes
Accepted
Making stack from many images in Google Earth Engine?
You just need the function 'toBands()' and apply that on the image collection. Unfortunately, the function cannot deal with similar band names (at least, for your MODIS collection: it works fine for ...
- 9,913
7
votes
Using Loop for calculating NDVI in R?
There's no need for a for (or any other kind of) loop since such stuff is entirely included in the raster package. If you want to calculate the NDVI, then basically all you need is
## required ...
- 5,183
7
votes
Accepted
Extracting LANDSAT time-series data by polygon using Google Earth Engine?
The code that you copied uses an Earth Engine object of type "Image", and Image objects have a method/function named clip. Your reworked code (i.e. Landsat) uses an Earth Engine object of type "...
- 5,371
7
votes
Accepted
Why is a normalized parameter involving the Green band and Red band not used for Vegetation determination?
The best explanation I came across is this:
the ratio of the difference of the red and infrared radiances over their sum as a means to adjust for or “normalize” the effects of the solar zenith ...
- 12k
7
votes
Accepted
Why vegetation index, NDVI or SAVI is not working in the desert?
The sensitivity of the normalized difference vegetation index (NDVI) to the soil background and atmospheric effects has generated an increasing interest in the development of new indices. The NDVI ...
- 1,725
7
votes
Accepted
Smoothing/interpolating across images in an ImageCollection to remove missing data
You can replace the values using where().
// Replace masked pixels by the mean of the previous and next months
// (otherwise, how to deal with the first images??)
var replacedVals = composites.map(...
- 9,913
7
votes
Problem generating NDVI chart in GEE
You are using an image property that does not exist. Use system:index instead of system:time_start.
// Chart a single year mean of SB
var TS1 = ui.Chart.image.series(modisNDVI, geometry, ee.Reducer....
- 1,541
7
votes
Accepted
Rescale NDVI (-1:1) to 0-255 using R
SOLVED using rescaleImage() function in RStoolbox:
library(RStoolbox)
ndvi <- rescaleImage(x= ndvi, xmin = -1, xmax = 1, ymin=0, ymax=255)
Now I get the expected results:
ndvi
class : ...
- 1,084
6
votes
Accepted
Classify forest with NDVI from Landsat 8 and 7
No, the NDVI threshold value will not be the same for the time series due to differences in phenology and unique conditions on the ground. As Kersten mentioned in the comments, you may want to ...
- 51.4k
6
votes
Accepted
Difference between Landsat 7 and Landsat 8 TOA reflectance computation
The two products are comparable with some initial considerations. As you can see, the resolutions of the products are more or less the same:
To give a more visual comparison of the spectral bands ...
- 4,558
6
votes
Accepted
landsat NDVI time series plot in R, based on point or pixel
Do you want an interactive map, or are you fine with plotting the NDVI timeseries for one (or few) specific points? In the latter you raster::extract() the NDVI-Stack values under your points, and use ...
- 366
6
votes
Accepted
Calculating Landsat 7 NDVI images using QGIS
Testing and comparing a Landsat 7 image (different area to yours, but same sensor data) reveals that the values are in fact both "correct".
You (and I) have fallen into the trap of the Raster ...
- 713
6
votes
Accepted
Viewing bands of landsat 8 images in QGIS for NDVI calculation?
You have downloaded the data and you can find it if you unpack the .tar.gz file using 7zip or similar software for unpacking files. The .tar.gz file is the fourth file from the top that can be seen in ...
- 6,486
6
votes
Arcpy reclassify with function
This is how I would do it (it requires the Spatial Analyst extension which I think you have):
import arcpy
from arcpy.sa import *
arcpy.CheckOutExtension = "Spatial"
ndvi_raster = Raster("...
- 3,737
6
votes
Accepted
Calculating NDVI
Start the filename of the output raster with a character not a number, i.e NDVI_1988_1 instead of 1988_NDVI_1
From the Esri FAQ: What characters should not be used in ArcGIS for field names and table ...
- 64k
5
votes
How to smooth NDVI raster (Sentinel 2-A image) in ArcGis?
For visualisation purpose, you can select a resampling method from the display properties. right click on layer > properties, then display tab / resampling during display using : cubic convolution (...
- 49.3k
5
votes
Obtaining something like NDVI value from Sentinel-1 product
Um, the Sentinel-1 sensor is C-band SAR (radar) data, not spectral. Given that NDVI is a spectral index of photosynthetically active radiation using the ratio between Red and NIR spectra, what makes ...
- 31.3k
5
votes
Pixel-wize trend analysis of an irregular time series stack of NDVI rasters in R
I guess I found a way to my own problem:
Basically, I parsed the time variable from the filename and added it back to regression model. Below is the peice of code I used.
library(raster)
all <...
- 287
5
votes
Mask clouds in LandSat 8 surface refletance image
The Surface Reflectance products contain a band called 'cfmask' and 'cfmask_conf'. The documentation tells you that all pixels labelled 4 in the first band are clouds. If you just want to mask clouds ...
- 9,775
5
votes
Accepted
Do clouds reflect NIR/Red bands
Yes, it affects the values of NDVI, and it may not give the desired results sometimes. Information from Wikipedia: Normalized Difference Vegetation Index provides some details about the effects of ...
- 40.3k
5
votes
Calculate NDVI using ArcPy Spatial Analyst
I presume you're using ArcGIS Desktop which uses python 2x, not ArcGIS Pro which uses python 3x. Side note: this is one example of why it's important to specify the software you are using.
In python ...
- 64k
5
votes
Difference between types of Vegetation indices
Not all indices are from -1 to 1.
For example, REP (red-edge position) index could start near to 600 and end near to 800 nm. In the other hand, for any Normalized Difference Index, you can expect to ...
- 13.1k
5
votes
Purchasing NDVI imagery for South Western England?
I don't think this is the answer you're looking for but with the specifications you describe, unless there is a subscription through which the farmers need to finance imagery purchase, it would ...
- 3,078
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