Google Earth Engine – How to Obtain NDVI Mean Value for Specific Point Across Multiple Sites

Question

I'm trying to get multiple site at the same time from LANDSAT 8. The next error appears when I run it.

ImageCollection (Error)
Error in map(ID=20210906):
Image.reduceRegions: The default WGS84 projection is invalid for aggregations. Specify a scale or crs & crs_transform.

The code below:

var fechafin= ('2022-02-28')
var fechaini = ('2021-09-01')

 Filter collection to dates of interest.
var NDVI = ee.ImageCollection('LANDSAT/LC08/C01/T1_8DAY_NDVI')
.filterDate(fechaini, fechafin)
.filterBounds(potreros)
.select('NDVI')
print(NDVI)

// Transform NDVI in Radi Landsaatt NDVIi

var addDate = function(image){
  var doy = image.date().getRelative('day', 'year')
var doyBand = ee.Image.constant(doy).uint16().rename('doy')
  return image.addBands(doyBand)
}
var NDVIn = NDVI.map(addDate)
print('n',NDVIn)

var addPAR = function(image){
var f = image.expression('15.402168 - 0.000000011*(x**4) + 0.000007543*(x**3) - 0.001310832*(x**2) + 0.009646584*x', {
      'x': image.select('doy')
  }).rename('PAR')
  return image.addBands(f)
}
var NDVIo = NDVIn.map(addPAR)
print('o',NDVIo)

var addfPAR = function(image){
//var f = image.expression('min(max((1+NDVI)/(1-NDVI)/9.916077458,0),0.95)', {
var f = image.expression('min(max(0.008* exp(5.41 * (NDVI/10000)),0),0.95)', {
      'NDVI': image.select('NDVI')
  }).rename('fPAR')
 
  return image.addBands(f)
}
var NDVIp = NDVIo.map(addfPAR)
print('p',NDVIp)

var addAPAR = function(image){
var f = image.expression('PAR*fPAR', {
      'fPAR': image.select('fPAR'),
      'PAR': image.select('PAR')
  }).rename('APAR')
 
  return image.addBands(f)
}
var NDVIq = NDVIp.map(addAPAR)
print('q',NDVIq)

////////////////////////////////////////////////////////////
// Export
////////////////////////////////////////////////////////////

var datos = NDVIq.map(function(i){
  return i.reduceRegions(potreros, 'first')
})
print('datos11',datos)
var extract = ee.FeatureCollection(datos.flatten())
print(extract)

Export.table.toDrive({
  collection: extract,
  description: 'NDVI_fPAR',
  fileFormat: 'CSV',
});

Answer 1

Based in your error message, I search which is the command syntax for reduceRegions in this link. So, I modified following function in your code as:

var datos = NDVIq.map(function(i){
  return i.reduceRegions(potreros, ee.Reducer.mean(), 30);
});

After running complete code in GEE code editor (I assumed an arbitrary area for potreros geometry), it ran without any issue; as it can be observed in following picture.