Calculate water area of SAR images of Google Earth Engine

Question

I use this link to extract surface area of water bodies from SAR images

Google Earth Engine ROI area falling outside/partial coverage by Sentinel 1 Tile

But now I would like to calculate the area of inundated areas and export them to CSV file but when running this code, the Error

flooded.multiply is not a function

What can I do ?

var flooded = S1.select("Water")
Map.addLayer(flooded,
 {min:0, max:1, palette: ['grey', 'blue']},
 'flooded')

var areaImage = flooded.multiply(ee.Image.pixelArea())

var area = areaImage.reduceRegion({
  reducer: ee.Reducer.sum(),
  geometry: aoi.geometry(),
  scale: 10,
  maxPixels: 1e10
  })

Answer 1

Flooded is still an imageCollection so you have to select 1 image out that collection:

var areaImage = flooded.first().multiply(ee.Image.pixelArea())
var area = areaImage.reduceRegion({
  reducer: ee.Reducer.sum(),
  geometry: aoi.geometry(),
  scale: 10,
  maxPixels: 1e10
  })

In this example I selected the first image with first(), but you can also select different images. I can highly recommend doing some tutorials which cover these basic differences between images and imageCollections: https://developers.google.com/earth-engine/tutorials/tutorials

Answer 2

var flooded = S1.select("Water")
var areaImage = flooded.multiply(ee.Image.pixelArea())

var area3 = areaImage.reduceRegion({
  reducer: ee.Reducer.sum(),
  geometry:  aoi.geometry(),,
  scale: 10,
  maxPixels: 1e10
  })

var flooded_area3 = ee.Number(area3.get('classification')).divide(10000).round();