Resampling in Google Earth Engine: exporting Sentinel 1A to Google Drive

Question

I tried to export Sentinel 1A to Google Drive on Google Earth Engine. The function has a parameter name "scale" which determines pixel scale of the exported image.

Export.image.toDrive({
    image:imgtype[type],
    description: id,
    folder: folder,
    fileNamePrefix: id,
    region: region,
    scale: scale,
    maxPixels: maxPixels})
}

From the docs, it is said that Sentinel 1A has three resolution: 10m, 25m and 40m. My questions are:

1. If I set scale = one of three above scale, is the exported image original image or resampled image. And if it is resampled, then what resampling method is used?
2. If scale = another number (i.e. 20, 50, ...) then how GEE produce those images to Google Drive?

Answer 1

1. If you want to export the original image, set the crs, crsTransform and dimensions parameters to match the values of the original image. Setting the scale value may get you similar results, but scale is a less direct specification of the coordinate reference system (CRS).

2. If a different CRS is specified (using the scale or crs and crsTransform parameters), Earth Engine selects the nearest scaled image from the asset's image pyramid, and resamples (using nearest neighbor by default) as necessary. See the Scale documentation page for more details.

For even more details, see the Projections, Resampling and Reducing Resolution and Exporting Data pages of the Earth Engine documentation.