Adding a new band calculated to a ASTER Image Collection

Question

I'm trying to calculate a sintetic band, rename it and add to image collection in order to constitute a natural false color ASTER images.

    //Filtering

var image = imageCollection2.filterBounds(geometry)
                          .filterDate('2000','2021')
                          .filterMetadata('CLOUDCOVER', 'less_than',0.5)
                          ;




//Calculate a new band and renaming it

var image_sint = image.map(function (image){
  var  sint = image.expression(
    '((banda1 *3)+banda3)/4',
    {'banda1': image.select('B01'),
    'banda3' : image.select('B3N')
    }).rename('sint');
    return image.addBands('sint');
});


//Visual Parameters

var paramvis = {bands: ['B02','sint','B01' ]};


//Adding to view
Map.addLayer(image_sint, paramvis,'final');

Answer 1

This approach fix the problem:

//Filtering

var image = imageCollection2.filterBounds(geometry)
                          .filterDate('2000','2021')
                          .filterMetadata('CLOUDCOVER', 'less_than',0.5)
                          ;

//Calculate a new band and renaming it

var image_sint = image.map(function (image){
  return image.expression(
    '((banda1 *3)+banda3)/4',
    {'banda1': image.select('B01'),
    'banda3' : image.select('B3N')
    }).rename('sint').addBands(image);
});


//Visual Parameters

var paramvis = {bands: ['B02','sint','B01' ]};


//Adding to view

Map.addLayer(image_sint, paramvis,'final');

here a example: link

Answer 2

The problem is that you are trying to add a string as a new band instead of the name of the object of interest. Just remove the single quotations around sint in addBands.

return image.addBands(sint);