How to copy metadata from one image collection to another?

[radwinskis]

Hi there,

I have been trying to create an image collection of Landsat imagery, where I have written script to mosaic images from two tiles/scenes taken on the same day and to clip the imagery to a region. However, I have noticed that when I mosaic images, as well as clip images, I lose all metadata. It makes sense, as a new image collection is made and EE assumes the metadata would be different, but I would like to keep some metadata from one of the two Landsat tiles used for the daily mosaics.

In the EE documentation I have found the ImageCollection.copyProperties() function but keep receiving attribute errors when trying to call on the new image collection with the properties copied. I have tried implementing the copyProperties function by creating an image collection with just the tile/scene I would like to take metadata from, which is the same length of images as the mosaiced collection, and called on different metadata properties. Ultimately, I would imagine I am implementing the function incorrectly but examples of the function (in javascript) seem to be employed similarly to how I am trying to employ the function here. Can't seem to find any other functions or ways to accomplish this.

What is a good way to go about copying metadata from one image collection, or image, to another (assuming they are the same length of images)? I would imagine there must be a good way to use .map() for this.

Here's an example of my code:

import os
import ee
import geemap
import os
out_dir = os.path.join(os.path.expanduser("~"), 'Downloads')
if not os.path.exists(out_dir):
    os.makedirs(out_dir)
Map = geemap.Map()
Map.basemap_demo()
Map

start = ee.Date('2018-01-01')
end = ee.Date('2020-12-31')
LS_collection_initial = ee.ImageCollection("LANDSAT/LC08/C01/T1_SR").filterDate(start, end).filter(ee.Filter.Or(
    ee.Filter.And(ee.Filter.eq('WRS_PATH', 39),
                  ee.Filter.eq('WRS_ROW', 32)),
    ee.Filter.And(ee.Filter.eq('WRS_PATH', 39),
                  ee.Filter.eq('WRS_ROW', 31)))).filter(ee.Filter.lt('CLOUD_COVER', 15)) \
.filter(ee.Filter.calendarRange(4, 10, 'month'))

metadata_col = ee.ImageCollection("LANDSAT/LC08/C01/T1_SR").filterDate(start, end).filter(ee.Filter.Or(
    ee.Filter.And(ee.Filter.eq('WRS_PATH', 39),
                  ee.Filter.eq('WRS_ROW', 32)))).filter(ee.Filter.lt('CLOUD_COVER', 15)) \
.filter(ee.Filter.calendarRange(4, 10, 'month'))

##METHOD FOR MOSAICING BY DATE, MAKES IMAGE ID THE DATE OF IMAGE ACQUISITION
def mosaicByDate(imcol):
    imlist = imcol.toList(imcol.size())
    
    def imdate(im):
        return ee.Image(im).date().format("YYYY-MM-dd")
    
    unique_dates = imlist.map(imdate).distinct()
    
    def dater(d):
        d = ee.Date(d)
        im = imcol.filterDate(d, d.advance(1, "day")).mosaic()##.map(clp)
        return im.set("system:time_start", d.millis(), 
        "system:id", d.format("YYYY-MM-dd"))
    
    mosaic_imlist = unique_dates.map(dater)
    
    return ee.ImageCollection(mosaic_imlist)

LS_collection = mosaicByDate(LS_collection_initial).copyProperties(metadata_col, ['CLOUD_COVER'])

print(LS_collection.size().getInfo()) ##Running this gives an error

I am just starting out with Earth Engine and Python so I apologize if this is a simple problem.

Thanks for your help!

[giswqs]

See https://gist.github.com/giswqs/e85b0371bc3cd15ff6ccd5adfa9643d7

def copyProps(index):
    source = ee.Image(metadata_col.toList(metadata_col.size()).get(index))
    dest = ee.Image(LS_collection.toList(LS_collection.size()).get(index))
    image = ee.Image(source.copyProperties(dest))
    return image

seq = ee.List.sequence(0, LS_collection.size().subtract(1))
final_col = ee.ImageCollection(seq.map(copyProps))

[radwinskis]

Fantastic, thank you for the extremely fast and informative solution! Much appreciated.

[radwinskis]

Hi again, given your solution the metadata copies over perfectly but now only the scene from the metadata collection appears in the final collection.
I'm thinking GEE is possibly using the band dimensions or crs information from metadata_col to bound the image extents and exclude the imagery from WRS_ROW 31. Is there a way to specify just a specific field to copy over, such as cloud cover? I have only been able to figure out how to exclude properties to copy (have tried excluding 'system:footprint' and 'WRS_ROW'), but can't seem to exclude specific band properties that might be causing this.

Definitely going to have to buy you a coffee for your help!

[giswqs]

I might have accidentally flipped the source and dest. It should be dest.copyProperties(source) rather than source.copyProperties(dest). See https://gist.github.com/giswqs/e85b0371bc3cd15ff6ccd5adfa9643d7

def copyProps(index):
    source = ee.Image(metadata_col.toList(metadata_col.size()).get(index))
    dest = ee.Image(LS_collection.toList(LS_collection.size()).get(index))
    image = ee.Image(dest.copyProperties(source, properties=["CLOUD_COVER", "SENSING_TIME"]))
    return image

final_col = ee.ImageCollection(seq.map(copyProps))

[radwinskis]

Yup that was it and your new solution is providing me with exactly what I needed. So awesome! I had noticed that source and dest were possibly swapped but trusted your syntax haha

Thanks Qiusheng!

[giswqs]

I can be wrong sometimes. Sorry for the confusion. Glad to know that it worked.

Thank you for your coffee!