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I would like to use JAXA/ALOS/PALSAR/YEARLY/SAR_EPOCH' V2 for HH HV backscatter values and have tried to use epoch band to display date of observation using:

var obsdate = data.select('epoch')

I was hoping that the inspector tool provide data for the difference in days between 2014-05-24 and the observation date.

Has anyone used the epoch band to provide observation date?

1 Answer 1

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From the band description, I understand that in the raw data, the date band corresponds to the difference in days between the date the image was acquired and the date 2014-05-24. The epoch band corresponds to the number of milliseconds since midnight on January 1, 1970, UTC.

To obtain the date of the observation at a specific location, you can use the following strategy:

var data = ee.ImageCollection('JAXA/ALOS/PALSAR/YEARLY/SAR_EPOCH');

// Example location.
var pt = ee.Geometry.Point([-57.56, 0.04]);

var getDate = function (pt) {
  var epoch = ee.Image(data.first()).select('epoch');
  var sample = epoch.sample({
    region: pt, 
    scale: epoch.projection().nominalScale(),
    dropNulls: false,
    geometries: false
  });
  
  sample = ee.Feature(sample.first());
  
  var date = sample.getNumber('epoch');
  date = ee.Date(date);
  
  return date;
};

var date = getDate(pt);

print(date); // Output: Date (2015-12-18 00:00:00)

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