I'm looking at the Hansen forest loss v1.5 data in Earth Engine. According to the Hansen documentation,
In addition, to reduce confusion, beginning with version 1.4 we are no longer releasing loss as a separate layer from lossyear. Loss as previously releaed corresponds to nonzero values of loss year. (link)
If I understand correctly, this means that the
loss band is deprecated, and only the
lossyear band should be used. However, the Hansen v1.5 data in Earth Engine still has a
loss band (link). Furthermore, there are pixels where the
loss band is equal to 1 (indicating a loss has occurred), but the
lossyear band is equal to 0 (indicating that no loss has occurred) (see example script in Earth Engine).
What is the cause of this discrepancy? In the pixels where
loss == 1, but
lossyear == 0, are those pixels that were classified as loss in the last year that Hansen used the
loss pixel, but in subsequent versions have not been classified as loss? It seems like this might be the case, as version of Hansen prior to 1.4 do not seem to have this discrepancy (see example script).
Possibly related: there appears to be a typo in the Earth Engine documentation for the Hansen dataset. According to the EE docs, forest loss is represented by the
lossyear band, and is "Encoded as either 0 (no loss) or else a value in the range 1–16, representing loss detected primarily in the year 2001–2017, respectively" (link). I don't think I'm totally losing my mind: there are sixteen numbers in the range 1-16, but 17 numbers in the range 2001-2017. (Right?)
I'm inclined to assume that the
loss band is legacy and only
lossyear should be used, except that the Hansen forest loss Earth Engine app and an example in the Earth Engine code playground both treat a 0
lossyear value as a loss in the year 2000, instead of no loss, as described by the Hansen documentation. I'm pretty sure the EE app was produced by the UMD team, making things more unclear. (EE App, EE example script).