I am using Google Earth Engine to compute NDWI time series, in particular by plotting "Landsat 7 Collection 1 Tier 1 8-Day NDWI Composite" data values
The product description says:
These Landsat 7 Collection 1 Tier 1 composites are made from Tier 1 orthorectified scenes, using the computed top-of-atmosphere (TOA) reflectance.
It is derived from the Near-IR band and a second IR band, ≈1.24μm when available and the nearest available IR band otherwise.
This seems strange to me, since Landsat 7 has no 1.24μm band, but only a SWIR band at 1.55-1.75 μm https://landsat.usgs.gov/what-are-band-designations-landsat-satellites
How does the Google algorithm calculates it?