# Why are Nowcasting SAF daytime products apparently truncated at solar angles of 20° (rather than the documented 10°)?

This image shows the Nowcasting Satellite Application Facility (NWCSAF) Cloud Liquid Water Path (LWP) product for 2020-01-08T12:00:00Z:

Cloud LWP from NWCSAF. Source: NWCSAF.

The Algorithm Theoretical Baseline Document (ATBD; PDF, 5.9 MB) divides the full disc into the illumination regimes night, twilight, and daytime by their solar elevation, defining daylight as a solar elevation of larger than 10° (ATBD, Table 3 on Page 14). In the same document, §5.2.1.2.4 describes products only calculated in daytime conditions, including the LWP pictured above. But in the image, the retrieval appears to only include elevation angles larger than around 20° (at noon UTC, near the prime meridian, it reaches about 48°N).

Why do the data appear not to extend to solar elevation angles down to 10° such as documented, but rather truncate at around 20°?

• I have asked this question to the NWCSAF helpdesk (and meanwhile found the relevant configuration/input files in the source code configuration).
– gerrit
Jan 10 '20 at 13:49