Missing SRTM files on the FTP server

S1TBX is unsuccessfully trying to download SRTM files, showing the message below. We have checked the FTP server xftp.jrc.it and the files actually do not exist. What is wrong here?

ftp retrieving /pub/srtmV4/tiff/srtm_37_12.zip
error code:550 on /pub/srtmV4/tiff/srtm_37_12.zip
ftp retrieving /pub/srtmV4/tiff/srtm_36_13.zip
error code:550 on /pub/srtmV4/tiff/srtm_36_13.zip
ftp retrieving /pub/srtmV4/tiff/srtm_37_13.zip
error code:550 on /pub/srtmV4/tiff/srtm_37_13.zip

SRTM only has tiles over land. The software doesn’t have a master index of which tiles exist so it tries to download a tile based on the lat lon. If it doesn’t exist, it fills the dem with no data value.

Thanks for the clarification! That confirms our suspicions.

I am currently encountering a similar problem. However, this time the SRTM files do in fact exist. The error message in my logs reads as follows:

Error! S1A_IW_GRDH_1SDV_20150528T180750_20150528T180815_006125_007F1C_025F.zip (False, 'xftp.jrc.it: unknown error\nhttp retrieving http://droppr.org/srtm/v4.1/6_5x5_TIFs/srtm_35_01.zip\nxftp.jrc.it\nhttp retrieving http://droppr.org/srtm/v4.1/6_5x5_TIFs/srtm_36_01.zip\n')

The http links inside the error messages exist but obviously s1tbx can’t resolve them. Does anyone have an idea what is going on? Currently my only alternative is downloading all the DEMs and configuring s1tbx to use them as external DEMs. However, I hope there is a simpler solution.