As far as I know, in SH4, a radar report is a radar report. It won't tell you which one. If you have contacts on, you can peek at the map and see what it is. If you have contacts off, you can take a look at the radar yourself, and look for a surface contact, but at extremely long ranges, the blip is off the screen.
I got annoyed by this when playing with contacts off, so I created
this to display only aircraft and not ships on the map. Not perfect, but it works well enough for me. If a radar report is announced, I can jump to the map and find out soon enough.