Correctly drop one field instead of deinterlacing in ffmpeg

So, I have a 1920x1080 interlaced video recording. I want to recode using ffmpeg to procuce a 960x540 non-interlaced video. And ideally I'd like to avoid deinterlacing - instead I just want to drop one of the fields seeing I only need half the lines anyway. But I could not find the filter to do this. So, how do I drop one of the fields, getting the remaining field at 1920x540? (Which I can then resize to 960x540).