SC
It is called radar altimeter because the operating frequency is in the radar range.
Let's, at least, get this right.
ARINC 707-6 Document Information: Title,
Radio Altimeter. Aeronautical Radio Inc. Publication Date: Oct 30, 1998
And this, typical -
1. PRODUCT OVERVIEW
The ALA-52B Radio Altimeter (RALT), designed and manufactured by Honeywell’s Aerospace Electronics Systems. The ALA-52B RALT, a lightweight, solid-state, airborne altimeter provides accurate digital height measurements above terrain during aircraft approach, landing, and climb-out phases.
The operating range is –20 feet to +8000 feet.
http://www.honeywellcommnav.com/docu...l/52b_tech.pdf