I'm wondering if radio waves are reflected by the sea. If so then the usual radar altimeter would work. If not, then is there any other fallback besides barometric altimeter?

According to the wiki article, for some reason radar altimeter uses radio waves (instead of microwaves like usual radar). This is why I put in the radio tag.

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    $\begingroup$ Microwaves are just radio waves in a particular frequency band, and, taken from the Wiki page you linked to: ' Radar altimeters also provide a reliable and accurate method of measuring height above water' $\endgroup$
    – user11357
    Sep 25, 2015 at 4:36
  • $\begingroup$ @Airsick according to the tradition EM spectrum divisions, microwaves and radio waves are separate: en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg $\endgroup$
    – DrZ214
    Sep 25, 2015 at 4:43
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    $\begingroup$ @DrZ214 Which is the problem with over simplistic diagrams. In reality, these boundaries are fairly undefined and microwaves will fall under the category of radio communications for most use cases. $\endgroup$
    – Dan
    Sep 25, 2015 at 7:06
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    $\begingroup$ Note that RADAR is an acronym for "RAdio Detection And Ranging" - so it is no surprise that radar uses radio waves. $\endgroup$ Sep 25, 2015 at 16:29

1 Answer 1


Yes. In the Navy, our primary source of altitude indication under 5,000ft is the radar altimeter. The AGL over the ocean conveniently also happens to be the MSL as well.

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    $\begingroup$ How does AGL always equal MSL, given that the ocean has tides? $\endgroup$
    – Vikki
    May 5, 2019 at 3:12

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