Altimeter

{
  "id": "MLC-T-ENV-001219",
  "term": "Altimeter",
  "field": "Environment",
  "definition": "1. An active instrument (see active system) used to measure the altitude of an object above a fixed level. For example, a laser altimeter can measure height from a spacecraft to an ice-sheet. That measurement, coupled with radial orbit knowledge, will enable determination of the topography.\n\n2. Instruments for measuring elevation. Space-borne Altimeters onboard satellites measure sea surface height relative to the marine geoid (a gravitational equipotential surface) or a mean sea surface (MSS) constructed from years of historical altimetry data. The fundamental principle of altimetry is simple: send a radar pulse from the satellite to the sea surface, and record when the reflected signal returns to the satellite. The measured round trip travel time is converted to range (distance between the altimeter and the sea surface) by dividing by two (to convert to one-way travel time) and dividing by the speed of light (to convert time to distance).",
  "references": [
    "NASA Earth Observatory Glossary",
    "John L. Lillibridge, III (NOAA/NESDIS Laboratory for Satellite Altimetry), quoted at Ocean Current Glossary, Physical Oceanography Jargon, and a Good Place to Start Reading, at http://oceancurrents.rsmas.miami.edu/glossary.html"
  ],
  "url": "https://mlchart.com/terminology/environment/altimeter/"
}