⛰️🔢DTM or DEM (Digital Elevation Model) is an electronic representation of terrain surface. This data consists in elevation values at all intersections (points) of a grid with a specified spacing. Elevations are given in a defined “datum”, or vertical reference system. hashtag#Aeronauticalinformation is supposed to use the standard datum EGM-96, but many countries keep using their own local datum.
ICAO defines 4 types of surfaces to be surveyed, the same for terrain and obstacles:
✅AREA 1: the entire territory of a State;
✅AREA 2: within 45km of an ARP, or within the TMA if there is one;
✅AREA 3: 50m around the aerodrome ground movement area, and 90m around the RWY centre line;
✅AREA 4: only for precision approach CAT II and III, 60m on each side of the RWY centre line, extended over 900m ahead of the THR.
Area 4 is the most expensive data to obtain, but it’s only for less than 59ha if the RWY is 4km long. If you fancy Imperial Units, that’s 145 acres for a RWY of about 20 furlongs (2.15NM). Your main concern might be the cost of closing the RWY🚧 while surveyors perform their work.
Each area comes with its own set of requirements, but this will be for another post: stay tuned! (i.e. follow us!)
🧑✈️ICAO recommends aerodromes to be good neighbours and coordinate the provision of terrain data for adjacent aerodromes, including across political borders.
hashtag#AIMWithNilacandi hashtag#ais2aim
