



4.2.1 Geometry Glossary
Table 4.2  Geometry Glossary.
azimuth angle

Horizontal direction measured clockwise from the meridian plane.

elevation

The vertical distance of a point or object above or below a reference surface or datum (usually mean sea level). Also referred to as altitude or height.

geodesy

Science concerned with the measurement and mathematical description of the size and shape of the earth and its gravitational fields. Geodesy also includes the largescale, extended surveys for determining positions and elevations of points, in which the size and shape of the Earth must be taken into account.

geoid

Figure of the Earth visualised as a mean sea level surface extended continuously through the continents. It is a theoretically continuous surface that is perpendicular at every point to the direction of gravity (the plumb line).

latitude

Angular distance, in degrees, minutes, and seconds of a point north or south of the Equator.

longitude

Angular distance, in degrees, minutes, and seconds, of a point east or west of the Greenwich meridian.

nadir

Point on the ground directly in line with the remote sensing system and the centre of the Earth.

pointing direction

Angle between a look direction lying in the (Y_{S}=0) plane in the satellite fixed coordinates system, and the Z_{S} axis of that system. Positive around Y_{S}.

satellite fixed coordinate system

Z_{S} points in the direction of the Earth outward local normal. X_{S} is perpendicular to the satellite orbit plane. Y_{S} completes the righthanded system and is the direction of the opposite of the satellite velocity. This coordinate system is defined and referred to as the "Satellite Relative Actual Reference" system.

Sun zenith angle

The vertical direction of the Sun relative to the zenith expressed in degrees.

viewing angle

The angle measured from a position on the earth ellipsoid pointing towards the satellite. It is defined by its zenith and azimuth angles as shown in the following diagram:

WGS84 geoid

The Earth geoid model referred to as a "reference ellipsoid".

zenith angle

Angle between a look direction in the topocentric coordinate system and the zenith axis of that system (zenith angle + elevation angle = 90°).




 
Keywords: ESA European
Space Agency  Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,
atmospheric chemistry
