Geostationary Satellite View¶
|Available forms||Forward and inverse, spherical and elliptical projection|
|Implemented by||Gerald I. Evenden and Martin Raspaud|
|+h||Satellite height above earth. Required.|
|+sweep||Sweep angle axis of the viewing instrument.
Valid options are
|+lon_0||Subsatellite longitude point.|
The geos projection pictures how a geostationary satellite scans the earth at regular scanning angle intervals.
In order to project using the geos projection you can do the following:
proj +proj=geos +h=35785831.0
The required argument
h is the viewing point (satellite position) height above
The projection coordinate relate to the scanning angle by the following simple relation:
scanning_angle (radians) = projection_coordinate / h
Note on sweep angle¶
The viewing instrument on-board geostationary satellites described by this
projection have a two-axis gimbal viewing geometry. This means that the different
scanning positions are obtained by rotating the gimbal along a N/S axis (or
and a E/W axis (or
In the image above, the outer-gimbal axis, or sweep-angle axis, is the N/S axis (
while the inner-gimbal axis, or fixed-angle axis, is the E/W axis (
This example represents the scanning geometry of the Meteosat series satellite.
However, the GOES satellite series use the opposite scanning geometry, with the
E/W axis (
x) as the sweep-angle axis, and the N/S (
y) as the fixed-angle axis.
The sweep argument is used to tell proj.4 which on which axis the outer-gimbal is rotating. The possible values are x or y, y being the default. Thus, the scanning geometry of the Meteosat series satellite should take sweep as x, and GOES should take sweep as y.