Satellite photogrammetry
The Satellitenfotogrammetrie is a method for precise photographic observation of artificial satellites . It was developed around 1955 - a few years before space travel - from the experience of astrometry and between 1960 and 1980 led to the first heyday of satellite geodesy , in particular
- to the first international measurement campaigns for the European network
- to the North American base network of the North American Datum (NAD)
- to the first global surveying network , the world network of satellite triangulation (1973/74)
- to combine geometric methods with Doppler satellites (175)
- and to a determination of the mathematical figure of the earth completely independent of other methods ( earth polyhedra and first global geoid determination ).
The satellites can be photographed with cameras of three types:
- Fixed ( Altaz -mounted) or ballistic cameras like the well-known Wild BC-4 : Here, the stars are shown as short line tracks, whereas the earth satellites are long tracks.
- For precise time measurement (at least 0.001 sec), fine time stamps are imprinted on the photographed line traces with a quartz-controlled rotary shutter .
- Parallactic or equatorial mounting , especially for the astrographs initially used in observatories : the stars appear point-like, all other objects as short to long tracks.
- In astronomy, this technique is used - with two time-shifted recordings - among other things to discover and measure asteroids (minor planets) and comets . Even very weak celestial bodies can be recognized by their orbital movement in double images with a blinking comparator .
- multi-axis mounted satellite cameras , e.g. B. the English Hewitt or the American Baker-Nunn camera : they are tracked to the satellite sought, but whose orbit elements must be known approximately. The satellite becomes a short line track, the star background a system of long tracks.
Today, photographic direction measurement has taken a back seat compared to other methods such as GPS , interferometry or electronic distance measurement with lasers.
The evaluation of the photo plates or the digital images is carried out on the stereo comparator or by semi-automatic software (editable on the screen) . The coordinate transformation between the measurement images and the system of star locations takes place either according to the astrometric or the photogrammetric method. The first uses affine or polynomial relationships, while the second group of methods models the optical beam path .
See also: