Boots – shoes – and leggings
Patent
1991-06-18
1993-11-16
Black, Thomas G.
Boots, shoes, and leggings
358109, 342356, B64G 136
Patent
active
052629538
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of rectifying images from geostationary meteorological satellites in real time.
BACKGROUND OF THE INVENTION
The geostationary meteorological satellites that are currently in orbit (i.e. satellites orbiting at about 36,000 km above the Earth over the Equator and having an orbital period of 24 hours so that they are always over the same point on the Earth and appear to be stationary in the sky) are the European satellite METEOSAT, the American GOES satellites, and the Japanese satellite GMS, and they are used for taking meteorological images. All of these use the same principle for scanning the Earth, namely in that lines of data are constructed by each satellite rotating about its own longitudinal axis, which axis is held parallel with the North-South (N-S) axis of the Earth.
No geostationary satellite can be assumed to be in a position which is exactly fixed relative to the Earth: its orbit, its attitude, its speed of rotation, and its scan start point all vary over time relative to ideal values. This gives rise to images which are deformed relative to corresponding reference images as might have been taken under nominal conditions (i.e. absolutely stable conditions).
This situation requires the deformation of the images to be determined with high accuracy and the data relating to the images as transmitted by a satellite and received thereto to be corrected before being used.
With the above-mentioned satellites, such correction can be done only after a complete image of the Earth has been received. In particular, for a satellite such as METEOSAT, this gives rise to a delay before the corrected image can be disseminated to users, which delay may be as much as 40 minutes for the portion of the image which corresponds to the Southern hemisphere and as much as 20 minutes for the portion which corresponds to Europe. Although such delays are theoretically acceptable for meteorologists using the images for the purpose of making conventional weather forecasts over periods of up to one week, they are completely unacceptable for a detailed description of the weather together with forecasts obtained by extrapolation of up to two hours ahead (sometimes called "nowcasting", cf. the definition given by K. A. Browning in the introduction to "Proceedings of the second international symposium on nowcasting" edited by B. Battrick and E. Rolfe, Norrkoeping, Sweden, Sep. 3-7, 1984).
The most relevant prior art relates to the European METEOSAT satellite which is stabilized by spinning about its own axis and which takes one image of the Earth every half hour. Such a period of half an hour between received images is called a "slot". Four images are taken simultaneously, one in the infrared, two in the visible, and one in the water vapor band. A telescope is made to scan through 18.degree. in the S-N direction, giving a full Earth scan of 2,500 lines in 25 minutes. Each of the 2,500 lines constituting the thermal infrared image and the water vapor image has 2,500 picture elements ("pixels"). However, a single visible channel has 2,500 lines of 5,000 pixels each, thus since two visible channels are operated simultaneously, each looking at alternate image lines, a total of 5,000 lines of visible data are available, giving 5,000.times.5,000 pixels per visible image.
The image data is received by the Data Acquisition, Telecommand and Tracking Station (DATTS) from where it is sent to the METEOSAT Ground Computer System (MGCS) located at the European Space Operations Center (ESOC) at Darmstadt, Germany.
The European METEOSAT satellite system has been in operation since Dec. 9, 1977. METEOSAT occupies longitude 0 (Greenwich) above the Equator. Its imaging system always sees the same portion of about 1/3rd of the surface of the Earth. The raw image comes from a radiometer which takes 25 minutes to "sample" the Earth. A system of mirrors splits up radiation into three spectral bands and directs it to three detectors: one of these is sensitive to light (500 nm to 1000 nm), another to infrared ra
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Wolff, "An image geometry model for Meteosat," 1985, Int. Journal of Remote Sensing, vol. 6, No. 10, pp. 1599-1606.
J. Adamson, et al.: "Rectification Quality Assessment of Meteosat Images", ESA Journal 1988, vol. 12, 1988, pp. 467-482.
G. Zhaozeng, et al.: "Geometric Distortion Correction for Satellite Panoramic Picture", Signal Processing IV: Theories and Applications, Proceedings of EUSPICO-88, Grenoble, Sep. 5-8, 1988, vol. III, EURASIP, Elsevier Science Publ. B.V. (NL), pp. 1669-1671.
T. Wolff: "A Simple Approach to Solve the Meteosat Image Deformation Problem Based on Horizon Extraction from Image Data and Orbit Information", Spacecraft Flight Dynamics, ESQ SP-160, Proceedings of an International Symposium, Darmstadt, May 18-22, 1981, pp. 293-298.
Adamson Jan
Bos Albert M.
de Waard Johannes
Agence Spatiale Europeenne
Black Thomas G.
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