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GRIDDING & BETA CORRECTION

Understand the concepts of gridding in meteorology along with beta correction methods for accurate positioning of satellite imagery. Learn about map projections, grid cells, coordinates, and error corrections.

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GRIDDING & BETA CORRECTION

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  1. GRIDDING & BETA CORRECTION 11 May 1999 Meteorological Satellite Analyst SSgt Dave Mayer

  2. Gridding Cont. • -A grid is an array of points. • -Grids are used to record regularly spaced samples over an area. • -When sampling over the surface of the earth a grid is determined by a map projection, a sampling interval, an origin, and the number of rows and columns. • -A map projection is a one to one mapping of points on the curved surface to points on the plane. • -Curved surface is the surface of the Earth and the plane is what we call a "map.

  3. Gridding Cont. • -Coordinates for points on the surface of the Earth are given in latitude and longitude. • -Coordinates in the map plane (x,y) are defined in the usual manner with x horizontal and increasing to the right and y vertical and increasing upward. • -Map transformations are referred to as projections. • -Most Maps are either conformal or equal-area.

  4. Gridding Cont. • A grid coordinate system is map plane with axes parallel to the rows and columns of the grid and units equal to the sampling interval. • A grid cell is the area between grid coordinates. • It might be useful to think of the grid as a map drawn on graph paper.

  5. Gridding Cont. • -Gridding is calculated by the receiver during or after the processing of an image. • -Receiver uses the known (or expected) location of the satellite • -Map projection options using TeraScan. • Albers conic Mercator orthographic • equal area cylindrical Mollweide rectangular • equidistant azimuthal perspective stereographic • Lambert azimuthal polarstereo UTM • Lambert conic polyconic

  6. First rule of gridding: Do not trust the computer-generated overlay … it is entirely dependent on faulty ephemeris! Look for geography and compare with map overlay. Add or subtract as needed GRIDDING ERRORS

  7. Beta Correction • -Final adjustment for center displacement • -Due to distance of the storm from the subsatellite point or because of storm relative motion. • -when upper features are a considerable distance from the subsatellite point, cyclone center appears farther away from the satellite. • -Error is related to viewing angle of the satellite and the height of the cloud features.

  8. -For average tropical cyclones center position should be adjusted -0.05deg latitude for storms 15-25deg from the SST. -0.1deg latitude For storms 30deg latitude or more from the SST. -Corrections are automatically determined by computer at some facilities. Beta Correction Cont.

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