Satellite projections used in the Dundee Satellite Station include:

Satellite View

This is the view as seen from the satellite's scanner as it orbits the earth. Raw image (HRPT) files received from the satellite show the area directly under the satellite (the sub-satellite point) in great detail in the centre. Due to the earth's curvature, points either side of the centre of the image become distorted with a corresponding loss of detail. For example, at the centre of the image, one image pixel is roughly 1 km on the earth's surface, but towards the edge it may be 15 km.

Quicklook projection

Quicklooks show (at reduced resolution) the same as the Satellite View but with a correction for the earth's curvature. The correction takes into account the latitude and altitude of the satellite. Each pixel in the image represents the same distance on the surface of the earth.

Quicklooks and thumbnails use this projection.

Generic Satellite Projection

The generic satellite projection is produced by considering a satellite orbit where both the inclination and the eccentricity are ignored. Ignoring the inclination means that the satellite passes directly over the North and South Poles - usually the orbit is offset at an angle. A zero eccentricity implies a regularly-shaped orbit. In addition it is assumed that the earth has stopped rotating. The effects of the rotation of the earth will be seen later.

An example of this projection can be seen when viewing a prediction (see below) or when using the graphical form of the Pass Database.

Cylindrical Equidistant Projection

The Cylindrical Equidistant projection produces a map where the parallels and meridians (latitude and longitude lines) are straight and equally spaced. It is thus very easy to navigate an image in this projection given the coordinates of the corner points.

An example of this projection can be seen from the close-up image option when viewing a QuickLook directory.

Mercator Projection

The Mercator Projection is similar to the Cylindrical Equidistant Projection but the lines of latitude are spaced further apart the greater the distance from the equator.

Examples

Generic Satellite Projection

1. Satellite Projection 181 2. Satellite Projection 334

The first image is from a satellite passing over Southbound, the second is Northbound. Notice how the `rectangles' are in fact curved because the earth is rotating underneath the orbiting satellite.

Cylindrical Equidistant Projection

1. Cylindrical Equidistant Projection 181 2. Cylindrical Equidistant Projection 334

The interesting point of this projection is that the image spreads out towards the North Pole. This is an artefact of the projection (the North Pole itself actually becomes a line right across the top instead of a single point) showing that the further north the satellite, the further it can see around the earth.

Mercator Projection

1. Mercator Projection 181 2. Mercator Projection 334

Note the exaggerated vertical scale of Greenland in this projection.


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