The organization of SPOT data is dependent upon the number of volumes as determined by the imaging mode, viewing angle, and level of processing. Because of its levels of processing and geometric correction, a SPOT scene may vary in size from approximately 27 megabytes to approximately 100 megabytes. A panchromatic SPOT scene is a single-band image while a multispectral scene consists of 3 bands organized in a band-sequential format.

Image data are recorded such that the first pixel corresponds with the extreme northwest corner of the scene. Succeeding pixels correspond first to those pixels immediately east of the first pixel and then correspond line by line from north to south. Regardless of spectral imaging mode or level of processing, all image data are recorded as right-justified, 8-bit pixels.

Data are available through SPOT distributors (listings available through SPOT's Homepage sites).

To place orders outside of Earth Explorer and/or obtain additional information regarding technical details, ancillary products, and pricing schedules, contact a SPOT data distributor. Information on SPOT data distributors is available through the SPOT IMAGE Homepage at the following sites:
Reston, Virginia, U.S.A. at: http://www.spot.com/
Toulouse, France at: http://www.spotimage.Fr/

Data and imagery are available in a variety of NLAPS recipes and standard products include:

• Computer compatible tapes [8-mm digital audio tapes (DAT), 4-mm DAT]
• CD-recordables
• FTP

• Copyright Information
• Grid Reference System (GRS)

Grid Reference System (GRS)
The SPOT Grid Reference System (GRS) is used to identify the geographic location of SPOT images. The grid is made up of nodes located at the intersection of columns (K) and rows (J). When data strips are split into scenes, the SPOT GRS links each scene with two K,J designators representing a GRS node. Once the K,J designators have been identified for a new scene, the designators are added to that scene's characteristics file.

The GRS indicates the nominal location of scenes that can be acquired within SPOT's twin-vertical viewing configuration. In the case of oblique viewing, the scene centers do not normally coincide with the GRS nodes as defined by the surveying conditions of twin-vertical viewing. Therefore, any SPOT scene acquired in the oblique viewing mode is identified by the K,J designators of the node closest to the scene center.

The GRS divides the Earth into five zones forming a symmetrical pattern on either side of the Equator. This division is dictated by the satellite's orbital characteristics and, more specifically, by the convergence of the ground tracks at high latitudes.

• The intermediate zone extends from 51.5 degrees north latitude to 51.5 degrees south latitude.
• The north and south zones extend from 51.5 degrees to 71.7 degrees north or south latitudes, respectively.
• The north and south polar zones extend from 71.7 degrees to the pole north or south latitudes, respectively.

The K columns are derived directly from the SPOT reference tracks. Each track number (N) corresponds to two K columns:
K = 2N-1 associated with HRV-1 and located west of track N (odd number)
K = 2N associated with HRV-2 and located east of track N (even number)

The distance between these two columns (i.e., between K=2N-1 and K=2N) is constant at about 58 km and is a direct result of the twin-vertical viewing configuration.

Since the GRS nodes are located on either side of the reference tracks, the scene centers obtained in vertical viewing do not coincide with the GRS nodes.

The J rows correspond to latitude lines (i.e., all GRS nodes at the same latitude share the same J designator). The interval between the rows has been calculated to ensure that minimum endlap occurs between two successive scenes. The scenes of a given data strip are segmented in such a way that the scene centers are located on two adjacent rows (J and J+1).

In the two polar zones, the GRS node pattern is independent of satellite orbital and viewing characteristics. The pattern is obtained through hexagonal dissection using quasi-equilateral triangles, where the triangle measures approximately 26 km to a side.

U.S. Geological Survey Disclaimer: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.