SPOT Twin Imaging System (39 kb)
The SPOT Program supports commercial remote sensing on an international scale, establishing a global network of control centers, receiving stations, processing centers, and data distributors. The French space agency, Centre National d'Etudes Spatiales (CNES), owns and operates the SPOT satellite system while worldwide commercial operations are anchored by private companies (i.e., SPOT IMAGE Corporation in the United States, SPOT IMAGE in France, SATIMAGE in Sweden, and distributors in over 40 countries).
The SPOT satellites carry two High Resolution Visible (HRV) sensors, two high density tape recorders, and a telemetry transmitter. The HRVs, constructed with multilinear array detectors, operate in a cross-track direction. Operating independently of each other, the two HRVs acquire imagery in either multispectral and/or panchromatic modes at any viewing angle within plus or minus 27 degrees. This off-nadir viewing enables the acquisition of stereoscopic imagery.
The SPOT system provides global coverage between 87 degrees north latitude and 87 degrees south latitude. Each nominal scene covers a 60- by 60-km area.
Carrying HRV sensors that operate in either single or dual mode, the SPOT satellites maintain a near-polar, near-circular, Sun-synchronous orbit with a mean altitude of 832 km (at 45 degrees north latitude which corresponds to continental France), an inclination of 98.7 degrees, and a mean revolution period equaling 101.4 minutes. The SPOT satellites orbit the same ground track every 26 days with a nominal cycle of 369 revolutions. Crossing the equator from north to south at 10:30 a.m. mean local solar time, the satellites' reference tracks are 108.6 km apart. The reference tracks draw closer at higher altitudes.
SPOT Twin Imaging System (39 kb)
Each HRV sensor views a 60-km area, and together they view a 117-km area with 3-km overlap.
Characteristics of Multispectral Panchromatic SPOT HRV Instruments Mode (XS) Mode (P) ____________________ _____________ ____________ Instrument Field Of View: 4.13 degrees 4.13 degrees Ground Sampling Interval: 20 m by 20 m 10 m by 10 m (Nadir Viewing) Pixels Per Line: 3000 6000 Ground Swath Width: 60 km 60 km (Nadir Viewing)The SPOT data are transmitted in direct mode or recording mode to ground receiving stations (SPOT's worldwide ground-station network comprises 16 direct receiving stations). Data transmitted in direct mode are received in real time during daytime passes. Data transmitted in recording mode (i.e., via on-board tape recorders) are received during nighttime passes by SPOT's main receiving stations in Toulouse, France, and Kiruna, Sweden.
In addition to SPOT's two main receiving stations, the SPOT worldwide ground-station network is comprised of 14 direct receiving stations:
Operator Location Commissioned Operator
________ ________ ____________ ________
Canada Prince Albert June 1986 CCRS
Canada Gatineau June 1986 CCRS
Spain Maspalomas November 1987 ESA
(Canary Is.)
Brazil Cuiaba April 1988 INPE
Thailand Lad Krabang May 1988 NRCT
Japan Hatoyama October 1988 NASDA
Pakistan Islamabad June 1989 SUPARCO
South Africa Hartebeesthoek August 1989 CSIR
Saudi Arabia Riyadh October 1990 KACST
Australia Alice Springs May 1990 ACRES
Israel Tel Aviv February 1991 ISA
Ecuador Cotopaxi July 1992 CLIRSEN
Taiwan Chung-Li July 1993 CSRSR
Indonesia Parepare October 1993 LAPAN
SPOT Receiving Station Coverage
Areas (33 kb)
For more information on SPOT's commercial network, see the SPOT IMAGE Homepage at one of the following sites:
The SPOT images undergo preprocessing operations (for SPOT data, the term "processing" is used only in terms of data manipulations undertaken by end-users).
The data transmissions are demodulated, synchronized (the 8-GHz carrier is filtered out), and simultaneously recorded onto two high-density data tapes (HDDTs). One of the HDDTs is used as an archive master while the other HDDT acts as a backup for the master tape. Archiving and inventorying operations include:
*A SPOT satellite data-collection pass lasting approximately 10 minutes with a constant viewing configuration yields two data segments with each segment containing approximately 75 scenes. This yield represents use of either one HRV set to dual mode or use of both HRVs in single mode. The size of individual scenes varies (i.e., a vertically viewed scene has a 60- by 60-km scene size while an obliquely viewed scene at maximum has a 60- by 81-km scene size).
The SPOT raw data archive does not undergo additional preprocessing until a user request generates a requirement for the data. Standard preprocessing includes both geometric and radiometric corrections. Five standard preprocessing levels are available to the user:
Oblique images with a line sampling interval greater than 10 meters in the panchromatic mode and 20 meters in the multispectral mode are resampled at 10 meters and 20 meters, respectively.
The raw data are decompressed, corrected, and recorded onto CCTs, which serve as end products. The CCTs also are used for producing full-resolution photographic films (also called precision films).
Spatial Resolution
Mode Band Resolution
____ ____ __________
Multispectral (XS) 1 (Green) 20 meters
2 (Red) 20 meters
3 (Near Infrared) 20 meters
Panchromatic (P) Not Applicable 10 meters
Launch Decommission Satellite Date Date _________ ______ ____________ SPOT 1 2/22/86 12/31/90 SPOT 2 1/22/90 SPOT 3 9/26/93 SPOT 4 Anticipating launch in 1997. SPOT 5 Anticipating launch in 2001.
Mode Band Micrometers
____ ____ ___________
Multispectral (XS) 1 (Green) 0.50-0.59 micrometers
2 (Red) 0.61-0.68 micrometers
3 (Near Infrared) 0.79-0.89 micrometers
Panchromatic (P) Not Applicable 0.51-0.73 micrometers
Micrometers and their relationship to the electromagnetic spectrum are explained in the glossary.
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-interleaved-by-line (BIL) 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.
Additional information on the organization of SPOT data follows:
Data are available through SPOT distributors (listings available through SPOT's Homepage sites).
To place orders and to 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:
Online requests for these data can be placed via the USGS Global Land Information System (GLIS) interactive query system. The GLIS system contains metadata and online samples of Earth science data. With GLIS, you may review metadata, determine product availability, and place online requests for products.
Data and imagery are available in a variety of processing levels and scales. Standard products include:
SPOT Band-2 Multispectral Scene (33 kb)
The SPOT Image Corporation has made over one gigabyte of sample SPOT data available via an anonymous File Transfer Protocol (FTP) account at the EROS Data Center. Users of these data are bound by the stipulation detailed below. All questions concerning these data should be directed to:
SPOT Image CorporationUse Stipulation:This imagery is for demonstration purposes only and cannot be reproduced, sold, or further distributed without written permission from SPOT Image Corporation. For information, contact:
SPOT Image Corporation
Anonymous FTP Connection to SPOT Data Samples
Applications and Related Data Sets
Following are some SPOT data applications and their respective disciplines:
Permission has been granted to the EROS Data Center by SPOT Image Corporation to provide sample SPOT data via anonymous FTP; to display a sample SPOT scene and graphics; and to use the SPOT logo as an icon in components of the Global Land Information System (GLIS).
Information from SPOT publications and the SPOT Homepage have also been used in the construction of this GLIS guide (see References).
[Copyright CNES/SPOT Image Corporation, 1995].
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 (see Processing Steps).
The GRS indicates the nominal location of scenes that can be acquired within SPOT's twin-vertical viewing configuration area (between 87 degrees north latitude and 87 degrees south latitude). 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 pattern of nodes within the three zones is defined in terms of satellite viewing conditions corresponding to the twin-vertical viewing configuration. This pattern indicates the nominal location of scene centers yielded by the viewing configuration. With oblique viewing, scene centers are always located on the J row, but scene centers may not coincide in longitude with GRS nodes.
The K columns are derived directly from the SPOT reference tracks. Each track number (N) corresponds to two K columns:
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.
GRS/Twin-HRV Configuration (8 kb)
Information on SPOT data distributors is available through the SPOT IMAGE Homepage at the following sites:
The Logical Volume is a set of files containing all data that correspond to a particular product. These files may be stored on one or more CCTs. The files in a single SPOT CCT Logical Volume include:
The files are separated by end-of-file (EOF) tape marks. The Null Volume Directory file is followed by three EOFs designating an end of set.
The SPOT files consist of sets of physical records separated by inter-record gaps on the CCT (see the Logical Volume table for the number of records and record lengths per file).
Imagery records can have one of four fixed lengths depending upon the length of the image line:
3,960 bytes (split-record size option*)
5,400 bytes (line length < 5,300 pixels)
8,640 bytes (5,301 < line length < 8,450 pixels)
10,980 bytes (8,451 < line length < 10,880 pixels)
As the first file on any SPOT CCT, the Volume Directory file contains information about the logical volume (e.g., format structure, tape contents). The Volume Directory file consists of five 360-byte records:
The Volume Descriptor record identifies the logical volume within a volume set and the number of files on the volume. The Volume Descriptor record also contains identifying information concerning the CCT and the recording format. Each Pointer record references one of the three data files in the logical volume and identifies the data file recording format. The Text record contains information about the creation of the tape and information on CCT identification.
The Leader file contains auxiliary information related to the SPOT scene (e.g., identification parameters defining the geometry and the radiometry of the scene, preprocessing data). The Leader file consists of twenty-seven 3,960-byte records:
The Imagery file contains a File Descriptor record and Image Data records. The number of records in the Imagery file is contingent upon: (1) the number of spectral bands as determined by the multispectral or panchromatic modes; (2) the number of image lines as determined by the level of preprocessing; and (3) the file option in which users may request that the image data be split into records with nonstandard lengths. The File Descriptor record in the Imagery file may be repeated on each physical volume in the case of multi-volume scenes.
The variable segment of the Imagery Descriptor record contains information on the number of and the length of imagery records; on how the image pixels are packed; on left- and right-margin locations; and on size of the prefix and suffix data. Values range between 1 and 255 for each pixel. A zero pixel count corresponds to a nonsignificant radiometric value and is reserved for margins around the imagery data, for level 1A bad data lines, and for dead detectors.
The Trailer file contains information on image data quality and on the geometric models used for certain preprocessing operations. The Trailer file consists of three or more 1,080-byte records:
The Null Volume Directory file indicates the end of the logical volume and consists of one 360-byte Volume Descriptor record. Using the same file structure, the Volume Descriptor record in the Null Volume Directory file contains a subset of the information found in the Volume Descriptor record in the Volume Directory file. The Null Volume Directory file is the last file recorded on a digital SPOT scene and is followed by three end-of-file (EOF) markers denoting the end of set.
SPOTView products include digital orthoimagery and image maps produced from SPOT satellite raster image data. These products are produced for use in image processing, for use with geographic information systems and cartographic automatic mapping software, and for use with other computerized mapping systems. The SPOT imagery are geocoded to a map projection of the user's choice, are ortho-corrected, and can be distributed in several file formats.
For more information on SPOTView, contact:
SPOT Image CorporationU.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. --------------2ADA66CC61B6--