Top Document: Satellite Imagery FAQ - 3/5 Previous Document: Orbits Next Document: How can I assess my results? See reader questions & answers on this topic! - Help others by sharing your knowledge How is satellite data recieved on the ground? _Intro to Ground Recieving Stations contributed by Peter Bolton <pbolton@clyde.pc.my>_ 1. GROUND RECEIVING STATIONS This document is an introduction to Ground Receiving Station (GRS) acquisition and processing of remote sensing satellites data such as SPOT, LANDSAT TM and ERS-1 SAR. Ground receiving stations regularly receive data from various satellites so as to provide data over a selected areas (a footprints approximately covers a radius of 2500 km at an antennae elevation angle of 5 degrees.) on medium such as computer tape, diskette or film, and/or at a specific scale on photographic paper. GRS are normally operated on a commercial basis of standard agreements between the satellite operators and the Governments of the countries in which they are situated. Subject to the operating agreements, local GRSs sell products adapted to end users needs, and provide remote sensing training, cartography, and thematic applications. 2. GROUND RECEIVING STATION ARCHITECTURE A Ground Receiving Station consists of a Data Acquisition System (DAS), a Data Processing (DPS) and a Data Archive Center (DAC). 2.1. DATA ACQUISITION SYSTEM DAS provides a complete capability to track and receive data from the remote sensing satellite using an X/S-band receiving and autotracking system on a 10 to 13meter antenna in cassegranian configuration. DAS normally store fully demodulated image data and auxiliary data on High Density Digital Tapes (HDDTs). However, in one small UNIX based system, data storage can be stored directly on disk and/or electronically transmitted to distant archives. 2.2. DATA PROCESSING SYSTEM DPS keeps an inventory of each satellite pass, with quality assessment and catalog archival, and by reading the raw data from HDDTs, radiometrically and geometrically corrects the satellite image data. 2.3.DATA ARCHIVE CENTRE The Data Archive closely related to DPS offers a catalog interrogation system and image processing capabilities through an Image Processing System (IPS). 3. GROUND RECEIVING STATION PRODUCTS The GRS products can either be standard or value added products. Both are delivered on Computer Compatible Tapes (CCTs), CD ROM, cartridges, photographic films or photographic paper prints at scales of 1:250 000, 1:100 000, 1:50 000 and 1:25000. i. Standard products - SPOT-1 and 2/HRV : data of CNES levels 0, 1A, 1B, 2A - Landsat TM : data of LTWG levels 0, 5, - ERS-1 SAR : Fast Delivery and Complex products. ii. Value added products - For SPOT . P + XS : Panchromatic plus multi-spectral, . SAT : a scene shifted along the track, . RE : a product made of 2 consecutively acquired scenes, . Bi-HRV : Digital mosaic produced by assembling 2 sets of 2 scenes acquired in the twin-HRV configuration. . Stereoscopy : Digital terrain model (DTM) generation, . Levels 2B, S and level 3B using DTMs. - For Landsat TM: levels 6, S and 7. - For ERS-1 SAR : geocoded data. - For any instrument: . Image enhancement and thematic assistance, . Geocoded products on an area of interest defined by the customer (projection, scale, geocoding and mosaicking according to the local map grid). 4. GROUND RECEIVING STATION OPERATION Persons needing images for thematic applications in the field of cartography, geology, oceanography or intelligence, etc, will refer to the station catalog in order to find out if the data are available over the area concerned. There are two possibilities : The data exists. The customer fills in a purchase order and is then provided with the product on a medium such as CCT, film or paper print. If the data are available in the GRS catalog, a list of the related scenes and their hardcopies (named "quick looks") are provided. The data does not exist. a) For SPOT, the customer fills in a programming request form which is sent by GRS to the Mission Control Centre (MCC) in Toulouse, France. MCC returns a Programming Proposal to be submitted for approval. Upon approval, the confirmation is returned to MCC which in turn sends a programming order to the satellite for emitting the data during its pass over the GRS antenna. At the same time, MCC sends to GRS, the satellite ephemerides for antenna pointing and satellite tracking. In the case of SPOT, if the data does not exist within the Station catalog but are listed in the SPOT IMAGE worldwide catalog, GRS may request the level O product from SPOT IMAGE in TOULOUSE in order to process it locally. b) For other sensors, LANDSAT TM or ERS-1, the satellite ephemerides are known at GRS and the antenna is pointed accordingly in order to track all selected passes. Within the GRS, the raw satellite data are received by the Data Acquisition System (DAS), and recorded on High Density Digital Tapes (HDDTs). HDDTs are then sent to the Data Processing System (DPS), where an update of the Station catalog is made as well as a quick look processing. DPS is also in charge of automatic processing of selected raw data in order to produce images of standard level. Value added products with cartographic precision are produced within DPS using interpretation workstations which must be part of an operational Geographic Information System (GIS) combined to an Image Processing System (IPS). Once processed, the data, on CCT, are sent to the Data Archive Center (DAC) where they are delivered to the customers after a quality checking. At DAC, further processing may be applied to the data such as image stretching, statistical analysis, DTM, or a conversion from tape to film and paper prints in the photographic laboratory; "customized services" may also be offered. _________________________________________________________________ Image Interpretation User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: Satellite Imagery FAQ - 3/5 Previous Document: Orbits Next Document: How can I assess my results? 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Last Update March 27 2014 @ 02:12 PM
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