Chapter 10 — WATCH ROUTINES 



TRACKING OVERLAY— This is a circular 

 transparent disk which is centered at the 

 pole on the tracking board. On this, the sub- 

 point track of the satellite from which data 

 will be acquired is plotted. 



VHRR— Very High Resolution Radiometer. 



VHR— Very High Resolution. 



VISSR — Visible Infrared Spin Scan Radiometer. 



VTPR — Vertical Temperature Profile Radiome- 

 ter. A device which obtains data similar 

 to the radiosonde. 



WEFAX — Weather Facsimile as applied to 

 satellite rebroadcast of ground prepared data. 



Satellite Applications 



Many areas of the earth have no weather ob- 

 serving stations or so few that serious weather 

 disturbances arise and move, undetected, to- 

 ward inhabited regions. This allows conditions 

 to develop to the stage where adequate fore- 

 casting occurs too late to be really effective. 

 In many instances, even the relatively dense 

 continental network of stations is not adequate, 

 particularly when disturbances move in from 

 oceanic or arctic areas where weather observa- 

 tions are not available. The meteorological 

 satellite provides a truly global means of ob- 

 serving a global phenomenon. This feature 

 makes it an ideal meteorological observing plat- 

 form providing real-time data. 



A real-time data system is one which trans- 

 mits data to a recipient continuously as it is 

 acquired by the system instead of saving the 

 data for readout at a later time. As used in 

 this chapter, the term refers to the fact that 

 the satellite transmits meteorological data to 

 the ground receiving equipment as soon as it 

 senses them Instead of storing them on tape 

 for later readout. 



The most commonly used satellite real-time 

 data system is the SR Scanning Radiometer 

 which acquires and transmits data during both 

 the daylight and dark portions of the orbit. 



SR SYSTEM. — The SR system for real-time 

 transmission consists of sensors that measure 

 radiation in the visual and infrared regions 

 of the spectrum. The reflected light and radiated 

 temperature values are converted to electronic 

 signals which are then converted to cloud-type 

 pictures by the ground receiver. 



As the spacecraft moves along its orbit, the 

 radiometer scans the earth's surface from 



horizon to horizon, essentially perpendicular to 

 the orbital track. The scan across the track 

 is generated by a mirror continuously rotating 

 (through 360 degrees) and reflecting energy to 

 the sensor. Data as sensed are converted to 

 electrical signals which are transmitted in real- 

 time. 



Satellite Expansion 



The meteorological satellites are continuously 

 becoming more versatile through the addition 

 of new and improved detection devices, as in 

 the case of the more improved radiometers. 

 Other improvements include picture quality 

 through improved technology, magnetic tape stor- 

 age, and more advantageous orbital positions. 

 These continue to provide advancement in the 

 field of satellite expansion. 



There are many other meteorological uses 

 being developed along with research in other 

 scientific fields. These research projects are 

 described in many available NASA and NOAA 

 papers and are too lengthy for discussion in 

 this manual. 



Meteorological satellites have come a long 

 way since the launch of the first experimental 

 TIROS satellite. The United States presently has 

 satellites in operational use that are capable 

 of transmitting meteorological information by di- 

 rect readout to ground stations. These are the 

 ITOS/NOAA, SMS/GOES, and the DMSP. A brief 

 description of each of these satellite systems 

 and their capabilities follows: 



ITOS/NOAA. — These sun-synchronous satel- 

 lites, which are in near polar orbit, carry 

 three subsystems for acquiring data which is 

 stored or transmitted in real-time to readout 

 stations. These systems are the SR, VHRR, and 

 VTPR, all of which operate both during the 

 day and night. However, only the SR data is 

 capable of being received by the worldwide 

 low-cost network of ground receiving stations. 

 Only a few elaborate and expensive stations 

 are capable of receiving the VHRR and VTPR 

 data. 



SMS/GOES. — The current series of geo- 

 stationary satellites for meteorological data 

 acquisition and relay are capable of both 

 WEFAX and VISSR imagery. The receipt of 

 WEFAX can be accomplished by existing ground 

 stations after a minor modification to the re- 

 ceiver, but the VISSR data requires extensive 

 and complex equipment. 



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