Glossary of terms
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Glossary of terms


AOS - Acquisition of Signal, when a pass starts.
- Automatic Picture Transmission - the analogue transmission standard used on the 137MHz band from polar orbiting satellites.  A simple omni-directional antenna will pick up these broadcasts.
ASCAT - Advanced scatterometer, an instrument on Metop.
Ascending pass - satellite pass crossing the equator from south to north.
ASL - Above Sea Level, a height in feet or metres.
ATOVS - Advanced TIROS Operational Vertical Sounder.  Data from multi-channel thermal and microwave sensors carried on the polar orbiters.  By providing multiple channels, some information about the profile of atmospheric constituents can be derived.  "Sounder" implies looking into the atmosphere at different depths.
AVHRR - Advanced Very High Resolution Radiometer - the 6-channel imaging instrument carried on the NOAA polar orbiting satellites like NOAA-15 and NOAA-17.  Five of the six channels can be transmitted with HRPT and two channels with APT.



BUFR - Binary Universal Form for the Representation of meteorological data.  BUFR is the name of a binary code for the exchange and storage of data.  See: WMO PDF document.



C-band - satellite TV band with a downlink centred on 4GHz.  Suffers less from rain attenuation than Ku-band, and therefore preferred in tropical regions.  Used for EUMETCast in Africa.
Channel - typically typically on spectral channel (q.v.) derived from detecting radiation at a certain well-defined wavelength.  The 12 Meteosat-8 channels are described here.
CLASS - Comprehensive Large Array-data Stewardship System.  An electronic library of NOAA environmental data.



Descending pass - satellite pass crossing the equator from north to south.
DVB - Digital Video Broadcasting.  A standard for video broadcasting with variants for cable (DVB-C), satellite (DVB-S) and terrestrial (DVB-T) methods.  The DVB-S system is used for EUMETCast from the Eurobird-9 satellite.
DVB PCI card - DVB satellite TV and data receiver card, installed inside your computer, used for  EUMETCAST reception.
DVB USB Box - DVB satellite TV and data receiver which is external to (not requiring installation  inside) your computer which plugs into a USB port.



EARS - European ATOVS Retransmission Service.  Service operated by EUMETSAT which takes data from the polar orbiting satellites and broadcasts it over EUMETCast.  This means that you do not need a complex tracking antenna and receiver to receive this data.
Eclipse period - twice a year geostationary satellites have periods in their orbits where the earth eclipses the sun. blocking energy to the solar panels.  The Meteosat Second Generation satellites rely on battery power during this period, but other satellites may have elements switched off to conserve power.  More.
EKU - EUMETSAT Key Unit - a USB-based eToken which plugs into your PC's USB port to allow access to EUMETCast data streams.  You can purchase an EKU from EUMETSAT.
EPS - EUMETSAT Polar System - the "morning" (local time) polar orbit satellite, with the "afternoon" coverage being provided by the US.  The satellite is called Metop.
ESA - European Space Agency responsible for satellite launches.
ESOC - European Space Operations Centre at Darmstadt in Germany.
EUMETCast - system for sending a digital data stream over a DVB link.  Operated by EUMETSAT, the current broadcasts include data from the geostationary Meteosat-8 and GOES satellites, ATOVS data from the polar orbiting satellites, and Rapid Scanning Service data from Meteosat-6.  The different data streams have different PIDs.  An EKU is required to access certain data.
EUMETSAT - European Organisation for the Exploitation of Meteorological Satellites - operator of weather satellites based in Darmstadt, Germany.  Operates Meteosat-5, 6 & 7 and the Meteosat-8 satellites, and allows amateurs and educational users free access to the real-time data.



FTA - Free To Air.  You may have seen this on the TechniSat equipment info sheets - these are unencrypted (DVB) TV channels [Frei-Sat (R) Digital].



GEO - the Group for Earth Observation.
GeoSatSignal - my geostationary satellite data processing program.
Geostationary - satellites with an orbit keeping them at a fixed point above the equator.  This includes many weather and telecommunications satellites.  The orbital height is about 36000km above the earth.
GMS-5 - Japanese geostationary satellite covering Asia and Australasia - replaced by MTSAT-1R.
GOES - Geostationary Operational Environmental Satellite.  The US geostationary satellites managed by NASA and NOAA, comprising GOES-12 at 75W and GOES-10 at 135W covering the continent of America.  They are also providing temporary coverage of Asia/Australia from GOES-9 replacing GMS-5.
GPS - global positioning system, a collection of satellites in 12-hour orbits allowing accurate location and time determination.
GRIB - General Regularly-distributed Information in Binary, a binary data format used for information which is on a grid like a map projection.  See: WMO PDF document.



Hot Bird - a cluster of satellites used for TV transmissions, including the DVB used by EUMETCast.  There are 5 satellites at the 13 degrees East EUTELSAT Hot Bird location - Hot 
Birds 1, 2, 3, 4 & 6. Hot Bird 5 crashed on launch.
- High Rate Information transmission - digital transmission standard for geostationary weather satellites when the data rate exceeds 128Kbit/s.  There is an HRIT data channel on the EUMETCast service.
HRPT - High Resolution Picture Transmission - digital transmission standard for polar orbiting satellites.
HRPT Reader - my HRPT decoding and display program.
HRV - High Resolution Visible channel.  A channel on Meteosat-8 with a broad spectral response providing 1km resolution at the satellite sub-point.  The complete image from the HRV channel would be 11136 x 11136 pixels, but not all of that data can be transmitted.
HRV Window - because all the data from the HRV channel cannot be transmitted with the bandwidth available on the Meteosat-8 satellite-to-earth downlink, only half the available scan width is used.  The portion of the earth where this scan is centred can be varied between the southern and northern parts of the scan.  Typically, the southern part of the scan covers Africa, and the northern part of the scan covers Europe and the Mediterranean.



Inclination - the angle which the satellite's orbit makes to the earth's equator.  Ideally, a geostationary satellite would have an inclination of zero degrees, but in reality towards the end of the satellite's life there is not enough fuel to make the minor orbit corrections required for zero degrees inclination, and the inclination increases.  In June 2004, for example, the inclination of Meteosat-5's orbit was nearly 7.



Kepler data - data describing the orbit of a satellite, whether polar orbiting or geostationary.  As opposed to a precise orbital model, Kepler data is intended to be used around the time that it is measured.  This allows the data and the calculations to be simplified.  Depending on the satellite and your application, the Kepler data (sometime called "Keplers") will be valid for some days or weeks ahead. is a good online source, and you will need to register at Space-Track for access after 2005 April 01.
KOZ - Keep-Out zone
- with GOES satellites, the region where the sun might damage a sensor if the image were allowed to be within the field of view.  More.
- satellite TV band with a downlink centred on 12GHz.  Suffers more from rain attenuation than C-band.  Used for EUMETCast in Europe.


Level-0, level 1,0, level 1.5 - processing levels in satellite data.  Level-0 or level 1.0 usually refers to the raw satellite data, straight from the sensor.  Level 1.5 data may have been processed to a specific gain setting (so that the sensor count to radiance level is known) as may have been geo-located so that the pixels appear as if from a perfect sensor (in the case of geostationary satellites).  Level 1B, 1C, 1D and 2 are also terms you may meet.
- left-hand circular polarised, type of radio-frequency signal transmitted for backup HRPT transmissions.
LNB - Low Noise Block.  The chunk you will see at the focus of your satellite TV dish, which comprises blocks to convert the Ku-band signal down to a more suitable frequency for cable transmission to your PC.  Typically there will be an RF-amplifier, mixer, and dual-frequency local oscillator - the front-end of a superhet receiver.  As the satellite transmissions include both vertically and horizontally polarised signals, the LNB will include polarisation switching capabilities.
- Loss of Signal, when a pass ends.
- Low Rate Information transmission - digital transmission standard for geostationary weather satellites when the data rate does not exceed 128Kbit/s.  There is an LRIT data channel on the EUMETCast service.



Meteosat - Meteosat 5, 6, and 7 are the current geostationary satellites operated by EUMETSAT.  Met-5 is over the Indian Ocean from 63E, Met-6 provides rapid scanning of Europe from 10E, and Met-7 provides coverage of Europe and Africa from 0.
Metop -
Metop is a series of three satellites to be launched sequentially over 14 years, starting in 2006, and forms the space segment of EUMETSAT's Polar System (EPS).
- a higher resolution sensor than the AVHRR, currently carried on the AQUA and TERRA satellites.  More information.
MSG Animator, MSG Data Manager
- my software for handling MSG data.
- Meteosat Second Generation.  The first generation includes the still-operational Meteosat-5, 6 and 7 satellites.  The MSG design has more channels and higher resolution.  There is a Meteosat Third Generation (MTG) satellite series at the very advanced planning stage.  Meteosat-8 (formerly MSG-1), the first satellite in the series, is now operational and will replace Meteosat-7.  MSG-2 was launched in 2005 and will likely be called Meteosat-9 when operational.
MTG - Meteosat Third Generation, the follow-on to MSG.
MTP - Meteosat Transition program - those EUMETSAT satellites required to provide coverage between the end of life of Meteosat-4 and the start of operation of the Meteosat Second Generation series.
MTSAT-1R - Japanese geostationary satellite covering Asia and Australasia.
- data packet intended for reception by multiple stations.  More information.



NASA - National Aeronautics and Space Administration (US).
NOAA - National Oceanic and Atmospheric Administration (US).
NTFS - New Technology File System.  Microsoft's advanced, more robust and more reliable file system which can be used with Windows NT, 2000 and XP.



PID - Packet Identifier - the label attached to different data streams in a DVB system.  Your PC can respond to one or more PIDs, allowing you to control what data you receive from all the data which may be available.
- Polar Operational Environmental Satellite.  The US managed polar orbiting satellite program.
Polar orbiter
- satellite in a polar orbit, typically successive satellite passes are 100 minutes apart, and pass progressively further west.  Your location will get one northbound (or Ascending) and one southbound (or Descending) pass per day.



QFH/QHA - Quadrifilar Helix Antenna - antenna with twisted elements for VHF APT reception.  Here is an example.



RHCP - right-hand circular polarised, type of radio-frequency signal transmitted for HRPT transmissions.
- Rapid Scanning Service.  EUMETSAT are using the Meteosat-6 satellite to provide images every 10 minutes over Europe.  Data is transmitted via the EUMETCast service.
RX - Receiver



SAA - Satellite Active Archive - library of NOAA data now replaced by CLASS.
- Satellite Application Facility.  A EUMETSAT group of experts who define the algorithms to produce derived products from satellite data.  SAF may also refer to the software used to run the algorithms.  An operational example is the Sea-Ice SAF who produce data from the polar orbiting satellites, and whose data is transmitted as part of the EUMETCast data stream. 
SatSignal - my APT decoding program.
SEVIRI - Spinning Enhanced Visible and Infra-Red Imager - the scanner used in the MSG satellites to convert visible and infra-red radiances into electrical signals.  Full description.
Single-chord operations - with GOES satellites, a way of maintaining location accuracy even when the moon or sun enters the earth location sensor's field of view.  More.
Spectral channel - that range of the electromagnetic spectrum to which a particular channel is sensitive.  A given satellite will have sensors covering multiple spectral channels.  For example, the earth emits its natural radiation with a maximum energy around the 10m wavelength, so to measure the earth's temperature one would use the 10m channel.  The sun emits most of its energy in the 0.4m to 0.7m region, so to measure things like surface reflectivity, spectral channels in the 0.6m region might be used.  The 12 channels on Meteosat-8.
SSP - Satellite sub-point.  That point on the earth's surface which is directly below the satellite.



TIROS - Television Infra Red Observation Satellite
- a device for re-broadcasting from a satellite, data which has been sent up from a ground station.  A transponder may be as simple as a receiver shifting the received signal to a different frequency followed by a power-amplifier.  A typical broadcasting satellite will carry many transponders, with some spares to allow for in-orbit failure.



VPN - Virtual Private Network.  For accessing your work network from home, a VPN is likely to prevent any of the network connectivity required by either a EUMETCast receiver or EUMETCast Data Management PC.



WEFAX - Weather FAX - analogue transmission standard used on geostationary weather satellites.  Will be progressively replaced with LRIT.
WMO - World Meteorological Organisation
WX - weather
WXtrack - my satellite orbit prediction and tracking program.

Is there a term you think should be here, or one I've got wrong?  Please let me know.

Copyright © David Taylor, Edinburgh   Last modified: 2015 Jan 18 at 09:32