Satellites

Dundee Satellite Receiving Station typically receives images from satellites which can be used for studying:

There are four main satellite series:

Satellite series Main use Orbit Comments
NOAA Cloud, land, ocean temperature Polar orbiting
MetOp Cloud, land, ocean temperature Polar orbiting
SeaStar Ocean colour Polar orbiting Also known as OrbView-2
Meteosat Whole earth Geostationary orbit Also GOES, GMS and IODC (was IndoEx) satellite series
EOS As NOAA plus SeaStar (see MODIS) Polar orbiting Terra (EOS-AM1) was launched on 18 December 1999

See our list of all polar-orbiting satellites from which we receive, where there is a table of satellites, scanners, satellite identifiers, launch dates, and so on.

Scanners

Each satellite carries multiple sensors but the ones we receive can detect visible and infra-red radiation. The scanner aboard the NOAA series is called AVHRR, that on SeaStar is called SeaWiFS and that on EOS is called MODIS. Meteosat carries VISSR and Meteosat Second Generation carries SEVIRI. Each scanner simultaneously detects several bands of radiation, for example the AVHRR scanner has two channels of visible data and three of infra-red. The scanners generally have a maximum resolution of 1km per pixel at the location directly beneath the satellite, although some MODIS channels are higher resolution (500m per pixel and 250m per pixel).

To see which parts of the electromagnetic spectrum are sensed by each scanner please see the comparison of all sensors document.

Raw data from the AVHRR and SeaWiFS scanners is transmitted in HRPT format which includes the output from all channels plus calibration, navigation and spacecraft state-of-health information. Meteosat is transmitted in PDUS format, EOS is transmitted in CCSDS format. Full details of formats are in our Satellite Data File Formats Document.

Calibration

The raw data from the scanners must be calibrated to take into account their non-linearities. We can provide calibration data for the NOAA and SeaStar satellites. After scanner calibration the data can then be calibrated to take into account the effects of the atmosphere and other interference. The result can indicate cloud, land or sea surface temperature.

Orbits

Apart from Meteosat, which is a geostationary satellites, all the satellites from which we receive are polar-orbiting. In order to predict their orbit, and thus know where to point our antennae, we use a set of orbital parameters for each satellite. From these we can produce predictions of future satellite passes. Customers who make arrangements with us can also produce custom predictions for anywhere in the world. For those interested there is an explanation of the orbital parameters.

Knowing the orbital parameters, we can calculate the area which will be covered by a particular pass of a satellite. Images of the area may be viewed from each quicklook page. from the predictions page or from the results of a pass database search.

Orbital parameters are distributed in many formats, such as TBUS bulletins, TLE (two line elements), or IIRV (improved inter-range vectors). For more details see CelesTrak.

Navigation

Given the orbital parameters and the exact time of each line of data received from the satellite we can calculate the earth location of each pixel in the image. Doppler corrections recorded by our antenna controllers adjust the time to make navigation more accurate, as the satellite's clock can drift slightly. The resulting times are stored in our pass database to ensure future calculations are as accurate as possible.

Some navigation errors are caused by spacecraft attitude and cannot be fixed by time adjustment alone. These errors can be found by analysing the image data to find coastlines and adjusting the assumed attitude until the coastlines fit known locations. Dundee developed Landmark software for this purpose; it can adjust the assumed time, yaw, roll and pitch of the spacecraft until the image coastline fits the true coastline. Landmark is now available from VCS.

If you have ordered HRPT data and wish to navigate it you can use our hrpttime program to extract the line times and our timeloc program to perform the navigation calculations. See our HRPT line geolocation page for details.

More information


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