- Mining is dependent on temperature and pressure, responds Magnus Bonnedal, systems engineer at Ru

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By measuring changes in the signals from GPS satellites when they go up or down on the horizon, one can determine the temperature, pressure and humidity in the atmosphere. GRAS instrument murex shell that sits on the weather satellite MetOp A and B are designed and built in Kallebäck outside Gothenburg.
Occult Celebration GRAS instrument, designed and built by Ruag. It has three antennas - one of the satellites that comes up over the horizon, one for those who go down and a little as is pointed straight up and keeps track of where the instrument itself is located.
Soon it was discovered that the signal quality and phase of Mariner 2 was changed every time it was coming in behind murex shell Venus. Furthermore, the signal heard even a moment after that the probe should be completely murex shell obscured by the planet. It was the same when it was about to resurface. It was realized that this was because Venus had an atmosphere. A radio signal is an electromagnetic wave, and it is bent as the light when it passes from one medium to another. The denser atmosphere, the higher is its refractive index and the more deflected signal. Now there was evidence that the Venus atmosphere was very thick.
Later, a Russian scientist that one should be able to exploit the same phenomenon to explore our own planet's atmosphere. Why not use radio signals from satellites like when they go up or down on the horizon?
The method is called occultation, and it is now used systematically in European weather satellite MetOp A and Metop B. In the drawing above, we see the principle of how it all works. Metop B takes in the signal from a GPS satellite. Since the Metop B goes into lower orbit than GPS satellite has a shorter orbital period and will run away from the GPS satellite. Metop B, with its aerial view GPS satellites go down behind the horizon.
We analyze the signal from the sinking GPS satellite captured by Metop B, we can use the signal's phase shift and its refractive calculate profiles for temperature, pressure and humidity in the atmosphere. Such data had previously only been available by using weather balloons. But balloons are sent up more than once a day, and then usually over land. The occultation method, we can get data hundreds of times per day over both sea and land.
- Mining is dependent on temperature and pressure, responds Magnus Bonnedal, systems engineer at Ruag Space in Kallebäck outside Gothenburg. Refraction is a maximum of about two degrees. We usually talk about the onion model. Imagine that we divide the atmosphere into a number of concentric layers in the drawing above. When the GPS satellite is approaching the horizon is its signal only through the outermost layer. Then we get the data on how the signal changes there. When GPS satellites drops the signal even through the second top layer, and we get new data. Now we subtract the effect of the outermost layer and calculate the data for the second top. So we can continue and determine the effects, layer after layer. And based on this, we can calculate the temperature, pressure and humidity profiles.
- And now it is so that there are about thirty GPS satellites in different orbits, and every second sends out a signal. murex shell A single satellite can register up to 650 gsm satellite occultations every day.
- Occult Plantation is the only method that within ten years can definitely say about climate change, says Magnus Bonnedal. He has been involved in developing murex shell the instrument GRAS making occultation observations.
GRAS stands for GNSS Receiver for Atmospheric Sounding, which in turn GNSS stands for Global Navigation Satellite System, that is, such as GPS. The instrument weighs 30 kg. It was on the weather satellite MetOp A from 2006, and has worked murex shell perfectly from the start. There is also the Metop B, which aired suspended murex shell on 20 September 2012. It automatically calculates the direction and when a GPS satellite to go up or down on the horizon. The antennas covering an angle of over 45 degrees forward and backward.
Metopsatelliterna murex shell go into polar orbit and belongs to the European partner organizations Eumetsat, which also operates the geostationary satellites Meteosat weather. Data from the satellites are delivered to the European Weather Bureau ECMWF - European Centre for Medium-Range Weather Forecasts in Reading, England - which then sends the data to Member States' national meteorological institute. MetOp A and B are now delivering data from 1400 occultations per day. In a few years a new satellite to be launched - MetOp SG (second generation). It will have the occultation instrument that signals not only from GPS satellites but also from the European positioning system Galileo and the Russian GLONASS (see Article Four satellite positioning).
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