Why is quantum leap so underestimated

Measurement technology: technological quantum leap

Both parameters - soil moisture and salinity - have so far never been recorded globally from space due to their high temporal and spatial variability. That should change with the new technology used for the first time at SMOS.

The starting point was the realization that there is a direct relationship between the soil moisture and the salt content of the oceans on the one hand and the electromagnetic waves emitted by the earth in the microwave range around 1.4 GHz. Now it was time to implement this discovery in a new type of measuring device. It quickly became clear that an imaging microwave antenna with a correspondingly high spatial resolution would have a diameter of well over 15 meters for this frequency range.
This was unacceptable for an inexpensive Earth Explorer mission. In order to still be able to observe the earth's surface in detail, the clever space engineers from EADS-CASA Espacio resorted to a synthetic aperture, a kind of "virtual antenna" that is generated by the interaction of many small antenna receivers.

The result is the MIRAS (Microwave Imaging Radiometer using Aperture Synthesis). It consists of a central structure with three fold-out antenna arms, each four meters in length, arranged in a ypsilon pattern. Above are two solar panels, each four meters long.
A total of 69 LICEF antenna receivers are housed on the three antenna arms and on the outer surface of the central structure that is facing towards the ground. The abbreviation stands for Light Cost Effective Frontend. Each of the 69 receiving units measures the microwave radiation coming from the earth's surface in the L-band range from 1400 to 1427 MHz.

As SMOS moves along its orbit, an area about 1,000 kilometers in diameter is viewed from different angles below it. MIRAS can work in two measurement modes that allow the measurement of horizontal and vertical microwave components. Strictly speaking, the phase difference of the incident electromagnetic waves is measured on two or more LICEF antenna receivers whose distance from one another is known. From the phase difference one can then determine the origin of the wave and thus obtain information about the earthly measurement object.
The method is also called satellite-based interferometry. For the geosciences, MIRAS and the measurement methodology it uses represent a technological quantum leap.

The radiation emitted by the earth's surface and received by SMOS is not just a function of soil moisture and salinity. In order to be sure that the data provided by SMOS are correctly converted into soil moisture and salinity units, a number of effects that influence the signal must be carefully considered and eliminated. Therefore, the complex six-month commissioning phase is necessary (see article: "SMOS: Europe's newest environmental satellite").

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