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February 18, 2019

Earth observation for weather prediction – solving the interference problem

By ITU News

“Today, several dozen satellites contribute to the accumulation of critical knowledge about the Earth’s system, enabling scientists to describe specific links between a major natural disturbance in the upper atmosphere, and changes in the weather thousands of miles away,” says Mario Maniewicz, Director of the ITU Radiocommunication Bureau. “As accurate weather predictions need to start from the best possible estimate of the current state of the atmosphere, it is crucial that meteorologists have real-time, accurate global observations about what is happening in the Earth’s atmosphere over land and oceans. And for this, they rely on space sensing.”

Space sensing relies on the deployment of sensors to obtain data critical for Earth observation from space. Active sensors are radar systems on spaceborne platforms. They obtain data through the transmission and reception of radiowaves. Passive sensors, meanwhile, are very sensitive receivers that measure the electromagnetic energy emitted and scattered by the Earth, and the chemical constituents in the Earth’s atmosphere. They require protection from radio-frequency interference.

Josef Aschbacher, Director of Earth Observation Programmes at the European Space Agency (ESA), explained in the latest ITU News Magazine edition how interference by other radio-frequency services may impact passive remote sensing, and consequently important Earth-observation applications that depend on these measurements.

Mr Aschbacher says that future generations must still be able to enjoy the social and economic benefits brought by remote sensing in meteorology, climatology, land and water management, agriculture, natural disaster prediction, and many other fields of public and private interest. For this to happen, he says that all administrations need to act wisely, with a long-term vision.

He stresses the importance of the appropriate provisions in the Radio Regulations (RR) to prevent harmful interference, and explains how passive spaceborne sensors use a limited number of radio-frequency bands identified in the RR on the basis of the nature of the emissions from land, atmosphere or ocean, spectrally located in a wide range from ~1 GHz to ~1 THz.

Spaceborne sensors measure the background natural radiative emission floor, therefore any man-made signal (e.g. communications, radars) that rises above this natural emission floor will likely interfere with the measurements. This interference can be tolerated only if its energy is well below the sensor sensitivity.

Given the extremely low levels of the natural emissions, even very low levels of radio-frequency interference (RFI) may degrade the passive sensor measurements.

The market needs are leading to an increasing number of commercial applications with their associated radio-frequency spectrum needs, covering not only the already congested ranges in the radio-frequency (RF) spectrum but also higher frequencies.

This situation is becoming a serious concern, says Aschbacher, to ensure protection of critical Earth observation applications.

According to Aschbacher, the only way to mitigate the problem of increase in radio-frequency interference to passive remote sensing, is to define appropriate and enforceable limits in the Radio Regulations and ITU–R Recommendations for active systems that may impact passive sensor measurements.

Read Aschbacher’s full article, and more, about the needs of the space science community, in the latest edition of the ITU News Magazine, and how decisions at the ITU World Radiocommunication Conference 2019 (WRC-19), to be held in Sharm El-Sheikh, Egypt (from 28 October to 22 November), can provide appropriate protection to space science.

ITU is now in full preparation mode for WRC-19, with the Second session of the Conference Preparatory Meeting (CPM19-2) in Geneva, Switzerland, taking place from 18-28 February 2019. The meeting will produce the CPM report, which will provide useful information to ITU Member States for their preparation of proposals to the WRC later this year.

“It is crucial that meteorologists have real-time, accurate global observations about what is happening in the Earth’s atmosphere.” — Mario Maniewicz

ITU’s WRC-19  will review, and, if necessary, revise the Radio Regulations, the international treaty governing the use of the radio-frequency spectrum and the geostationary-satellite and non-geostationary-satellite orbits.

The Conference will also address any radiocommunication matter of worldwide character, instruct the Radio Regulations Board and the ITU Radiocommunication Bureau, and review their activities, determine the ITU Radiocommunication Sector Questions for study by radiocommunication assemblies and the study groups in preparation for future radiocommunication conferences.

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Earth observation for weather prediction – solving the interference problem

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