The Earth: SMOS satellite measurements improve as ground radars switch off

Hi My Friends: A VUELO DE UN QUINDE EL BLOG., Over a dozen radio signals that have hindered data collection on ESA’s SMOS water mission have been switched off. The effort also benefits satellites such as NASA’s Aquarius mission, which measures ocean salinity at the same frequency.

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The two images show monthly averaged sea surface salinity at northern latitudes as measured by SMOS. In May 2011, radio frequency interference (RFI) still hindered salinity readings. Over a dozen RFIs were switched off prior to May 2012, making salinity measurements more accurate thereafter. Credits: N. Reul, IFREMER/CATDS

 Over a dozen radio signals that have hindered data collection on ESA’s SMOS water mission have been switched off. The effort also benefits satellites such as NASA’s Aquarius mission, which measures ocean salinity at the same frequency.

We all know what happens when you place a cell phone too close to a speaker: seconds before the phone rings, that obnoxious buzz interrupts your favourite song.

This is radio interference – an unwanted reception of radio signals. Not only can it interrupt the music from your stereo, it can also impede satellite measurements.

ESA’s Soil Moisture and Ocean Salinity (SMOS) satellite was launched in 2009 to improve our understanding of our planet’s water cycle. In order to do this, it measures the microwaves emitted by Earth in the 1400–1427 MHz range. 

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The two images show radio frequency interference (RFI) at northern latitudes in February 2011 and February 2012. Several radars are observed (the red ‘dots’, visible because they exceed the natural variability for brightness temperature measurements over land) over Northern Canada and at the southern tip of Greenland. The authorities from Canada and Greenland were informed, and requested to take actions. Canada started to refurbish their equipment in autumn 2011, while Greenland switched off their transmitters in March 2011. At least 13 RFIs have been switched off in the northern latitudes. However, the few remaining RFIs can contaminate areas 3000 km away from the original source, especially in passes ascending towards North America. Credits: ESA

 Over a dozen radio signals that have hindered data collection on ESA’s SMOS water mission have been switched off. The effort also benefits satellites such as NASA’s Aquarius mission, which measures ocean salinity at the same frequency.

We all know what happens when you place a cell phone too close to a speaker: seconds before the phone rings, that obnoxious buzz interrupts your favourite song.

This is radio interference – an unwanted reception of radio signals. Not only can it interrupt the music from your stereo, it can also impede satellite measurements.

ESA’s Soil Moisture and Ocean Salinity (SMOS) satellite was launched in 2009 to improve our understanding of our planet’s water cycle. In order to do this, it measures the microwaves emitted by Earth in the 1400–1427 MHz range. 

Download:

HI-RES JPEG (Size: 3675 kb)

The Soil Moisture and Ocean Salinity (SMOS) mission makes global observations of soil moisture over Earth’s landmasses and salinity over the oceans. Variations in soil moisture and ocean salinity are a consequence of the continuous exchange of water between the oceans, the atmosphere and the land – Earth’s water cycle. Credits: ESA/AOES Medialab

 At least 13 sources of interference have now been switched off in the northern latitudes. This has significantly improved SMOS observations at these high latitudes, which were previously so contaminated that accurate salinity measurements were not possible above 45 degrees latitude as the satellite headed north.

However, the few remaining sources can contaminate areas 3000 km away, especially as SMOS climbs north towards North America.

The efforts to reduce interference will benefit other missions carrying similar detectors, such as NASA’s Aquarius satellite, which was launched last year.

Aquarius also observes ocean salinity and, in addition, it measures sea-surface roughness to help understand how roughness affects salinity measurements.

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The two images show monthly averaged brightness temperatures, which corresponds to microwave radiation from Earth’s surface, at northern latitudes for May 2011 and May 2012. In May 2011, before 13 sources of radio frequency interference (RFI) in Canada and Greenland were either refurbished or switched off, a circle of higher brightness temperatures can be seen, exceeding the expectations for natural variations of such measurements in the northern latitudes over ocean. Once the RFI sources were switched off (prior to May 2012), natural variability returns. Higher brightness temperature measurements, being the starting point for salinity retrievals, lead to erroneously fresher water in the oceans.

Credits: N. Reul, IFREMER/CATDS

A unique feature of SMOS is that it also measures soil moisture. SMOS and Aquarius readings are highly complementary: SMOS repeats coverage faster and at finer detail, while Aquarius has better ‘pixel by pixel’ accuracy.

Scientists are trying to combine both sets of measurements in the best way to improve global salinity maps.

“Combining SMOS and Aquarius new observations will allow us to map ocean surface salinity with an unprecedented spatial and temporal resolution,” said Nicolas Reul from the French Research Institute for Exploration of the Sea.

“In particular, salinity fronts and the movement of water across tropical oceans and within strong currents – such as the Gulf Stream – shall be better detected and tracked than with single-sensor observations.”

ESA
 Guillermo Gonzalo Sánchez Achutegui
 ayabaca@gmail.com
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