How cold does it get on earth? Remote sensing answers to a cool question

Just at the beginning of the cold season – at least those of you who are also living in the northern mid latitudes – following information is coming from NASA’s Goddard Center telling us the absolute coldest place on earth. Is the lowest ever captured temperature going to be located at a high ridge in the Antarctica, in a remote place in Greenland or on the top of Mount McKinley, the highest peak of North America located in Alaska holding the sobriquet of ‘coldest mountain’ in the world?

This question may be answered by the sensors of a couple of satellites that have been regularly recording surface temperatures since more than 30 years. Until date, the lowest ever measured temperature at a permanently inhibited place occurred in northeastern Siberia in the towns of Verkhoyansk and Oimekon in 1892 and 1933 respectively, when the air temperature dropped to bone-chilling 67.8°C below zero. The Russian Research Station Vostok in East Antarctic marks -89.2°C as coldest measurement.

In search of the coolest place on Earth, scientists analysed land surface temperature products from different satellites of 32 years. Moderate Resolution Imaging Spectroradiometer (MODIS) aboard of NASA’s Terra and Aqua satellites as well as the Advanced Very High Resolution Radiometer (AVHRR) on several satellites of NASA are capable to record thermal radiation from Earth’s surface also in places lacking much heat. The analysis revealed that a valley-like area along a 1000km stretch between the two summits of the East Antarctic Plateau, Dome Argus and Dome Fuji, exhibits temperatures plummeting to record lows dozens of times. Against the suspicion that ridges are likely to be the coldest spots, the lowest temperature accumulates in less elevated areas, pockets, in between. The new record of -93.2°C was set on August 10, 2010.

With remote-sensing satellites, scientists have found the coldest places on Earth, just off a ridge in the East Antarctic Plateau. The coldest of the cold temperatures dropped to minus 135.8 F (minus 93.2 C) -- several degrees colder than the previous record. Image Credit:  Ted Scambos, National Snow and Ice Data Center

The coldest places on Earth investigated by remote sensing means was located just off a ridge in the East Antarctic Plateau. The coldest of the cold temperatures dropped to minus minus 93.2 C — several degrees colder than the previous record. Image Credit: Ted Scambos, National Snow and Ice Data Center

 WHY ARE VALLEY SHAPED AREAS IN EAST ANTARCTIC COLDER THAN ELEVATION AREAS?

Low temperatures are fostered by clear sky conditions, when the ground radiates the heat into space and at the same time chills. If a clear sky persists the temperature around the snowy and icy surface becomes super-cold creating a dense layer of air that slides down the shallow slopes of East Antarctic domes, in order to accumulate in pocket areas and producing record low temperatures. The described effect is noticeable in all mountainous regions, where chilling air around the peaks floats downwards and is trapped in basin areas creating layers of cooler temperature. As a dweller from an Alpine country I know this effect very well.

With the higher resolution of the Thermal Infrared Sensor (TIRS) aboard LANDSAT 8, the scientists were able to pinpoint record-setting locations. The study is an example of showing the usefulness of Landsat 8 and the TIRS instrument. In my article on December 4, 2013, I reported about Antartic’s first high-resolution map relying on LANDSAT satellite imagery.  Landsat 8 has captured approximately 550 scenes per day of Earth’s land surface. USGS (US Geological Survey) processes, archives and distributes the images free of charge over the Internet.

Source: NASA Goddard Center, News

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First 3D topography of Great Barrier Reef derived from EO data

The first high resolution bathymetry of the Barrier Reef reveals a complete overview of the entire ecosystem as well as the sub aqueous topography of the single reefs at a horizontal resolution of 30m. Source: EOMAP

The first high resolution bathymetry of the Great Barrier Reef reveals a complete overview of the entire ecosystem and at the same time the subaqueous topography of the single reefs at a horizontal resolution of 30m. Source: EOMAP

I was recently invited to a Germany-based company that is specialized in aquatic remote sensing and just announced the finalisation of a large scale ocean mapping project, unique of its kind. I am talking about the launch of a set of high resolution maps showing the sub aqueous topography of the entire Great Barrier Reef. The collection constitutes the first digital dataset of the world’s vastest coral reef using satellite derived depth (bathymetry). Bathymetry refers to the remotely mapping of water depth using satellite information and is practicable down to a certain water depth, mostly shallow waters of 10 – 12m depending on the clearness of the ocean.

The world's largest coral reef extends over 2000km along the East coast of Australia.

The world’s largest coral reef extends over 2000km along the East coast of Australia.

Till day the ecologically sls is costly and also navigationally dangerous due to the shallow nature of the reef lagoons. In order to overcome such problems EOMAP Company decided to use satellite imagery and developed algorithms to retrieve water depth. In November this yearignificant coral banks of Great Barrier Reef have been surveyed on a digital basis to only less than a half of their extent. Mapping water depth by means of vesse the mapping of the Barrier Reef World Heritage covering an area of around 350.000km² at a spatial resolution of 30m was finalised. The default product relies on LANDSAT 7 satellite data, higher resolution maps applying WorldView2 satellite data with a 2m horizontal resolution can be delivered on request and a downscaled version of 500m (MODIS) is available for free. The vertical bathymetry accuracy is 10cm up to a depth of 12m when accuracy begins to diminish greatly. The dataset provides both a detailed view on the single reefs but also a complete perception of the entire coral ecosystem, according to the Australian project partners at James Cook University the largest mission of its kind in Australia.

Besides exploring water depth and sea floor EOMAP also keeps know how in assessing water quality parameters such as turbidity, total suspended matter, content of chlorophyll and yellow substances (suspended organic matter). The idea of Dr. Heege, CEO of EOMAP, is to regularly create and offer an updated version of the respective products for Europe. Other regions are scanned on request. The maps will be highly beneficial for monitoring water quality and estimate its responses to man-made and natural impacts such as cyclones, climate change, sea level rise and sediment transportation.

 What’s the difference to land surface classification?

Earth observation satellites measure the characteristics of light or radiance coming from an object of interest. All influences in between the earth’s surface and the satellite affect the energy that is recorded by the sensor requiring radiometric corrections. While land classification based on satellite imagery involves the correction of atmospheric influences, water depth assessment additionally implies the correction of sun effects on the water’s surface (sun glitter, angle, adjacency along the coasts) and the consideration of the water column itself (phytoplankton, sediments, suspended matter). For a final interpretation the applied algorithms distinguish between four types of seabed that entail a different colour (sand, rock/debris, vegetation and mixed seafloor (mainly vegetation). After that, the calculated radiance of the pure water column can be referred to a certain water depth.

Usefulness and purpose

Particularly the introduction of the coastal blue band beginning at 400nm has made satellite derived bathymetry (SDB) a robust technology since some water properties are discriminable within this spectral range. SDB allows to rapidly surveying remote, extensive or inaccessible areas at 5 – 10 times reduced costs compared to the traditional shipping methods. Particularly in shallow areas that are typical for all coral reefs the accessibility for vessels is challenging or even dangerous. The bathymetry and water quality maps as presented by EOMAP are very useful for obtaining an overview of a desired area and for deciding where more accurate data, for instance in-situ data is required. This information is essential for environmental monitoring, coastal engineering or reef management. The planned automatisation of the calculation process allows a repetition at a certain time interval producing a time series that is going to enable long-term observations. However, due to the limited accuracy the mentioned maps are not recommended for applications requiring nautical grade precision.

The algorithms to retrieve water depth and quality are also applicable to sweet water bodies as lakes or rivers. In this regard, a huge advantage lies in the standardized method of multi-sensor monitoring that produces a reliable, repeatable and harmonized product for a potentially large area. If we think of Germany for instance, every federal region uses different methods to measure and monitor water quality. Thus, the results are not consistent among themselves. On a national (large scale) level, a standardized product therefore represents the huge advantage of comparability.

Very high resolution bathymetry maps from the Great Barrier Reef as well as other location in the world are produced on demand. Source: EOMAP

Very high resolution bathymetry maps from the Great Barrier Reef as well as other location in the world are produced on demand. Source: EOMAP

Water quality maps demonstrating the chlorophyll content (upper left panel), turbidity (upper right) and two types of sea bed classifications at the bottom from different waters (sweet water and ocean). Source: EOMAP

Water quality maps demonstrating the chlorophyll content (upper left panel), turbidity (upper right) and two different sea bed classifications in the bottom row from different waters (sweet water and ocean). Source: EOMAP

With the idea of “Operational Satellite-Derived Bathymetry Service – Rapid, spatial, validated” EOMAP was awarded the Copernicus Master for cloud computing challenge in November 2013.

Source: EOMAP

 

 

 

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