Detroit: reducing the noise speckle

This Sentinel-1 radar image takes us to the major city in the US state of Michigan, known for its Motown sound, rock music, world class museums, automobile culture, sports teams, arts, and theatres: Detroit.

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Image obtained by mediating 21 Sentinel-1 Co-Pol product over Detroit
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Sentinel-1 Co-pol image over Detroit

The image was created by mediating 21 radar scans from Copernicus Sentinel-1 captured from January 2016 to February 2017 for reducing the noise speckle.

This noise is an undesired effect that degrades the quality of images, and mostly categorised as multiplicative noise; it causes difficulties during the process of interpretation and analysis of SAR images.
Speckle noise is generated during the process of creating the SAR image and it is caused by coherent radiation.
Within every pixel many objects contribute to backscattering. The result is the coherent sum of all contributions (vector addition of all these contributions in the complex plane).
As shows below every grey vector corresponds to a scatterer in the resolution cell. Resultant amplitude of the pixel (red and yellow vector) is the coherent sum of all those individual contributions .
Screen Shot 2017-05-26 at 08.15.13

Addition of backscatterrer from a collection of scatterers can produce random constructive (increase from the mean intensity-bright pixel, as the yellow resultant vector in figure) or destructive interference (decrease from the mean intensity-dark pixel, as the red resultant vector in figure). Speckle is an inherently exist salt-pepper noise that degrades the quality of the SAR images and makes interpretation of features more difficult.

By averaging more images, the speckle noise is mediated and further details of the city’s urban structure are exalted. In this way we see with more defined edges the chessboard structure of Detroit: as a matter of fact the entire American territory is measured and ordered by a continuous and iso-oriented grillage of 1-mile side as is decreted by an order promulgated by President Jefferson.

Moreover we can better see that Detroit is bordered to the south by the Detroit River, which divides the US and Canada: Detroit is the only place in the continental US where you have to go south to enter Canada.

With the Detroit River International Wildlife Refuge, Detroit contains the only international wildlife preserve in the North America, uniquely located in the heart of a major metropolitan area.

The Refuge includes islands, coastal wetlands, marshes, shoals, and waterfront lands along 48 miles (77 km) of the Detroit River and Western Lake Erie shoreline.

Below a particular of Downtown includes the bright radar reflections from many of the prominent skyscrapers. Downtown is adjacent to the riverfront, so the rest of the city expands north, east, and west from downtown. For major roads, the Detroit area is laid out in wheel-and-spoke configuration downtown, strip-farm configuration along the river front, and grid pattern elsewhere.

The wheel-and-spoke configuration was designed in the 18th century for tactical reasons when Detroit was a fort. Mile roads run east-west, start north of downtown Detroit and continuing through Macomb and Oakland counties.

Too bad that Sentinel1 cannot capture Detroit’s music: […] Detroit’s music is probably the best on the planet. After New Orleans, which is the tree’s roots, the trunk is Interstate 75, Arrives at Memphis, Detroit and Chicago, with ramifications extending to New York and Los Angeles. But the trunk, man, the trunk starts from New Orleans and comes straight to Detroit. All of these people have come here to find a better job, taking behind funk, soul, gospel, blues.So came the greatest musicians in the world, the best jazz players, the best bluesman, See the Motown, see rock’n roll, Stooges, MC5, Alice Cooper, Ted Nugent, Bob Seeger, Jack White, Derrick May … it is the sound of this beautiful endless culture … there is an energy in this city, which you do not find anywhere else. They spend their lives building cars, and when they go out they want to hear good music: it’s better that you sound good […] ” (‘City Blues’, Vittorio Buongiorno)

References:
https://www.ripublication.com/ijaer16/ijaerv11n15_61.pdf
https://saredu.dlr.de/
http://wikitravel.org/en/Detroit
City Blues –Vittorio Buongiorno

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