European Space Agency (ESA) published an amazing photo of the Namib Desert from space, taken by the Copernicus Sentinel-2 Earth Observation mission on October 27, 2019.

Namib Desert from space
Namib Desert from space. Photo by the European Space Agency (ESA) CC BY-SA 3.0 IGO

Namib Desert from space

At 55 million years old, It is a coastal desert in southern Africa. The name Namib is of Khoekhoegowab origin (the most widespread of the non-Bantu languages of Southern Africa that contain “click” sounds) and means “vast place”.

In the Sentinel-2 image above, captured on 27 October 2019, a large portion of the Namib-Naukluft National Park is visible.

The park covers an area of almost 50,000 sq km (19,305 sq mi) and encompasses part of the Namib Desert and the Naukluft Mountains to the east. Straight, white lines visible in the right of the image are roads that connect the Namib-Naukluft National Park with other parts of Namibia.

The park’s main attraction is Sossusvlei – a large salt and clay pan visible in the center of the image. The bright white floors of the pan contrast with the rust-red dunes that surround it. Several dunes exceed 300 meters (980 feet) in height in the Sossusvlei area (some of the highest in the world). The complexity and regularity of dune patterns in its dune sea have attracted the attention of geologists for decades, but it remains poorly understood.

The dunes here are formed by the transportation of materials from thousands of kilometers away, carried by river, ocean current, and wind.

The Namib Desert stretches for more than 2,000 kilometers (1,200 mi) along the Atlantic coasts of Angola, Namibia, and South Africa, extending southward from the Carunjamba River in Angola, through Namibia, and to the Olifants River in Western Cape, South Africa.

The Namib is almost completely uninhabited by humans except for several small settlements and indigenous pastoral groups.

Sentinel-2 Earth Observation Mission

Sentinel-2 model
Model of a Sentinel 2 satellite. By Rama, CC BY-SA 2.0 fr, Link

Copernicus Sentinel-2 is a two-satellite mission to supply the coverage and data delivery needed for Europe’s Copernicus programme. The twin satellites are named Sentinel-2A and Sentinel-2B.

The launch of the first satellite, Sentinel-2A, occurred on 23 June 2015. Sentinel-2B was launched on 7 March 2017.

Sentinel-2 Earth Observation Mission systematically acquires optical imagery at high spatial resolution (10 m to 60 m) over land and coastal waters.

The orbit of the twin satellites Sun-synchronous (see notes 1) at 786 km (488 mi) altitude, 14.3 revolutions per day, with a 10:30 a.m. descending node. This local time was selected as a compromise between minimizing cloud cover and ensuring suitable Sun illumination.

The Sentinel-2 mission has the following key characteristics:

  • Multi-spectral data with 13 bands in the visible, near-infrared, and short wave infrared part of the spectrum
  • Systematic global coverage of land surfaces from 56° S to 84° N, coastal waters, and all of the Mediterranean Sea
  • Revisiting every 5 days under the same viewing angles. At high latitudes, Sentinel-2 swath overlap and some regions will be observed twice or more every 5 days, but with different viewing angles.
  • The spatial resolution of 10 m, 20 m, and 60 m (33, 66, 99 feet)
  • 290 km (180 mi) field of view
  • Free and open data policy

Notes

1. Sun-synchronous orbit

A Sun-synchronous orbit (SSO, also called a heliosynchronous orbit) is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet’s surface at the same local mean solar time (see the image below).

A Sun-synchronous orbit can place a satellite in constant sunlight, which allows the solar panels to work continuously. This orbit is also useful for imaging, spy, and weather satellites because every time that the satellite is overhead, the surface illumination angle on the planet underneath it will be nearly the same.

Sidereal day
The stellar day or “sidereal day” is shorter than the solar day. At time 1, the Sun and a certain distant star are both overheads. t time 2, the planet has rotated 360° and the distant star is overhead again but the Sun is not (from 1 to 2 = one stellar day). It is not until a little later, at time 3, that the Sun is overhead again (from 1 to 3 = one solar day). Image: Wikipedia

Sources

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