Sunglint during March equinox

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Satellite imagery during the Spring Equinox (Autumn in Southern Hemisphere) captured very obvious sunglint near the Equator.

Date & Time
20 March 2018 03:00 UTC
Meteosat-11, Terra
Natural Colour RGB, True Color RGB

By Ivan Smiljanic (SYSIS)

Equator was in the focus on 20 March because the Sun shone the brightest there on that day. The equinox happened at exactly at 16:15 UTC. After that time Sun starts to shed more energy on the northern hemisphere for the next six months.

Figure 1: Meteosat-11 Natural Colour RGB animation, 20 March 03:00–06:00 UTC

Peak reflection of the Sun in the equator area is best observed through a sunglint. The Meteosat-11 Natural Colour animated loop (Figure 1) shows peak reflection of the Sun in the morning hours from the water surfaces of Indian Ocean.

Figure 2
Figure 2: Terra MODIS True Color RGB, 20 March 05:15 UTC

Sunglint over Indian ocean was also observed with the MODIS instrument on the Terra satellite (Figure 2). The peak of the glint expands to the north (towards Sri Lanka) and towards the south as well.

Due to the advanced resolution of the MODIS visible channels (500 m) the contours and shape of the glint are more obvious than on the Meteosat satellite imagery (max. 1 km for the broadband HRV channel, 3 km for the animated Natural Colour RGB).

Roughness of the water surface leads to less Sun reflection back to the imaging instrument. This roughness is mostly affected by local winds.

Essentially the difference between MODIS and Meteosat-11 stems from their orbit. Sun-synchronous orbits see the sunglint as a vertical column, where the the max intensity is found at the latitude where the Sun is positioned at the back of the satellite, i.e. where the Sun falls vertically. From the GEO orbit the sunglint is almost circular, the position depending on the Sun-satellite geometry.

Related content

Sun straylight seen over Africa (green area marked by red arrow) on Meteosat-10 Fog RGB, 21 March 23:00 UTC

Previous case studies

March equinox 2017 (20 March 2017)
Sunglint during September equinox (22 Sept 2016)
Spring equinox 2016 (20 March 2016)

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