The location of the sunglint at different times is given in this diagram. These show as very bright patches appearing every night, but only meaningful in relation with the Meteosat-10 optics.Īround midnight in Greenwich, the glaring reflection (sunglint) quickly moves from west to east, a bit surprisingly. The Meteosat-10 Natural Colour RGB animated loop (Figure 37) shows the Sun reflecting on the Antarctic around 0:00 UTC on 15-21 December, from Meteosat-10, with bright flares south of 66°S where light slant touches the cold waters in between widespread cloud cover.

The stronger illumination in the north will not convert into higher atmospheric temperatures until several months later, due to cloud, air and ocean thermal inertia. The polar orbit reaches further north than Meteosat, and allows a glimpse into the almost clear Kara Sea and the area east of Svalbard.įigure 37: Meteosat-10 Natural Colour RGB, 15-21 December 00:00 UTC This image (Figure 25) uses VIIRS Day-Night Band (DNB) channel at 00:00 UTC on 21 June. The cloud-free areas in the Norwegian sea are pictured with a better resolution by the VIIRS instrument on SNPP, without sunglint. The sensors for solar radiation saturate for strong signals and can 'blind' neighbouring pixels to the west. The evolution of the sunglint area on water surfaces can be followed in the animation, progressing from west to east.

The grazing sunlight reaching the satellite is enhanced by reflection on flat surfaces, as lakes or calm ocean areas. The Meteosat-10 imagery, 20 June 22:00 UTC–21 June 01:45 UTC around midnight shows the Sun-illuminated region in the upper part, close to the Earth's upper boundary, as a result of maximum Earth tilting at this time of the year. In the Arctic region, above 66.6 degrees latitude, the Sun does not set in 24 hours. This solstice marks the shortest night in the Northern Hemisphere and the longest night in the Southern Hemisphere. Close to the solstice Sun slant reflection occurs in the forward direction on sea portions without waves, close to 70 degrees north latitude.Įxamples are provided on Figures 5-7, first for Himawari around 15:00 UTC on 20 June, then for Meteosat-11 around 00:00 UTC on 21 June, then for GOES-16 around 05:00 UTC.Ĭuriously, the glint moves eastwards inside each satellite field of view, but follows a westward satellite sequence - the satellite and the Sun being on opposite sides of the Earth.įigure 24: Meteosat-10 channel 10.8µm completed with the natural solar composite in the upper boundary, 20 June 22:42 UTC On the geostationary satellite images, the sunglint evolves along an oval during the course of the day (Figure 4). Oceans are also more reflective and brighter at shorter solar wavelengths, adding noise to a sunglint detection. Note that spectral channels around 800nm (0.8µm) were preferred for tracking the sunglint position over water bodies, instead of the 600nm region which shows less reflection for land, hence a worse land-sea contrast. A similar analysis (not shown) explains the reflection pattern in the White Sea, east of Scandinavia, for Meteosat-11 (Figure 6) According to Canadian ice products, the amount of ice on Baffin Bay that week was 90% below the 30-year average for areas D and C, as revealed by the strong sunglint at 05:10 UTC. Area A on Figure 3, with only 10% of ice, reflects moderately in both situations. Outside of that area, around 20 minutes after or before sunglint, the reflectivity pattern is the opposite, since ice is not flat and puts light into the satellite. In the sunglint area, waters with thick ice are not reflective, whereas ice-free waters are very reflective. Figure 3 offers a comparison of channel 0.8µm and the ice concentration product by the Government of Canada. Solstices can be applied to monitoring Arctic ice. For other satellites, one hour is due to be added for each 15° of sub-satellite point longitude

Figure 4: Centre of the sunglint location for the 21st of the month at any time (white squares) from the perspective of a geostationary satellite.

2020 solstice and equinox dates