Early morning sunglint over the Indian Ocean

by Ivan Smiljanic (DHMZ)

Unlike the usual daytime images from satellite visible channels, in the case of the sunglint, water surfaces appear brighter than clouds. In these cases visible images seem to have inverted grayscale. This can be well observed using two different time steps of the same visible channel, like in this case.

In this particular example the movement of the sunglint approximately along the line of ITCZ (area with dense convective activity) can be observed.

The High Resolution Visible (HRV) animation show this effect in the West Indian Ocean.

The imagery shows that the prevailing wind was easterly and the Reunion and Mauritius Islands are acting as a windbreak to the west. Therefore, the sunglint effect is more pronounced in the west of the islands as the sea is calm (especially for Reunion which has much higher mountains than Mauritius).

On the comparison between two different time steps inverse reflectance can be observed.

Normally water masses are good absorbers of visible radiation coming from the Sun, therefore, they appear dark in the visible satellite imagery and clouds appear very bright.

In cases of sunglint total reflection makes water surfaces very bright, so relative to them clouds appear as darker patches on the images. This is especially the case in the morning when absolute reflection from the clouds is also smaller.