II. Dust Detection and Forecasting

Dust Detection by Satellite » Visible and IR images » Forward Scattering at Low Sun Angles

Dust Detection by Satellite » Visible and IR images » Forward Scattering at Low Sun Angles

The rules for visible imagery differ just before sunset and just after sunrise. If the satellite is looking in the general direction of the sun and the dust, the forward scattering of dust particles heightens the reflection from dust.

2-panel depiction of how the dmsp satellite over the equator views dust better in the early morning than early evening

Let's look at some examples. This MSG natural colour product, derived from visible and other solar wavelengths, was taken over the Arabian Peninsula at dawn on 20 Feb 2008. The forward scattering off a large dust cloud reveals an advancing dust plume. This cloud would be difficult to detect during the middle of the day in the same product.

MSG natural color image for 20 Feb 2008 with the forward scattering off a large dust cloud revealing an advancing dust plume

This MSG High Resolution Visible (HRV) image was taken in the early morning. The dust plume north of Africa is clearly evident due to the effect of forward scattering.

MSG HRV image showing a dust storm north of Africa in the early morning of 28 July 2005

Six hours later, at midday, the forward scattering effect is gone and the dust is much harder to see. It's only faintly visible against the dark water background.

MSG HRV image showing a dust storm north of Africa at midday on 28 July 2005