Sandwich products

When studying various features (such as overshooting tops) across several bands or image products, it is sometimes difficult to properly compare these, looking at the images one-by-one, or side-by-side. For this reason a new type of products was introduced a couple of years ago, which is becoming more and more popular among forecasters, mainly due to its ease of use. The principle of the product is that two images are overlaid, the bottom one being (high resolution) visible band, and the upper one being any image or product we wish to compare with the visible band. In the next step, these two layers are "blended" together, using one of the advanced blending functions available in various graphic editors or graphic software packages. The resulting image shows the properties of both input images in a single one. Due to the way these images are created, these products became known as "sandwich" products (or alternatively "blended multi-layer images"). The most popular one is a combination of visible band with color-enhanced thermal IR band - in case of SEVIRI images a combination of HRV and color-enhanced IR10.8-BT image; an example is shown below in the Figure 15d. 

Figure 15d. The same storm as above, shown as "sandwich" product of HRV band and color-enhanced IR10.8-BT (190K-230K) image. The human eye can interpret the information carried independently in the source images more easily in this type of product, rather than comparing the source images side-by-side.

The sandwich product of visible and colour-enhanced thermal IR image was the first sandwich type of products. Based on good experience with this sandwich product, researchers started experimenting with other possible combinations (using different upper-layer images or products), and the one which seems to be also very useful is a combination of visible band with the "Storm RGB" product. An example of this type of sandwich product is shown on the next image, Figure 15e (below).

Figure 15d. The same storm as above, shown as "sandwich" product of the HRV band and the "Storm RGB" product. 

The additional benefit of the sandwich products is that they can show in loops the evolution of the storms, using (animation) one single product instead of switching between two (or more) of these, makes monitoring storm-tops (or convective storms in general) much easier. For further information about the sandwich products see e.g. this material, and examples (presentation and movie files) available here. Though, these sandwich products are relatively new, so it is rather unlikely that you will find these incorporated into your satellite data processing / visualization systems, but you may find these more and more often in various "case studies" or training material. This is the main reason why we decided to add this basic information about these products here, so that you are aware of these.