The Science Of Fall Leaf Color Change And Detection From Space

Fall foliage within the Appalachian Mountains on October 17, 2025. The picture was captured by a climate satellite tv for pc.

NWS Atlanta

It’s that point of the yr. The leaves are beginning to change colours. This week the Nationwide Climate Service in Atlanta shared the satellite tv for pc picture above displaying fall foliage modifications within the Appalachian Mountains. Whereas nothing replaces seeing them up shut, what’s the science of how the leaf colour change is detected from area?

The satellite tv for pc picture reveals mild brown and rust colours rising. Nonetheless, drought within the area has additionally had an influence. The NWS Atlanta wrote, “Sadly, the drought has led to leaves drying up and falling off of timber earlier than their colours peak throughout components of north and central Georgia.” Earlier than stepping into foliage detection from area, let’s discover why leaves change colour presently of yr.

Why Do Leaves Change Shade?

NASA has a terrific web site that explains the method and factors out that tree colour modifications within the fall are associated to climate, day size, and tree variety. The Appalachian Mountains have a wide range of deciduous tree species native to the area. By the best way, the phrase “deciduous” means the shed the leaves yearly. NASA wrote, “The colour of fall foliage is determined by the tree species and the combination of pigments within the leaf.” These pigments are chlorophyll (greens), xanthophylls (yellows) anthocyanins (reds), and carotenoids (oranges). The web site went on to say, “In spring and summer season chlorophyll is the pigment that provides leaves their inexperienced colour. On the finish of summer season, the decreased daylight and cooler temperatures, trigger chlorophyll to interrupt down, which expose the carotenoid (yellow, orange, and brown) and anthocyanin (purple, purple, and crimson) pigments.”

As NWS Atlanta famous about drought circumstances in northern Georgia, climate performs an essential function within the course of. Drought circumstances have brought about important leaf fall. Nonetheless, heat sunny days and funky nights are the best recipe for probably the most vibrant colours. How does a satellite tv for pc instrument “see” the colours?”

How Does A Satellite tv for pc Instrument Detect The Shade Change?

The reply is determined by the instrument and intent. Within the picture beneath, derived merchandise referred to as vegetation indices are produced from the NASA Average Decision Imaging Spectroradiometer (MODIS). These pictures present Enhanced Vegetation Index for the summer season and fall of 2014. A majority of these indices have been developed by scientists to check the function of vegetation modifications to a bunch of Earth system science processes.

Let’s now circle again to the picture shared by the NWS. It was a real colour picture. NOAA’s web site explained, “GeoColor is a multispectral product composed of True Shade (utilizing a simulated inexperienced part) throughout daytime, and an Infrared product that makes use of bands 7 and 13 at evening.” What on this planet did all of that jargon imply?” Let’s evaluate the electromagnetic spectrum.

NASA defined the EM spectrum as, “The vary of all sorts of EM radiation. Radiation is power that travels and spreads out because it goes – the seen mild that comes from a lamp in your own home and the radio waves that come from a radio station are two sorts of electromagnetic radiation.” As you see from the graphic beneath, X-rays, gamma-rays, infrared mild, microwaves, and ultraviolet mild are there too. People use the seen mild portion of the EM spectrum to see.

Within the GeoColor picture on the high of this text, the instrument is sensing the leaf colour in the identical method that your eyes would should you have been using alongside on that satellite tv for pc. Nonetheless, different components of the spectrum can be utilized to measure issues too. For instance, I examine city climate and local weather course of. The picture beneath reveals warmth signatures of U.S. Midwest cities utilizing the infrared a part of the spectrum. When you have ever had your physique temperature measured with an infrared gun, it’s a related course of.

Take pleasure in these colours.