The view from above

(Image: a plankton bloom across Ireland captured by Envisat. Courtesy of ESA).

What would a macroscope be? The opposite of a microscope, a device used to study nature at relatively small scales. A macroscope would be a tool to study things at large scales. If we focus on imaging, topics such as astronomy or remote sensing come to mind. But we can more generally think of a macroscope as a conceptual device to study large-scale phenomena.

It is probably fair to say that a virus has not clue that the cells it attacks are actually part of a very large and complex organism (sneeze). Have you ever tried to guess what an object is from an extreme close-up picture? It is really hard. Similarly, we are naturally limited to the experience of things in our planet at our local scales. Using our eyes, we can see objects from about a tenth of a millimeter to a few tens of km. The Earth is much bigger, and access to the global picture has had to wait until de advent of space exploration and the development of satellites.

Earth Observation satellites operate at heights that vary from a few hundred to a few thousand km, carrying instruments for remote sensing. High resolution optical cameras are one example, which can take astounding images from space with huge fields of view and resolutions below a meter. Take a look at Google Earth if you want to see optical images from space (and air). There are other optical instruments that provide information at lower resolutions—a few hundred meters—but at many frequencies. The human eye can detect electromagnetic radiation at 3 frequencies (red, green, blue). Some snakes can see in the infrared, bees in the ultraviolet. Each “color” gives us different information about the imaged object. The MERIS instrument on board the European satellite ENVISAT can “see” in 15 frequencies. With such multi-frequency instruments in space we can map and study vegetation at large scales, and also monitor biological activity in the oceans—such as algal blooms.

Algal blooms are explosions of small phytoplanckton algae due to the combination of high temperatures and upwelling—the rising of nutrient rich water from the ocean floor to the sunlit surface. These are photosynthetic organisms (also called the “grass of the sea”) that feed on natural or artificial nutrients and light. Blooms can easily be seen from space, with scales of up to several hundred km. Both their constituents (plankton) and their large-scale signatures escape human senses but can be seen using technology. By the way, some of these algae are very toxic to mammals—including humans—and are a threat to fisheries and aquaculture. Algal blooms can poison fish and marine mammals and remove oxygen from the ocean, causing marine life to suffocate. Such ocean color instruments provide early warning of increasingly frequent algae bloom occurrences.

Other remote sensing satellites are making fundamental contributions to science in fields of critical importance to our future. Examples include the study of ocean circulation, global rise of sea surface temperatures, the melting of glaciers and breakdown of ice sheets (yes, climate is changing), ozone and atmospheric pollution. These are a few examples of what we can see today with our “eyes in the sky”. They are helping us understanding how our planet works and the extent of human impact.