Eye in sky to track change
THERE is plenty of excitement these days generated by the many spectacular images of objects in our solar system and right out to distant galaxies, whose light left them billions of years ago.
However, it is important to remember that there is a planet of major importance that we need to observe in great detail — and we are standing on it. It is our Earth, the third from the sun in the array of our star’s planets.
To continue the study of our planet from space, an advanced satellite for Earth observation has recently been launched, and it is the ninth of a series. The US satellite Landsat 9 was sent into Earth orbit on September 27, and it promises to return information that will play a vital role in our quest to study climate change.
The Landsat series of Earth-observation satellites started with the first launch in 1972, which was given the name Landsat 1, after it was originally called Earth Resources Technology Satellite 1. All have been successful, except for Landsat 6, which failed to reach orbit because of an explosion in the rocket’s fuel system.
Observation of Earth from space is not as simple as taking up a digital camera.
The sophisticated equipment observes our planet in a range of wavelengths, some of which are not visible to the human eye.
A very important region of the spectrum for this purpose is the infra-red, which has wavelengths longer than can be detected by our eyes.
Imagine, for example, walking into a large, dark room in which 50 people were each aiming a TV remote control towards you.
You would, of course, see nothing, but if your eyes were sensitive to those longer wavelengths emitted by the remotes, you would see 50 bright points of infra-red light and be able to deduce the directions of everyone in the room.
Landsat 9 carries two instruments, called the Operational Land Imager 2 (OLI-2) and the Thermal Infra-red Sensor 2 (TIRS-2).
OLI-2 will capture visiblelight images, and images in two parts of the infra-red spectrum called the near infra-red and the short-wave infra-red, while TIRS-2 will be used at infra-red wavelengths to measure the temperature of Earth’s surface. These will work in tandem with similar instruments aboard the still-operational Landsat 8, which was launched in 2013.
Among its many roles, Landsat 8 has been used to image Tasmanian bushfires, including the Riveaux Road fire in January 2019, near Lake Pedder, which was started by a lightning strike.
The type of instrumentation used can show the thermal glow from the still-warm surface well after the fires have been extinguished or have moved on to other areas.
There are many other benefits of this type of observation. More can be learnt about land use, changes in our forests, and even the coastal concentration of chlorophyll, which is an indication of the presence of tiny organisms called phytoplankton — an important component of the marine food web.
Coverage of the whole surface of Earth is possible with satellites such as Landsat because they are in near-polar orbits, which take them almost above the North and South poles in each 99-minute passage around the planet. As they look down from about 700km up, they pass over each part of Earth about the same local time each day, so it is said that they are in a sun-synchronous orbit.
Such an orbit has the great advantage that it allows easy comparison between images taken on different days — perhaps months or even years apart — to see what changes may have taken place.
The Landsat series of satellites has been spectacularly successful, and I am confident that Landsat 9 will continue the observations brilliantly at a time when learning about changes to our planet is more important than ever before.