Ok, so mangroves are important – now what? Well, now we must ensure that they are healthy, and we do so by conducting regular field surveys.
Field surveys are a good way of getting very detailed information from the mangroves. They allow us to see and measure mangrove growth, identify species, record animal sightings and much more.
However, field surveys can only cover a small portion of the ecosystem. They are time consuming and require a lot of human effort. After all, one has to navigate through the branched roots, the sticky mud and the bugs to get to the study site! Also, researchers and volunteers need to deal with high humidity and temperature, lots of mozzies and crocs. Mozzies can be worse than crocs! We all agree that field surveys are useful but, if we want to monitor larger areas, we have to use other tools. Namely, satellites.
Satellites have been taking pictures of earth’s surface for more than 30 years. Imagine that you kept all your medical records for the last 30 years and one day you decided to see how tall you were each year. With your medical records you can do that, and we can do the same with satellite imagery. But satellite images can tell us much more than this: we can see if mangroves expand or contract, grow or die, if they have been burned or bashed by storms, or if they have been chopped down for housing.
Satellites pass over Australia on a daily, weekly or fortnightly basis. For my research, I will use the images provided by the Landsat satellites because they have images of the mangroves around Cairns and Darwin dating back to 1987.
The good thing about these satellites is that they capture the images in the visible and invisible regions on the electromagnetic spectrum. In short, this means that satellites ‘see’ the mangroves not only as green (the leaves) or brown (trunk), but they can see in the infra-red region as well.
Plants, in general, are better seen in the infra-red light because they reflect so much infra-red light that they seem to ‘glow’. The healthier the vegetation, the more it glows. This is how we can tell if mangroves are healthy or if they are suffering from drought or disease.
In my research, I will use the infra-red light reflected from mangroves on over 900 images from Cairns and Darwin to assess the health of mangrove forests over the past 30 years. Because mangroves are so important to our communities, it is vital that we identify where sick mangroves are and why. By protecting the mangroves, we protect our communities from natural disasters and ensure a better and healthier environment for future generations.
Below are images from the Aceh region in Indonesia (Indonesia (4° 40.061' N; 95° 33.861' E). The left image dates 5 January 2003, about one year before the tragic boxing-day tsunami. The image on the right is from 18 December 2013, almost ten years after the tsunami. Satellite images make it easy to see the extent of the damage and how fast (or, in this case, slow) the recovery of mangrove ecosystems are after a catastrophic event.
“By protecting the mangroves, we protect our communities from natural disasters and ensure a better and healthier environment for future generations.”
Nicolás Younes, JCU PhD Candidate