Tips and Tricks for Error-free Classification!
Hi! My name is Tom Bell and I am a scientist with Floating Forests. For the past 3 years, I have been working with Landsat images to estimate giant kelp biomass along the California and Baja California coasts. I have also had the opportunity to advise over 20 undergraduate analysts at the University of California, Santa Barbara to help process these images.
One of the great things about Floating Forests is that image processing has been simplified so that users need very little training before they are off and running. However, this does not mean that every image will present a straightforward classification. Today, I want to take you through some common kelp classification errors and give you some tips on how to determine if that the questionable blob is kelp.
First lets start with the natural history of giant kelp and the general characteristics of the environment where it exists. Giant kelp is a coastal marine alga that forms dense stands in the Eastern Pacific, as well as off the coasts of South Africa, Australia, and New Zealand. Giant kelp anchors itself to the sea floor using a holdfast that tightly grips onto hard bottom, like a rocky reef. Kelp fronds can grow up to 45 meters long, but the maximum depth for an individual is about 30 meters, this is due to the limited sunlight where the newly settled microscopic kelp begin to grow. Waves are a major destructive force to kelp forests and can set its nearshore limit along rocky coastlines.
So now that we know the environment where kelp exists, we can use this information to better inform our kelp classification decisions. Let’s go through a few examples!
See these white (sometime blue) blobs along the coast? These are breaking waves. We know that breaking waves can be a major destructive force on a kelp forest, so you usually don’t see kelp where you see breaking waves. Remember, kelp forests will show up as green blobs. You can clearly see this large kelp forest growing just outside of the breaking waves.
This sure does look like a dense kelp forest, bright green blobs right off the coast, but in fact these are tidal mudflats. This can be one of the most difficult issues you may face. Algae or seagrass growing on these mudflats is going to show a similar green color as kelp, but we know that giant kelp only grows on hard seafloor, like rocks and boulders.
One way to make sure this is the right type of habitat for giant kelp is to use Google Maps or Google Earth. You can click on the coordinates above each image to automatically take you to a new page showing the approximate area of that image. Then, I like to copy just the coordinate numbers and paste them into the Google Maps search bar like, ‘38.557, -123.300’, this will place a pin on that exact location and show you a satellite image of the area with better spatial resolution.
Small islands off the coast can sometimes appear to be dense kelp forests. Again, if you are unsure, I recommend using the Google Maps trick I explained above. You should then be able to confirm whether or not the green blob is kelp or a small rock/island.
Giant kelp will never be growing in inland lakes or water bodies. This is a coastal marine species. If you see a green blob in a lake or some kind of inland river/delta/estuary/bay, it is probably something cool, but it is definitely not giant kelp. Again, if you are unsure, use the Google Maps link to see if the body of water you are looking at is coastal ocean or a lake/river/canal.
That is all for today! I am having a great time interacting with everyone on Zooniverse Talk, please keep the questions coming!