Viewing Phytoplankton From Space

Viewing Phytoplankton From Space

What a difference a month makes! I've downloaded some wonderful MODIS satellite imagery (brought to you by NASA) that measures the amount of chlorophyll in the water. Chlorophyll is a green pigment that powers photosynthesis inside plants and algae. Remember that photosynthesis is the process where the sun powers the conversion of carbon dioxide and water into sugars and oxygen. The hotter colors here in the April 17 image (bottom right) show that there is more phytoplankton in the water right now compared to the March 16 image (top left). You may be wondering how the camera is able to pick out the chlorophyll in all that blue water? The satellite is picking up on the red-light wavelengths emitted by the chlorophyll pigment at 680 and 720 nm.

Getting the satellite overhead on a cloudless day is a bit tricky, so if you notice a grey/black area, those are clouds. The people who do this remote sensing work have come up with very careful calibration methods for their image processing algorithms. Each region has undergone extensive testing to normalize for unique water quality properties like particulates in the water, depth, dissolved organic matter, and common algal pigments. As great as these satellite images are, there are limitations in how close a pixel can come to land. Dirt really interferes with a signal, particularly in Puget Sound which is why there is no color south of Tacoma. The more fine-scale the resolution of the camera on the satellite, the more useful future models will be to us.

These images came from the NANOOS website. Those folks at UW-APL (and a whole host of other partners) have been doing an amazing job creating this web tool to visualize the research on the Salish Sea. I visited it tonight because I wanted to download data from a PRISM research cruise I was on in the fall of 2009. I couldn't believe how much they had enhanced the site in the past few years. This image is of the chlorophyll at varying depths along the transect of Puget Sound main basin (red line) from North to South. The far left point is out beyond Dungeness Spit. It shows that there was a subsurface algae patch next to Port Townsend, and a denser algae patch down by Vashon Island.