Watching from Space

Satellite view of SBC-LTER
Giant kelp canopy off the coast of Santa Barbara, as viewed by Landsat 5

The relatively recent emergence of satellites to characterize the earth’s surface has led to significant advances in the environmental sciences that affect our everyday life (witness Google Earth). The large spatial coverage obtained from satellites and aircraft enable regional and global comparisons at time scales that would be near impossible to obtain from ground-based surveys. As a result geographers and landscape ecologists are now able to assess the effects of human activities, natural disturbance, and climate change on changes in land cover, type, and use. Similarly, recent advances in the remote sensing of the ocean’s color provide high frequency data on sea surface temperature, phytoplankton abundance and water clarity across the globe. Unlike systems on land, most marine habitats are not amenable to being surveyed from the air due to the fact that they persist underwater. Giant kelp forests, which are found in temperate seas throughout the world, are somewhat unique in this regard as giant kelp extends through the water column to form a dense canopy at the sea surface that is detectable from the air, making it one of the few marine habitats that can be routinely quantified using remote sensing. With co-funding from NASA, SBC LTER researchers developed a novel method of measuring the canopy area and biomass of giant kelp from SPOT and Landsat satellites. This method entailed comparing satellite reflectance signals to our monthly diver-based measurements of kelp biomass in long-term study plots. Giant kelp forests are especially sensitive to environmental changes and have a history of undergoing abrupt, dramatic declines and increases in response to a variety of climatic and human-induced factors. The application of our remote sensing methods to the long-term (continuous since 1984), high frequency (~ once per month) global coverage of Landsat imagery is providing a unique opportunity for studying these dynamics over spatial and temporal scales that were previously impossible to examine. The recent decision to make Landsat data available to the public at no charge has greatly facilitated our use of this phenomenal resource for investigating giant kelp forests and is proving to be an invaluable tool in marine spatial planning and evaluation of recently established no-take marine reserves.