Abstract
Satellite remote sensing is a valuable tool to map and monitor the distribution of marine macrophytes such as seagrass and seaweeds that perform many ecological functions and services in coastal habitats. Various satellites have been used to map the distribution of these coastal bottom habitat-forming species, with each sensor providing unique benefits. In this study, we first explored optimal methods to create bottom habitat maps using WorldView-3 satellite imagery. We secondly compared the WorldView-3 bottom habitat maps to previously produced Sentinel-2 maps in a temperate, optically complex environment in Nova Scotia, Canada to identify the top performing classification and the advantages and disadvantages of each sensor. Sentinel-2 provides a global, freely accessible dataset where four bands are available at a 10-m spatial resolution in the visible and near infrared spectrum. Conversely, WorldView-3 is a commercial satellite where eight bands are available at a 2-m spatial resolution in the visible and near infrared spectrum, but data catalogs are costly and limited in scope. Our optimal WorldView-3 workflow processed images from digital numbers to habitat classification maps, and included a semiautomatic stripe correction. Our comparison of bottom habitat maps explored the impact of improved WorldView-3 spatial resolution in isolation, and the combined advantage of both WorldView’s increased spatial and spectral resolution relative to Sentinel-2. We further explored the effect of tidal height on classification success, and relative changes in water clarity between images collected at different dates. As expected, both sensors are suitable for bottom habitat mapping. The value of WorldView-3 came from both its increased spatial and spectral resolution, particularly for fragmented vegetation, and the value of Sentinel-2 imagery comes from its global dataset that readily allows for large scale habitat mapping. Given the variation in scale, cost and resolution of the two sensors, we provide recommendations on their use for mapping and monitoring marine macrophyte habitat in Atlantic Canada, with potential applications to other coastal areas of the world.
Highlights
Introduction iationsMarine macrophytes are ecologically and commercially important species in coastal habitats
The inclusion of the satellite-derived bathymetry (SDB) layer was a strong driver of bottom habitat trends, with the resulting classification closely aligning with the SDB layer
We tested how the WorldView-3 bottom habitat maps produced at a 2-m resolution compared to a bottom habitat map produced from Sentinel-2 at a 10-m resolution
Summary
Introduction iationsMarine macrophytes are ecologically and commercially important species in coastal habitats. With the exception of one intertidal species (Ascophyllum nodosum; rockweed), macrophytes in Atlantic Canada do not form a surface floating canopy, but rather “populate” the seafloor at a wide range of depths (≤20 m). Seaweed- and seagrass-dominated ecosystems are highly productive habitats [1], providing multiple ecological functions and services including carbon storage, protection against coastal erosion, absorbing nutrient runoff, provision of biogenic habitat structure, as well as acting as an indicator of overall ecosystem health [2–6]. Given their ecological importance, tools for mapping and Licensee MDPI, Basel, Switzerland.
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