Satellite sensor requirements for monitoring essential biodiversity variables of coastal ecosystems

Abstract

The biodiversity and high productivity of coastal terrestrial and aquatic habitats are the foundation for important benefits to human societies around the world. These globally distributed habitats need frequent and broad systematic assessments, but field surveys only cover a small fraction of these areas. Satellite‐based sensors can repeatedly record the visible and near‐infrared reflectance spectra that contain the absorption, scattering, and fluorescence signatures of functional phytoplankton groups, colored dissolved matter, and particulate matter near the surface ocean, and of biologically structured habitats (floating and emergent vegetation, benthic habitats like coral, seagrass, and algae). These measures can be incorporated into Essential Biodiversity Variables (EBVs), including the distribution, abundance, and traits of groups of species populations, and used to evaluate habitat fragmentation. However, current and planned satellites are not designed to observe the EBVs that change rapidly with extreme tides, salinity, temperatures, storms, pollution, or physical habitat destruction over scales relevant to human activity. Making these observations requires a new generation of satellite sensors able to sample with these combined characteristics: (1) spatial resolution on the order of 30 to 100‐m pixels or smaller; (2) spectral resolution on the order of 5 nm in the visible and 10 nm in the short‐wave infrared spectrum (or at least two or more bands at 1,030, 1,240, 1,630, 2,125, and/or 2,260 nm) for atmospheric correction and aquatic and vegetation assessments; (3) radiometric quality with signal to noise ratios (SNR) above 800 (relative to signal levels typical of the open ocean), 14‐bit digitization, absolute radiometric calibration <2%, relative calibration of 0.2%, polarization sensitivity <1%, high radiometric stability and linearity, and operations designed to minimize sunglint; and (4) temporal resolution of hours to days. We refer to these combined specifications as H4 imaging. Enabling H4 imaging is vital for the conservation and management of global biodiversity and ecosystem services, including food provisioning and water security. An agile satellite in a 3‐d repeat low‐Earth orbit could sample 30‐km swath images of several hundred coastal habitats daily. Nine H4 satellites would provide weekly coverage of global coastal zones. Such satellite constellations are now feasible and are used in various applications.

Coral Reef Monitoring, Reef Assessment Technologies, and Ecosystem-Based Management

“…There is much hope that in the not-too-distant future, coral reef Essential Biodiversity Variables (Muller-Karger et al, 2018b) may be collected with high radiometric quality satellite data at high spectral resolution, relatively high spatial resolution, and at high temporal frequency. Such observations, with high resolution in four dimensions, are referred to as H4 satellite observations (see Muller-Karger et al, 2018a). Integrating these data sources with in situ manned observations may provide unprecedented empowerment for managers of coral reef locations to understand the complexity of processes affecting their sites, and be able to respond to these with effective management tools.…”

Future Ocean Observations to Connect Climate, Fisheries and Marine Ecosystems

“…There needs to be more international coordination on measuring EOVs (Muller-Karger et al, 2018a). International exchange of climate data for ecosystems is important for countries that share ecosystems, but also for an understanding of similar ecosystems globally.…”

Flux towers in the sky: global ecology from space

“…Here, we review new observations that are expanding the ability to understand global terrestrial ecosystems; some equivalent advances in marine ecology are described elsewhere (Muller‐Karger et al ., ). We focus on space‐based measurements and key synergistic surface observing systems.…”