4. Discussion
The temporal, spatial, and spectral characteristics of HyspIRI make this sensor particularly well suited to advance our understanding of giant kelp forest dynamics on local (< 1 km) to global scales. Monitoring giant kelp populations is challenging because, compared to many habitat-structuring primary producers, giant kelp forests are exceptionally dynamic (seeVariability in kelp canopy biomass below). In order to identify the processes that structure giant kelp population dynamics, researchers need observations of kelp populations that are both long-term and high frequency.
HyspIRI's planned 19-day VSWIR revisit time will enable the sensor to acquire at least 1 cloud free view per season of giant kelp habitat in nearly all regions of the world, thereby allowing us to resolve seasonal variability in giant kelp biomass and physiological condition (Table 1). This coverage will help researchers improve their understanding of the seasonal and interannual variability in giant kelp biomass and condition, the drivers of this variability, and its consequences for the ecosystem functioning of these forests. HyspIRI will help extend the record of remote kelp observations that is currently being built using historical Landsat imagery (Cavanaugh et al., 2011). If HyspIRI and a sensor such as Landsat 8 were both operational, we would be able to obtain between 3 and 5 observations of kelp canopy biomass per season for most of the regions that contain giant kelp. This approximately monthly coverage could be used to further refine our understanding of giant kelp biomass phenology. For example, discrete events such as wave disturbances are important drivers of giant kelp biomass dynamics. Higher temporal coverage would improve our ability to document the effects of these discrete events. Our estimates of seasonal cloud free coverage assumed 19- and 16-day revisit time (HyspIRI and Landsat 8 respectively) for all regions. In reality, the revisit times decrease poleward from the equator. As a result, our estimates of seasonal cloud free coverage are likely to be conservative.
Giant kelp typically occurs in large patches and HyspIRI's 60 m resolution will be sufficient to resolve patches > 3600 m2. A recent analysis of the metapopulation dynamics of giant kelp forests in southern California from Landsat 5 TM imagery found that 96% of the identified kelp patches were > 3600 m2 (Cavanaugh et al., 2014). Further work will be necessary to characterize kelp canopy detection limits using HyspIRI imagery. Researchers will be able to use techniques