Time series of quarterly kelp canopy extent from Landsat 5, 7, 8, and 9 since 1985

These data files represent a time series of surface kelp canopy area for giant kelp, Macrocystis pyrifera, and bull kelp, Nereocystis luetkeana, derived from atmospherically corrected Landsat imagery: Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Landsat 8 Operational Land Imager (OLI), and Landsat 9 Operational Land Imager 2 (OLI-2). Observations are made on a 16-day repeat cycle for each instrument, but temporal coverage can be irregular due to cloud cover, instrument failure, and the mission length of each sensor (TM: 1984–2011; ETM+: 1999–present; OLI/OLI-2: 2013–present).

The kelp canopy is composed of the portions of fronds and stipes floating on the surface of the water. Nearshore areas (within one Landsat pixel, ~30 m) and low-tide areas (both nearshore and offshore rocks) are masked during processing; therefore, kelp canopy area within those regions is excluded from this dataset. See Bell et al. (2020, 2023) for more details on methods.

Data are organized into GeoTIFF files and contain the quarterly percent detections for each Landsat pixel across the four sensors. For example, if there were five clear passes of a pixel and it was classified as kelp in four of them, the pixel value would be 80. Kelp presence data are provided for individual 30 × 30 meter pixels for coastal areas along the Central and North Coast of British Columbia, Canada.

These data are suitable for investigating kelp dynamics at large spatial scales, and consideration should be given to their use for any given analysis. For local-scale analyses where species-level data are needed, or where kelp is fringing and sparse, users should use higher spatial resolution imagery for mapping (e.g., fixed-wing or drone surveys).

The dataset is currently updated through 2023 and is under review. Dataset points of contact: Luba Reshitnyk, Henry Houskeeper, and Tom Bell.

For detailed methods refer to these articles:

Bell TW, Cavanaugh KC, Saccomanno VR, Cavanaugh KC, Houskeeper HF, Eddy N, et al. (2023) Kelpwatch: A new visualization and analysis tool to explore kelp canopy dynamics reveals variable response to and recovery from marine heatwaves. PLoS ONE 18(3): e0271477. https://doi.org/10.1371/journal.pone.0271477

Bell, T.W., Allen, J.G., Cavanaugh, K.C., & Siegel, D.A. (2020). Three decades of variability in California's giant kelp forests from the Landsat satellites. Remote Sensing of Environment, 238, 110811.