Japan's Aerospace Exploration Agency (JAXA’s) Kyoto and Carbon (K&C) Initiative (Rosenqvist et al. 2010) has developed capability for a Global Mangrove Watch (GMW; JAXA 2013), primarily using Japanese L-band SAR data. The approach adopted by the GMW was first to establish a baseline map of mangroves for 2010 at a global level through a random forests classification of both Landsat sensor spectral composite data (all spectral wavebands) and Advanced Land Observing Satellite (ALOS) Phased Arrayed L-band Synthetic Aperture Radar (SAR) data. The use of both optical and radar data benefited the random forest classification as these are sensitive to differences in the species composition, cover and also distribution of woody (branch, trunk and root) material. Changes away from and within this baseline were subsequently derived for 1996 (JERS-1) 2007, 2008, 2009 (ALOS PALSAR), 2015 and 2016 (ALOS-2 PALSAR-2) using a histogram thresholding approach (Thomas et al., 2017), with these data reflecting losses or gains in mangrove wood volume/biomass. The GMW maps were considered to be a robust estimate of the extent of mangroves as they integrated both optical and radar sensors for the period of observation. No mapping was available prior to 1996.
The GMW maps of global mangrove extent are available on the World Resources Institute (WRI) Global Forest Watch (GFW) server: https://www.wri.org/insights/satellite-data-reveals-state-worlds-mangrove-forests
and for download at the WCMC Ocean Data Viewer.
For Australia, these have been replaced by mapping generated these same epochs through Digital Earth Australia by thresholding Landsat-derived Persistent Green Fraction converted to Planimetirc Canopy Cover (%) with a boundary area representing the union of the GMW layers for 1996, 2007-2010 and 2015/16. These datasets will be released in the autumn of 2018 and will soon be accessible through the following links.