Contribution of L-band SAR to systematic global mangrove monitoring

Abstract

cited By 8Information on the status of and changes in mangroves is required for national and international policy development, implementation and evaluation. To support these requirements, a component of the Japan Aerospace Exploration Agency?s (JAXA) Kyoto and Carbon (K&C) initiative has been to design and develop capability for a Global Mangrove Watch (GMW) that routinely monitors and reports on local to global changes in the extent of mangroves, primarily on the basis of observations by Japanese L-band synthetic aperture radar (SAR). The GMW aims are as follows: (1) to map progression of change within or from existing (e.g. Landsat-derived) global baselines of the extent of mangroves by comparing advanced land-observing satellite 2 (ALOS-2) phased array L-band SAR 2 (PALSAR-2) data from 2014 with that acquired by the Japanese earth resources satellite (JERS-1) SAR (1992?1998) and ALOS PALSAR (2006?2011); (2) to quantify changes in the structure and associated losses and gains of carbon on the basis of canopy height and above-ground biomass (AGB) estimated from the shuttle radar topographic mission (SRTM; acquired 2000), the ice, cloud and land-elevation satellite (ICESAT) geoscience laser altimeter system (GLAS; 2003?2010) and L-band backscatter data; (3) to determine likely losses and gains of tree species diversity through reference to International Union for the Conservation of Nature (IUCN) global thematic layers on the distribution of mangrove species; and (4) to validate maps of changes in the extent of mangroves, primarily through comparison with dense time-series of Landsat sensor data and to use these same data to describe the causes and consequences of change. The paper outlines and justifies the techniques being implemented and the role that the GMW might play in supporting national and international policies that relate specifically to the long-term conservation of mangrove ecosystems and the services they provide to society.Peer reviewe

The Global Mangrove Watch—A New 2010 Global Baseline of Mangrove Extent

“…To address the need for timely information on mangroves at a global level, the Japan Aerospace Exploration Agency (JAXA) Kyoto & Carbon (K&C) Initiative formulated the Global Mangrove Watch (GMW), which aimed to produce consistent 25 m spatial resolution maps of mangrove extent across their range by generating a baseline map for 2010. For mapping, Japanese L-band Synthetic Aperture Radar (SAR) data were considered most appropriate given their global coverage and sensitivity to the woody components of mangroves [12]. However, a limitation is that mangroves are often difficult to distinguish from other land covers (particularly forests and plantations) on the landward margins.…”

Measurement of Forest Above-Ground Biomass Using Active and Passive Remote Sensing at Large (Subnational to Global) Scales

“…Other factors complicating the retrieval of AGB include freeze/thaw conditions [69•], the presence of snow and cloud cover, and inundation below the forest. In the latter case, double bounce scattering [41] between tree trunks and the water surface enhances the SAR backscattered signal particularly at lower (e.g., L-band frequencies) and leads to overestimation of AGB.…”

“…In Australia, [41] improved estimates of AGB by combining SRTM-derived height maps with ALOS PALSAR backscatter data. All tall (> ∼10 m) mangroves with prop root systems supported a backscatter that was lower than those without and which decreased in proportion to the AGB.…”

Integrating Earth Observation Systems and International Environmental Regimes

“…Consider the example of the Global Mangrove Watch, developed by the Japan Aerospace Exploration Agency (JAXA) in partnership with, among others, the global NGO Wetlands International and offered as a tool for the Global Wetland Observing System under the Ramsar Convention (Rosenqvist et al 2014). Trends in mangrove cover can be highly relevant also for assessing progress or setbacks under UN conventions on climate change (UNFCCC), biodiversity (UNCBD) and conservation of migratory species of wild animals (Convention on the Conservation of Migratory Species of Wild Animals, CMS) (Lucas et al 2014). The JAXA initiative exploits the longevity of global-scale remote sensing at frequencies conducive to mangrove observation in combination with rapidly advancing data processing capacity.…”