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Wetlands are ecologically dynamic land areas that support more biological diversity than any other type of ecosystem on the planet. In addition to supporting an astonishing variety of plants and animals, wetlands filter and purify water, control flooding, and stabilize shorelines. However, as sources of fish, fuel, land, and water, wetlands are threatened around the globe as the demand for these resources grows. Remote sensing provides a means of identifying and observing changes occurring in these critical ecosystems.

Synthetic aperture radar (SAR) uses microwave energy to detect physical properties of the Earth’s surface. Unlike optical technology, SAR can image through darkness, clouds, and rain. The characteristics of SAR make it a particularly effective tool for measuring water inundation, seasonal variations in water levels or habitat, large-scale vegetation patterns, and the effects of natural or human disturbance on wetland areas.

Wetlands MEaSUREs Overview

Among the most biologically diverse of Earth’s ecosystems, wetlands cover only ∼5% of the Earth’s ice-free land surface but exert major impacts on global biogeochemistry, hydrology, and wildlife diversity. Encompassing systems ranging from inundated forests, swamps, lakes, rivers, saltmarshes, mangroves, and poorly-drained permafrost, wetlands dominate the global methane cycle through their sensitivity to interannual and longer-term climate fluctuations and play a unique role in the transformation of biogeochemical material and as wildlife habitats for numerous species. Inundated wetland areas’ extent and seasonal, interannual, and decadal variation play key roles in ecosystem dynamics.

Wetlands can be swamps, marshes, bogs, or fens. Despite the importance of these biomes in the global cycling of carbon and water and to current and future climate, and in part because of their complexity and inaccessibility, much about wetlands remains to be discovered, including how much of the planet they occupy and details of how they affect and are affected by climate. Remote sensing gives scientists powerful tools for collecting data on wetlands distribution and dynamics. These data enable researchers to map habitats, identify vegetation types, time the rise and fall of water levels, and more. Spaceborne microwave sensing is particularly sensitive to surface water and vegetation structure, supporting monitoring large, inaccessible areas over time regardless of atmospheric conditions or solar illumination.

Alaska Ecological Forecasting - NASA DEVELOP Fall 2018 at NASA's Jet Propulsion Laboratory

NASA MEaSUREs Data Through ASF DAAC

Through the Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, NASA supports developing and distributing Earth System Data Records (ESDR), developed from remote sensing datasets and expanding understanding of the Earth system. Emphasis is placed on linking observations from multiple satellites into coherent time series datasets. MEaSUREs projects generate coherent time series datasets and facilitate the synthesis of datasets to develop comprehensive Earth system models. MEaSUREs products are subject to rigorous standards for data quality, validation, algorithm description, documentation, and delivery.

NASA's Alaska Satellite Facility Distributed Active Archive Center (ASF DAAC) archives and distributes the ESDR datasets from the NASA Inundated Wetlands MEaSUREs project. These inundated wetlands ESDR datasets facilitate investigations on the role of wetlands in climate, biogeochemistry, hydrology, and biodiversity.

A map of Alaska wetlands shows the state in shades of green, tan, and orange, with orange indicating higher ground. The surrounding ocean is bright blue.

This landmark, high-resolution map of Alaska wetlands, published in 2009, was created with mosaics of ALOS PALSAR imagery. © JAXA 1993-1998

The inundated wetlands ESDR consists of two primary components:

  • Fine-resolution maps of wetland extent, vegetation type, and seasonal inundation dynamics derived from Synthetic Aperture Radar (SAR) for regional and continental-scale areas covering crucial wetlands systems. These are created using data from a variety of spaceborne SARs, including the Japan Aerospace Exploration Agency (JAXA) Phased Array L-Band SAR (PALSAR) sensor mounted on the Advanced Land Observing Satellite (ALOS) and the associated follow-on and predecessor missions ALOS-2 PALSAR-2, and JERS-1 (the Japanese Earth Resources Satellite-1), respectively. The wetlands datasets were generated using algorithms appropriate to the nature of the wetlands systems under study, including time series and statistically based tree classifiers.
  • Global, coarse-resolution time series mappings of inundated area fraction at ~25 km resolution derived from multiple satellite remote sensing observations, including passive and active microwave sensors and optical data sets optimized for inundation detection. The algorithm employed in generating this dataset employs a clustering model and a mixture model in the classification of fractional inundated areas. These datasets are provided bi-monthly for 1992-1999 and daily for 2000 onward. Annual summary products are provided, including the maximum inundated extent and annual inundation duration. A daily near real-time (NRT) dataset with 2-3 day latency is also provided.