Research about Island of Pohnpei

USGS2021

Using ALOS-2 synthetic aperture radar (SAR) and interferometric SAR to detect landslides on the mountainous island of Pohnpei, Federated States of Micronesia

This study was undertaken by the U.S. Geological Survey to assess the detectability of landslides in the densely forested and mountainous island of Pohnpei in the Federated States of Micronesia. The study used existing field-observed land-cover changes and landslides visible on Google Earth (GE) images. A limited number of ALOS-2 PALSAR-2 L-band synthetic aperture radar (SAR) images were collected on two adjacent orbit paths before and after an intense rainfall event that affected Pohnpei in mid-March 2018. Similar sets of images were collected in 2019 and 2020. Low coherence throughout the island interior eliminated use of phase-change products, and change analysis identified no landslide features as having formed in 2019 or 2020. The assessment of red-green-blue image composites and application of the log-ratio method to the 2018 ground-range SAR images identified 5 of the 11 landslides observed on the GE images. Visual comparisons of the co-event and post-event coherence image products detected 9 of the 11 landslides observed on the GE images. Combined, the ground-based SAR and interferometric SAR coherence change detections overcame high temporal and spatial decorrelations, identified all but one landslide visible in the GE comparison, and included substantial redundancy. The robustness of the landslide detection indicates that an increased collection frequency of L-band images could support systematic monitoring of land-cover change on Pohnpei at the scale reported in this study.

Island of Pohnpei↗

USGS2021

Sea-level rise vulnerability of mangrove forests on the Micronesian Island of Pohnpei

Introduction The mangrove forests across the Federated States of Micronesia provide critical resources and contribute to climate resilience. Locally, mangrove forests provide habitat for fish and wildlife, timber, and other cultural resources. Mangrove forests also protect Micronesian communities from tropical cyclones and tsunamis, providing a buffer against powerful waves and winds. Mangrove forests in Micronesia can store 700–1,800 metric tons of carbon per hectare (Donato and others, 2011), contributing to the estimated 5–10 billion metric tons of carbon stored by mangroves around the world (Alongi, 2018). This carbon storage is essential for global climate resilience. Mangrove forests and the benefits these ecosystems provide are threatened by accelerating sea-level rise and human activities. Healthy mangrove forests are resilient systems and have kept pace with some amounts of sea-level rise, but rapid sea-level rise could outpace the mangroves’ ability to adapt. Degraded mangroves are at greater risk where natural processes have been altered. Overharvest and clearing of timber, infrastructure development, and altered hydrology are just a few of the human activities that can damage mangrove forests.

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