Ohia SAR Research

An Ecological Synthetic-aperature Radar Application

Introduction

The dominant and cornerstone tree species of Hawai’i is the Ohia, Metrosideros polymorpha. Hundreds of endemic flora and fauna are completely reliant on it for survival. In the early 2010s, many of these trees were seen dying rapidly and their leaves browning. The cause of this was found to be a fungal pathogens, Ceratocystis lukuohia and C. huliohia, commonly called Rapid Ohia Death (ROD). The current distribution of ROD is shown below.

ROD distribution on the Big Island, Oahu, and Kaua'i

The current method of tracking the distribution of ROD is via airborne flyovers which take place ~1/365days due to the high resources necessary.

Airborne flight lines 2016-2021 and pilot performing ROD obervations.

The 365 day observation windows leave large gaps for improvement. If satellites had the capability to detect changes in Ohia health, the time between detections could drop from 365 days to a single day, a 99.7% time reduction. I am researching the feasability of a certain type of Radar system called Synthetic-aperature Radar for ROD detection. SAR can “see” through clouds, observe during nighttime, and detect incredibly small changes in the observed object.

Capella X-band SAR and the endemic 'I'iwi on an Ohia.

To determine the feasibility of this technology, I am simulating the forest canopy and its reflection. In June, I submitted a paper with Dr. Sean Peters to the 2026 AIAA SciTech Forum detailing how the changed reflectivity between healthy and infected trees is significant enough for SAR detection. This paper was accepted on August 25th, and I will present early January in Orlando.

A 2D relfecitivy map of simulated Ohia canopy with brown trees representing ROD, and green trees representing healthy Ohia. Dark squares show low reflectivity while white squares represent high reflectivity.

Now I am working on a drastically improved simulation which takes into account a 3D scene with a real satellite path simulating transmitted pulse and reception from the scene.