Pixel Walking: Ground-truth validation of NASA’s MODIS greening estimates in northwest Alaska


Toshio Matsuoka

Climate is changing most rapidly in the polar regions and mountains of the world. The Brooks Range as the northernmost mountain range in North America is expected to be changing at one of the fastest paces on Earth. The Landsat program is a satellite that has been continuously recording spectral information of the Earth’s surface since the early 1970’s. It takes the Landsat satellites 16 days to make a full orbit around the planet. Each day the satellite (Landsat 8) records roughly 24 million km2 of spectral information from the Earth’s surface that range from visible light to thermal infrared. From Landsat imagery researchers can calculate the Normalized Vegetation Index (NDVI). NDVI is the balance of red light and near infrared, which indicates the greenness of an area. By investigating the trend in maximum NDVI values, researchers like Dr. Logan Berner (Berner, et al. 2021) of Northern Arizona University and a collaborator with Prof. Roman Dial at Alaska Pacific University where I am a rising junior, hypothesize that vegetation is changing across landscapes at a resolution of 30-m by 30-m. A “greening” pixel is an area that increases in NDVI value, and a “browning” pixel (Verbyla, et al. 2008) decreases in NDVI value. Because NDVI trend is only a measure of the balance between two wavelengths of light over time, it is unknown what changes in vegetation are actually taking place in these greening and browning pixels (Raynolds, et al. 2008). By ground-truthing and collecting Arctic vegetation classifications and wood samples, such as tree and shrub rings, across the Brooks Range, we can better interpret these greening and browning trends recorded by the Landsat program in the context of climate change’s effects on this sensitive ecological region.


Name: Toshio Matsuoka, Undergraduate Student

Institution: Alaska Pacific University

Major: Marine and Environmental Sciences and Environmental Public Health

Mentor: Dr. Roman Dial, roman@alaskapacific.edu

Award: Apprenticeship

Funding Period: 2021 to 2022