Hyperspectral and multispectral satellite data analysis of nitrogen in grazed and ungrazed tundra in Långfjället, Sweden
Abstract
Reindeer are a keystone species in the circumpolar north, where they hold great cultural and
ecological importance. Continued climate change threatens the long-term sustainability of
reindeer husbandry. Reindeer can affect the tundra landscape, influencing the soil nutrient
cycling, including the soil nitrogen availability. Hyperspectral remote sensing of biochemical
traits is a relatively new but promising field of study. This thesis aims to investigate if
hyperspectral and multispectral satellite data could be used to differentiate between grazed and
ungrazed tundra landscape, as well as to determine which hyperspectral wavelength bands are
best suited to estimate nitrogen content over a tundra reindeer grazing site. A hyperspectral
satellite, PRIMSA, and a multispectral satellite, Sentinel-2, were used over a heath shrub study
site in Sweden. A visual comparison of the spectral curves from PRISMA and Sentinel-2 were
used to differentiate between grazed and ungrazed tundra landscape. A variety of remote
sensing analysis methods, i.e., PCA, RF regression, RF classification, MLR, and an
unsupervised classification, as well as a standard C/N ratio analysis of 24 plant samples were
used to get a final map over estimated nitrogen content. The result from this study supports
using chlorophyll as a proxy for nitrogen content. From the MLR, all PRISMA wavelength
bands below 680 nm (band 35) had R2 values >0.7. In particular, this study identified that band
1, at 405 nm, was best suited for determining nitrogen content over a tundra reindeer grazing
site. Neither PRIMSA nor Sentinel-2 were definitively found to be better at differentiating
between grazed and ungrazed rangeland. Although this project was limited by the small sample
size of the reference data, it shows potential possibilities of what could be done with
biochemical trait estimation via remote sensing. Contributing to the wider scientific field by
giving a suggested method for estimating nitrogen content and by giving a suggestion for which
hyperspectral wavelength band is best suited for determining nitrogen content in a tundra
landscape.
Degree
Student essay
Collections
View/ Open
Date
2023-08-18Author
Dahlstedt, Emma
Keywords
Hyperspectral imaging
Imaging spectroscopy
Nitrogen
Reindeer
Herbivory
Tundra
Grazing
Series/Report no.
B1263
Language
eng