Evaluation of sensor characteristics on the retrieval of vegetation
surface reflectance in high-latitude ecosystems
Abstract
Over the last nearly five decades, optical remote sensing has played a
key role in monitoring and quantifying global change, plant diversity,
and vegetation functioning across Earth’s terrestrial biomes. As a key
tool for researchers, land managers, and policy makers, optical remote
sensing facilitates scaling, mapping, and characterizing surface
properties over large areas and through time. In addition, steady
technological improvements have led to transformational changes in our
ability to understand ecosystem state and change, particularly through
the expansion of high spectral resolution (i.e. spectroscopic) remote
sensing platforms. Point and imaging spectroscopy systems have been used
across a range of scales, vegetation types, and biomes to infer plant
diversity, leaf traits, and ecosystem functioning. However, despite the
acknowledged utility of spectroscopic systems, data availability has
been limited to smaller geographic regions given a number of technical
challenges, including issues related to data volume and limited spatial
coverage by previous Earth Observing (EO) missions (i.e. Hyperion). The
NASA Surface Biology and Geology (SBG) mission is designed to fill this
gap in ecosystem monitoring. As part of the Space-based Imaging
Spectroscopy and Thermal pathfindER (SISTER) and Modeling end-to-end
traceability (MEET) SBG efforts, we used field, unoccupied aerial system
(UAS), and airborne imagery (from NASA’s AVIRIS-NG plafrom) to evaluate
the impacts of proposed and theoretical sensor instrument properties on
the retrieval of vegetation reflectance across tundra, shrub, and
treeline ecosystems in Alaska. Existing observations and open-source
tools are used for the simulation of surface reflectance under a range
of atmospheric conditions, vegetation types, and different sensor
properties. We find that retrieval uncertainty is reduced across all
surface types with increasing detector signal-to-noise (SNR) but also
key differences across different plant types. Results were also strongly
tied to sun-sensor geometry and atmospheric state. Through this exercise
we highlight key outcomes to consider for the SBG mission to optimize
surface reflectance retrieval in high latitudes that will help to
minimize errors in down-stream algorithms, such as functional trait
retrievals.