2 research outputs found

    Genetic constraints on temporal variation of airborne reflectance spectra and their uncertainties over a temperate forest

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    Remote sensing enhances large-scale biodiversity monitoring by overcoming temporal and spatial limitations of ground-based measurements and allows assessment of multiple plant traits simultaneously. The total set of traits and their variation over time is specific for each individual and can reveal information about the genetic composition of forest communities. Measuring trait variation among individuals of one species continuously across space and time is a key component in monitoring genetic diversity but difficult to achieve with ground-based methods. Remote sensing approaches using imaging spectroscopy can provide high spectral, spatial, and temporal coverage to advance the monitoring of genetic diversity, if sufficient relation between spectral and genetic information can be established. We assessed reflectance spectra from individual Fagus sylvatica L. (European beech) trees acquired across eleven years from 69 flights of the Airborne Prism Experiment (APEX) above the same temperate forest in Switzerland. We derived reflectance spectra of 68 canopy trees and correlated differences in these spectra with genetic differences derived from microsatellite markers among the 68 individuals. We calculated these correlations for different points in time, wavelength regions and relative differences between wavelength regions. High correlations indicate high spectral-genetic similarities. We then tested the influence of environmental variables obtained at temporal scales from days to years on spectral-genetic similarities. We performed an uncertainty propagation of radiance measurements to provide a quality indicator for these correlations. We observed that genetically similar individuals had more similar reflectance spectra, but this varied between wavelength regions and across environmental variables. The short-wave infrared regions of the spectrum, influenced by water absorption, seemed to provide information on the population genetic structure at high temperatures, whereas the visible part of the spectrum, and the near-infrared region affected by scattering properties of tree canopies, showed more consistent patterns with genetic structure across longer time scales. Correlations of genetic similarity with reflectance spectra similarity were easier to detect when investigating relative differences between spectral bands (maximum correlation: 0.40) than reflectance data (maximum correlation: 0.33). Incorporating uncertainties of spectral measurements yielded improvements of spectral-genetic similarities of 36% and 20% for analyses based on single spectral bands, and relative differences between spectral bands, respectively. This study highlights the potential of dense multi-temporal airborne imaging spectroscopy data to detect the genetic structure of forest communities. We suggest that the observed temporal trajectories of reflectance spectra indicate physiological and possibly genetic constraints on plant responses to environmental change

    Detection and Correction of Radiance Variations During Spectral Calibration in APEX

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    The airborne prism experiment (APEX) is an imaging spectrometer developed by a joint Swiss-Belgian consortium composed of institutes (University of Zurich, Flemish Institute for Technological Research) and industries (RUAG, OIP, Netcetera), supported by the European Space Agency's PRODEX programme. APEX is designed to support the development of future space-borne Earth observation systems by simulating, calibrating or validating existing or planned optical satellite missions. Therefore, periodic extensive calibration of APEX is one major objective within the project. APEX calibration under laboratory conditions is done at its dedicated calibration and characterization facility at the German Aerospace Center (DLR) in Oberpfaffenhofen, Germany. While environmental influences under laboratory conditions are reduced to a minimum, the effects of atmospheric absorption and the properties of the underlying calibration infrastructure may still influence the measurements and subsequently the accuracy of the sensor spectral response estimations. It is demonstrated that even a lightpath of \~2 m through the atmosphere or the monochromator grating can have significant impact on the spectral response estimation of the sensor. A normalization approach described in this letter is able to compensate for these effects. The correction algorithm is exemplarily demonstrated on actual measurements for the short wavelength-IR range channe
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