Browsing by Subject "Multi-scale"

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Characterizing ecosystem structural and functional properties in the central Kalahari using multi-scale remote sensing
(2014-05) Mishra, Niti Bhushan; Crews, Kelley A.
Understanding, monitoring and managing savanna ecosystems require characterizing both functional and structural properties of vegetation. Due to functional diversity and structural heterogeneity in savannas, characterizing these properties using remote sensing is methodologically challenging. Focusing on the semi-arid savanna in the central Kalahari, the objective of this dissertation was to combine in situ data with multi-scale satellite imagery and two image analysis approaches (i.e. Multiple Endmember Spectral Mixture Analysis (MESMA) and Object Based Image Analysis (OBIA)) to : (i) determine the superior method for estimating fractional photosynthetic vegetation (fPV), non-photosynthetic vegetation (fNPV) and bare soil (fBS) when high spatial resolution multispectral imagery is used, (ii) examine the suitability of OBIA for mapping vegetation morphology types using a Landsat TM imagery, (iii) examine the impact of changing spatial resolution on magnitude and accuracy of fractional cover and (iv) examine how the fractional cover magnitude and accuracy are spatially associated with vegetation morphology. Using the GeoEye-1 imagery, MESMA provided more accurate fractional cover estimates than OBIA. The increasing segmentation scale in OBIA resulted in a consistent increase in error. While areas under woody cover produced lower errors even at coarse segmentation scales, those with herbaceous cover provided low errors only at the fine segmentation scale. Vegetation morphology type mapping results suggest that classes with dominant woody life forms attained higher accuracy at fine segmentation scales, while those with dominant herbaceous vegetation reached higher classification accuracy at coarse segmentation scales. Contrarily, for bare areas accuracy was relatively unaffected by changing segmentation scale. Multi-scale fractional cover mapping results indicate that increasing pixel size caused consistent increases in variance of and error in fractional cover estimates. Even at a coarse spatial resolution, fPV was estimated with higher accuracy compared to fNPV and fBS. At a larger pixel size, in areas with dominant woody vegetation, fPV was overestimated at the cost of mainly underestimating fBS; in contrast, in areas with dominant herbaceous vegetation, fNPV was overestimated with a corresponding underestimation of both fPV and fBS. These results underscore that structural and functional heterogeneity in savannas impact retrieval of fractional cover, suggesting that comprehensive remote sensing of savannas needs to take both structure and cover into account.
An integrated computational-experimental approach for the in situ estimation of valve interstitial cell biomechanical state
(2016-05) Buchanan, Rachel Marie; Sacks, Michael S.; Baker, Aaron B; Stachowiak, Jeanne C; Moon, Tess J; Guilak, Farshid
Mechanical forces are known to regulate aortic valve interstitial cell (AVIC) functional state by modulating their biosynthetic activity, translating to differences in tissue composition and structure and, potentially, leading to aortic valve (AV) dysfunction. While advances have been made toward the understanding of AVIC behavior ex-situ, the AVIC biomechanical state in its native extracellular matrix (ECM) remains largely unknown. Consequently, changes in AVIC behaviors, such as stiffness and contractility, resulting from pathological cues in-situ remain unidentified. We hypothesize that improved descriptions of AVIC biomechanical state in-situ, obtained using an inverse modeling approach, will provide deeper insight into AVIC interactions with the surrounding ECM, revealing important changes resulting from pathological state, and possibly informing pharmaceutical therapies. To achieve this, a novel integrated numerical-experimental framework to estimate AVIC mechanobiological state in-situ was developed. Flexural deformation of intact AV leaflets was used to quantify the effects of AVIC stiffness and contraction at the tissue level. In addition to being a relevant deformation mode of the cardiac cycle, flexure is highly sensitive to layer-specific changes in AVIC biomechanics. As a first step, a tissue-level bilayer model that accurately captures the bidirectional flexural response of AV intact layers in a passive state was developed. Next, tissue micromorphology was incorporated in a macro-micro scale framework to simulate layer-specific AVIC-ECM interactions. The macro-micro AV model enables the estimation of changes in effective AVIC stiffness and contraction in-situ that are otherwise grossly inaccessible through experimental approaches alone. Finally, microindentation studies examining AVIC activation were run in parallel with in-situ studies to emphasize the necessity of an in-situ approach, and the advantage it affords over existing ex-situ methodology. In conclusion, the developed numerical-experimental methodology can be used to obtain AVIC properties in-situ. Most importantly, it can lead to further understanding of AVIC-ECM mechanical coupling under various pathophysiological conditions and the investigation of possible treatment strategies targeting the myofibroblast phenotype characteristic of early signs of sclerotic valvular disease.