102 research outputs found
Investigation of smooth wave fronts using SLM-based phase retrieval and a phase diffuser
A phase retrieval technique using a spatial light modulator (SLM) and a phase
diffuser for a fast reconstruction of smooth wave fronts is demonstrated
experimentally. Diffuse illumination of a smooth test object with the aid of a
phase diffuser (maximum phase shift, Df = 0.85p) results in a significant
diversity in the intensity measurements which, in turn, is beneficial for a
non-stagnating iterative phase reconstruction. The use of the SLM enables
accurate and fast speckle intensity recording and active correction of
misalignments in the setup. The effectiveness of the technique is demonstrated
in the optical testing of lenses.Comment: The paper has been presented in 1st EOS Topical Meeting on Micro-and
Nano-Optoelectronic Systems, Bremen, Germany, 7 - 9 December 201
Non-destructive testing of carbon reinforced plastics by means of phase retrieval
In this work, the SLM-based phase retrieval system will be used to inspect
carbon reinforced plastics samples (CFRP) under applying a thermal load. For
this purpose, the system is used to capture a sequence of 8 spatially separated
recording planes, where the distance between subsequent planes equals 2 mm. For
detecting the hidden failures two sets of intensity observations are recorded.
The first set for the initial state and the second set is captured after
applying the load. To recover the phase information associated with the two
states, the captured intensities have been subjected to an iterative algorithm
based on the method of generalized projection.Comment: Conf. Speckle 201
Estimating lichen volume and reindeer winter pasture quality from Landsat imagery
Reindeer and caribou are keystone species in the circumpolar region, and rely on lichens as their main winter forage to survive in some of the most extreme environments on Earth. Lichen mats, however, can be heavily overgrazed at high deer densities, triggering area abandonment or population declines. Although the species' management and conservation require precise information on the quality of winter grazing areas, no reliable and cost-efficient methods are available to date to measure lichen volume across wide and remote areas. We developed a new Lichen Volume Estimator, LVE, using remote sensing and field measurements. We used a Landsat TM land cover mask to separate lichen heath communities from other vegetation types and, therein, we predicted lichen volume from a two dimensional Gaussian regression model using two indexes: the Normalized Difference Lichen Index, NDLI (Band 5−Band 4 / Band 5+Band 4), and the Normalized Difference Moisture Index, NDMI (Band 4−Band 5 / Band 4+Band 5). The model was parameterized using 202 ground measurements equally distributed across a gradient ranging from 0 to 80 lichen dm3/m2 (R2=0.74 between predicted and observed ground measurements), and was validated with a ten-fold cross validation procedure (R2=0.67), which also showed a high parameter stability. The LVE can be a valuable tool to predict the quality of winter pastures for reindeer and caribou and, thus, help to improve the species' management and conservation. Remote sensing Habitat mapping Reindeer Lichen volume and biomass Winter pasturespublishedVersio
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