4,858 research outputs found
Deep phase modulation interferometry
We have developed a method to equip homodyne interferometers with the
capability to operate with constant high sensitivity over many fringes for
continuous real-time tracking. The method can be considered as an extension of
the "J_1...J_4" methods, and its enhancement to deliver very sensitive angular
measurements through Differential Wavefront Sensing is straightforward. Beam
generation requires a sinusoidal phase modulation of several radians in one
interferometer arm. On a stable optical bench, we have demonstrated a long-term
sensitivity over thousands of seconds of 0.1 mrad/sqrt[Hz] that correspond to
20 pm/sqrt[Hz] in length, and 10 nrad/sqrt[Hz] in angle at millihertz
frequencies
The Adaptive Transient Hough method for long-duration gravitational wave transients
This paper describes a new semi-coherent method to search for transient
gravitational waves of intermediate duration (hours to days). In order to
search for newborn isolated neutron stars with their possibly very rapid
spin-down, we model the frequency evolution as a power law. The search uses
short Fourier transforms from the output of ground-based gravitational wave
detectors and applies a weighted Hough transform, also taking into account the
signal's amplitude evolution. We present the technical details for implementing
the algorithm, its statistical properties, and a sensitivity estimate. A first
example application of this method was in the search for GW170817 post-merger
signals, and we verify the estimated sensitivity with simulated signals for
this case.Comment: 13 pages, 14 figure
A direct helicopter EM sea ice thickness inversion, assessed with synthetic and field data
Accuracy and precision of helicopter electromagneticHEM sounding are the essential parameters for HEM seaicethickness profiling. For sea-ice thickness research, thequality of HEM ice thickness estimates must be better than10 cm to detect potential climatologic thickness changes.Weintroduce and assess a direct, 1D HEM data inversion algorithmfor estimating sea-ice thickness. For synthetic qualityassessment, an analytically determined HEM sea-ice thicknesssensitivity is used to derive precision and accuracy. Precisionis related directly to random, instrumental noise, althoughaccuracy is defined by systematic bias arising fromthe data processing algorithm. For the in-phase component ofthe HEM response, sensitivity increases with frequency andcoil spacing, but decreases with flying height. For small-scaleHEM instruments used in sea-ice thickness surveys, instrumentalnoise must not exceed 5 ppm to reach ice thicknessprecision of 10 cm at 15-m nominal flying height. Comparableprecision is yielded at 30-m height for conventional explorationHEM systems with bigger coil spacings. Accuracylosses caused by approximations made for the direct inversionare negligible for brackish water and remain better than10 cm for saline water. Synthetic precision and accuracy estimatesare verified with drill-hole validated field data fromEast Antarctica, where HEM-derived level-ice thicknessagrees with drilling results to within 4%, or 2 cm
Automatic detection of crop rows in maize fields with high weeds pressure
This paper proposes a new method, oriented to crop row detection in images from maize fields with high weed pressure. The vision system is designed to be installed onboard a mobile agricultural vehicle, i.e. submitted to gyros, vibrations and undesired movements. The images are captured under image perspective, being affected by the above undesired effects. The image processing consists of three main processes: image segmentation, double thresholding, based on the Otsu’s method, and crop row detection. Image segmentation is based on the application of a vegetation index, the double thresholding achieves the separation between weeds and crops and the crop row detection applies least squares linear regression for line adjustment. Crop and weed separation becomes effective and the crop row detection can be favorably compared against the classical approach based on the Hough transform. Both gain effectiveness and accuracy thanks to the double thresholding that makes the main finding of the paper
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