Ultrasound Imaging by Thermally Tunable Phononic Crystal Lens

This work demonstrates the detections and mappings of a solid object using a thermally tunable solid-state phononic crystal lens at low frequency for potential use in future long-distance detection. The phononic crystal lens is infiltrated with a polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) bulk hydrogel polymer. The hydrogel undergoes a volumetric phase transition due to a temperature change leading to a temperature-dependent sound velocity and density. The temperature variation from 20 °C to 39 °C changes the focal length of the tunable solid-state lens by 1 cm in the axial direction. This thermo-reversible tunable focal length lens was used in a monostatic setup for one- and two-dimensional mapping scans in both frequency domain echo-intensity and temporal domain time-of-flight modes. The experimental results illustrated 1.03 ± 0.15λ and 2.35 ± 0.28λ on the lateral and axial minimum detectable object size. The experiments using the tunable lens demonstrate the capability to detect objects by changing the temperature in water without translating an object, source, or detector. The time-of-flight mode modality using the tunable solid-state phononic lens increases the signal-to-noise ratio compared to a conventional phononic crystal lens.

Multidecadal elevation changes from spy satellite images: application to glaciers and landslides

<p><span>Earth’s surface has evolved dramatically over the last 50 years as a consequence of anthropogenic activities and climate change. The observation of such changes at decadal scales is often limited to sparse in-situ observations. The growth of satellite remote-sensing has enabled such monitoring at regional/global scales but generally over less than two decades.</span></p><p><span>More than 2 million images have been acquired by American reconnaissance (“spy”) satellites </span><span>on photographic film</span><span> from the 1960s to the 1980s, and progressively declassified. </span><span>W</span><span>ith </span><span>near-global coverage and</span><span> meter to sub-meter resolution, </span><span>these images have a large potential for many geoscience applications. However </span><span>the photographic archive represents a unique set of challenges: pre-processing of the scans, correction of the image distortion caused during storing and scanning, </span><span>poorly</span><span> known camera position</span><span>s</span><span> and parameters. </span><span>The vast majority of studies using these data rely on tedious manual processing of the data, hindering regional scale applications.</span></p><p><span>Here</span><span>, we present the existing datasets and</span><span> the development of an </span><span>automated </span><span>processing</span><span> pipeline</span><span>. We will focus in particular on images acquired </span><span>by </span><span>the Hexagon mapping camera (1973-1980, </span><span>12 missions</span><span>) at 6-9 m ground resolution. A fully automated workflow has been developed to detect the 1081 fiducial markers present on the image, correct for distortion and stitch the different parts of the image, scanned in multiple sections. The pre-processed images are then </span><span>used </span><span>to generate Digital Elevation Models (DEMs) at 24 m resolution</span><span> with</span><span> the </span><span>open-source </span><span>NASA Ames Stereo Pipeline. The </span><span>developed workflow </span><span>is able to automatically solve </span><span>for</span> <span>the unknown </span><span>camera position</span><span>s/</span><span>orientation</span><span>s</span><span> and optimally aligns </span><span>the DEMs </span><span>to an ancillary DEM for </span><span>the </span><span>determination of elevation change</span><span>s</span><span>. </span><span>The application to ~600 images has revealed systematic biases in the retrieved elevation, up to 30 m error, linked to uncertainties in the camera parameters (focal length, lens distortion). We present a methodology to refine these parameters using an ancillary DEM only, without use of manual Ground Control Points. The KH-9 elevation is then validated against existing maps in Europe and Alaska and shows a </span><span>vertical accuracy of </span><span>~5 m </span><span>(68% interval) to 10-15 m (95% interval)</span><span>, </span><span>sufficient for the study of large surface deformation (glaciers, landslides).</span></p><p><span>Finally, we conclude with several use of these data for the estimation of 40 years geodetic glacier mass balance in Europe and Alaska, and irrigation-triggered landslides in South Peru.</span></p>

Decoupling of the position and angular errors in laser pointing with a neural network method

In laser-pointing-related applications, when only the centroid of a laser spot is considered, then the position and angular errors of the laser beam are often coupled together. In this study, the decoupling of the position and angular errors is achieved from one single spot image by utilizing a neural network technique. In particular, the successful application of the neural network technique relies on novel experimental procedures, including using an appropriate small-focal-length lens and tilting the detector, to physically enlarge the contrast of different spots. This technique, with the corresponding new system design, may prove to be instructive in the future design of laser-pointing-related systems.

Assessing a 35mm Fixed-Lens Sony Alpha-5100 Intrinsic Parameters Prior to, During, and Post UAV Flight Mission

A fixed focal length lens (FFL) camera with on-adjustable focal length is common companions for conducting aerial photography using unmanned aerial vehicles (UAVs) due to its superiority on optical quality and wider maximum aperture, lighter weight and smaller sizes. A wide-angle 35mm FFL Sony a5100 camera had been used extensively in our recent aerial photography campaign using UAV. Since this off-the-self digital camera is categorized into a non-metric one, a stability performance issue in terms of intrinsic parameters raises a considerably attention, particularly on variations of the lens principal distance and principal point’s position relative to the camera’s CCD/CMOS sensor caused by the engine and other vibrations during flight data acquisitions. A series of calibration bundle adjustment was conducted to determine variations in the principal distances and principal point coordinates before commencing, during, and after accomplishment of the flight missions. This paper demonstrates the computation of the parameters and presents the resulting parameters for three different epochs. It reveals that there are distinct discrepancies of the principal distances and principal point coordinates prior to, during, and after the mission, that peaked around 1.2mm for the principal distance, as well as around 0.4mm and 1.3mm along the x-axis and the y-axis of the principal point coordinates respectively. In contrast, the lens distortions parameters show practically no perturbations in terms of radial, decentering, and affinity distortion terms during the experiments.