scholarly journals DESIGN AND IMPLEMENT OF A CONICAL AIRBORNE LIDAR SCANNING SYSTEM

2020 ◽  
Vol XLII-3/W10 ◽  
pp. 1247-1252
Author(s):  
H. C. Hu ◽  
G. Q. Zhou ◽  
X. Zhou ◽  
Y. Z. Tan ◽  
J. D. Wei
Keyword(s):  
Single Point ◽  
Airborne Lidar ◽  
Field Of View ◽  
Scanning System ◽  
Dual Frequency ◽  
Scanning Device ◽  
Scanning Area ◽  
Laser Frequencies ◽  
Low Dispersion ◽  
Scanning Density

Abstract. At present, the main LiDAR is single-point lidar. APD arrays and laser arrays are restricted to exit, so the number of area array LiDAR is scarce. Single-point lidar can't form a scanning pattern with only one laser point on the ground after launching laser, so it must have a set of scanning device for single-point lidar. The scanning device designed in this paper forms a circular scanning area on the ground by rotating the refraction prism, and at the same time forms a conical field of view. At present, marine LiDAR uses this kind of scanner more frequently. The advantages of this scanner are: simple mechanical structure and smooth operation. Overlapping elliptical scanning trajectories can be obtained during flight, which increases scanning density. Ultra-low dispersion glass is used as refractive prism in this paper. In a certain range of laser frequencies, the refractive prism has almost the same effect on laser refraction at different frequencies. The simulation results show that the scanner can be used as a common LiDAR scanner or a dual-frequency LiDAR scanner.

A Comparison of 2-D Molecular Tagging Velocimetry (MTV) and Micro Particle Image Velocimetry (µPIV) for Microscale Flows

2010 ◽  
Author(s):  
Farhan Ahmad ◽  
Mona Abdolrazaghi ◽  
David S. Nobes
Keyword(s):  
Laser Beam ◽  
Flow Velocity ◽  
Laser Scanning ◽  
Imaging System ◽  
Single Point ◽  
Field Of View ◽  
Scanning System ◽  
Molecular Tagging Velocimetry ◽  
Molecular Tagging ◽  
Micro Particle Image Velocimetry

A 2-D scanning molecular tagging velocimetry technique is presented. The described MTV technique utilizes a scanning laser system enabling two-dimensional flow velocity measurements. The laser scanning system allows the tagging of molecules seeded in the flow of any desired pattern. This array of small dot markers in the region of interest is visualized using an epi-fluorescent optical imaging system. The scanning system facilitates the convenient maneuvering of the laser beam allowing the tagging of either a single point or a pattern. The laser beam is focused onto a single point leading to a more efficient tagging process. A standard particle tracking velocimetry (PTV) approach is used to resolve the two components of the flow velocity. Results obtained show the capability of the designed system to tag a region in the centre of the field of view. The tagging laser will be moved to any desired location within the field of view to tag the desired region.

scholarly journals Conditioning and PPP processing of smartphone GNSS measurements in realistic environments

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Ganga Shinghal ◽  
Sunil Bisnath
Keyword(s):  
Single Point ◽  
A Priori ◽  
Density Ratio ◽  
Satellite System ◽  
Quality Parameters ◽  
Urban Environments ◽  
Dual Frequency ◽  
Missing Measurements ◽  
Data Gaps ◽  
Point Positioning

AbstractSmartphones typically compute position using duty-cycled Global Navigation Satellite System (GNSS) L1 code measurements and Single Point Positioning (SPP) processing with the aid of cellular and other measurements. This internal positioning solution has an accuracy of several tens to hundreds of meters in realistic environments (handheld, vehicle dashboard, suburban, urban forested, etc.). With the advent of multi-constellation, dual-frequency GNSS chips in smartphones, along with the ability to extract raw code and carrier-phase measurements, it is possible to use Precise Point Positioning (PPP) to improve positioning without any additional equipment. This research analyses GNSS measurement quality parameters from a Xiaomi MI 8 dual-frequency smartphone in varied, realistic environments. In such environments, the system suffers from frequent phase loss-of-lock leading to data gaps. The smartphone measurements have low and irregular carrier-to-noise (C/N0) density ratio and high multipath, which leads to poor or no positioning solution. These problems are addressed by implementing a prediction technique for data gaps and a C/N0-based stochastic model for assigning realistic a priori weights to the observables in the PPP processing engine. Using these conditioning techniques, there is a 64% decrease in the horizontal positioning Root Mean Square (RMS) error and 100% positioning solution availability in sub-urban environments tested. The horizontal and 3D RMS were 20 cm and 30 cm respectively in a static open-sky environment and the horizontal RMS for the realistic kinematic scenario was 7 m with the phone on the dashboard of the car, using the SwiftNav Piksi Real-Time Kinematic (RTK) solution as reference. The PPP solution, computed using the YorkU PPP engine, also had a 5–10% percentage point more availability than the RTK solution, computed using RTKLIB software, since missing measurements in the logged file cause epoch rejection and a non-continuous solution, a problem which is solved by prediction for the PPP solution. The internal unaided positioning solution of the phone obtained from the logged NMEA (The National Marine Electronics Association) file was computed using point positioning with the aid of measurements from internal sensors. The PPP solution was 80% more accurate than the internal solution which had periodic drifts due to non-continuous computation of solution.

scholarly journals A Set of Grisms for FORS

1995 ◽  
Vol 149 ◽  
pp. 27-28 ◽  
Author(s):  
W. Fürtig ◽  
W. Seifert
Keyword(s):  
Wavelength Range ◽  
Field Of View ◽  
Parallel Beam ◽  
First Order ◽  
Large Telescopes ◽  
The University ◽  
Low Dispersion

The University Observatories of München and Göttingen and the Landessternwarte Heidelberg are building in cooperation with ESO two almost identical FOcal Reducer /low-dispersion Spectrographs (FORS) for the ESO Very Large Telescopes. FORS allows low-dispersion multiobject spectroscopy (19 slits) and longslit spectroscopy in the wavelength range of 330 to 1100 nm. A set of standard grisms with reciprocal dispersions of 45 ...230 Å/mm working in the first order are foreseen. With a slitwidth of 1 arcsec the resulting spectral resolutions range from 180 to 1800.For further FORS details see Appenzeller and Rupprecht (1992) and Seifert et al. (1994).The standard grisms are located in a grism wheel in the parallel beam between the collimator and the camera. Seven of eight positions are available for grisms. The free diameter of the grisms is 135 mm to cover the whole field of view of FORS. To avoid reflection ghosts the entrance surfaces are all tilted by .

scholarly journals Application of IGS Products for Air Navigation

2017 ◽  
Vol 24 (1) ◽  
pp. 285-300
Author(s):  
Henryk Jafernik ◽  
Janusz Ćwiklak ◽  
Kamil Krasuski ◽  
Jarosław Kozuba
Keyword(s):  
Least Squares Method ◽  
Single Point ◽  
Mean Value ◽  
Dual Frequency ◽  
Static Mode ◽  
Precise Positioning ◽  
Gps Satellites ◽  
Precise Ephemeris ◽  
Method Accuracy ◽  
Gps Observations

Abstract Single Point Positioning (SPP) method is widely used in air, marine, and land navigation to determine the user’s position in real time and post factum. A typical accuracy for this method of determining the user’s position in the static mode is approximately 10 meters. In air operations, the SPP method accuracy can be several times lower and that may cause problems with precise positioning of an aircraft. The authors of this article presented preliminary results of research concerning aircraft positioning in the kinematic mode based on GPS observations. For this purpose, an in-flight experiment, in which a Cessna 172 aircraft was used, was performed at the airport in Mielec, Poland. The aircraft was equipped with a dual-frequency Topcon TPS HiperPro receiver, which was recording satellite observations with 1-second interval. The aircraft position was determined using the least-squares method (LSM) in the RTKLIB (RTKPOST module) software. Two research tests were performed within the scope of the experiment, i.e. in test I the aircraft position was determined on the basis of raw GPS observations and the broadcast ephemeris data whereas in test II precision products of the IGS were used, such as: precise ephemeris SP3, DCB hardware delay, clock bias data of GPS satellites and receivers in the CLK format, data of the ionosphere maps based on IONEX format, and phase center calibration of GPS satellites and receivers in the ANTEX format. The use of the IGS precision products improved the accuracy of the X coordinate to 1 m, Y to 0.7 m and Z to 1.3 m. On the basis of tests I and II, an additional RMS-3D parameter was determined, whose mean value was 4 m.

scholarly journals DEVELOPMENT AND EVALUATION OF A UAV BASED MAPPING SYSTEM FOR REMOTE SENSING AND SURVEYING APPLICATIONS

2015 ◽  
Vol XL-1/W4 ◽  
pp. 233-239 ◽  
Author(s):  
C. Eling ◽  
M. Wieland ◽  
C. Hess ◽  
L. Klingbeil ◽  
H. Kuhlmann
Keyword(s):  
Remote Sensing ◽  
Reference Point ◽  
Time Synchronization ◽  
Low Cost ◽  
Single Point ◽  
Single Frequency ◽  
Dual Frequency ◽  
Lever Arm ◽  
Rtk Gps ◽  
Camera Synchronization

In recent years, unmanned aerial vehicles (UAVs) have increasingly been used in various application areas, such as in the remote sensing or surveying. For these applications the UAV has to be equipped with a mapping sensor, which is mostly a camera. Furthermore, a georeferencing of the UAV platform and/or the acquired mapping data is required. The most efficient way to realize this georeferencing is the direct georeferencing, which is based on an onboard multi-sensor system. In recent decades, direct georeferencing systems have been researched and used extensively in airborne, ship and land vehicle applications. However, these systems cannot easily be adapted to UAV platforms, which is mainly due to weight and size limitations. <br><br> In this paper a direct georeferencing system for micro- and mini-sized UAVs is presented, which consists of a dual-frequency geodetic grade OEM GPS board, a low-cost single-frequency GPS chip, a tactical grade IMU and a magnetometer. To allow for cm-level position and sub-degree attitude accuracies, RTK GPS (real-time kinematic) and GPS attitude (GPS compass) determination algorithms are running on this system, as well as a GPS/IMU integration. <br><br> Beside the direct georeferencing, also the precise time synchronization of the camera, which acts as the main sensor for mobile mapping applications, and the calibration of the lever arm between the camera reference point and the direct georeferencing reference point are explained in this paper. Especially the high accurate time synchronization of the camera is very important, to still allow for high surveying accuracies, when the images are taken during the motion of the UAV. <br><br> Results of flight tests demonstrate that the developed system, the camera synchronization and the lever arm calibration make directly georeferenced UAV based single point measurements possible, which have cm-level accuracies on the ground.

Development of a field-of-view scanning system (FoV-SS): test results and lessons learned

2018 ◽  
Author(s):  
Miguel Ángel Esteves Pérez ◽  
Carlos Dominguez-Tagle ◽  
Olivier Grassin ◽  
Nauzet Vega Reyes ◽  
Manuel Collados Vera ◽  
...  
Keyword(s):  
Lessons Learned ◽  
Field Of View ◽  
Scanning System ◽  
Test Results

scholarly journals KOOLS–IFU: Kyoto Okayama Optical Low-dispersion Spectrograph with optical-fiber Integral Field Unit

2019 ◽  
Vol 71 (5) ◽  
Author(s):  
Kazuya Matsubayashi ◽  
Kouji Ohta ◽  
Fumihide Iwamuro ◽  
Ikuru Iwata ◽  
Eiji Kambe ◽  
...  
Keyword(s):  
Optical Fiber ◽  
Gamma Ray ◽  
Field Of View ◽  
Resolving Power ◽  
Optimal Conditions ◽  
Total Field ◽  
Fiber Array ◽  
Field Unit ◽  
Low Dispersion ◽  
Integral Field

Abstract Observations of transient objects, such as short gamma-ray bursts and electromagnetic counterparts of gravitational wave sources, require prompt spectroscopy. To carry out prompt spectroscopy, we have developed an optical-fiber integral field unit (IFU) and connected it with an existing optical spectrograph, KOOLS. KOOLS–IFU was mounted on the Okayama Astrophysical Observatory 188 cm telescope. The fiber core and cladding diameters of the fiber bundle are 100 μm and 125 μm, respectively, and 127 fibers are hexagonally close-packed in the sleeve of the two-dimensional fiber array. We conducted test observations to measure the KOOLS–IFU performance and obtained the following conclusions: (1) the spatial sampling is ${2{^{\prime\prime}_{.}}34}$$\, \pm \,$${0{^{\prime\prime}_{.}}05}$ per fiber, and the total field of view is ${30{^{\prime\prime}_{.}}4}$$\, \pm \,$${0{^{\prime\prime}_{.}}65}$ with 127 fibers; (2) the observable wavelength and the spectral resolving power of the grisms of KOOLS are 4030–7310 Å and 400–600, 5020–8830 Å and 600–900, 4160–6000 Å and 1000–1200, and 6150–7930 Å and 1800–2400, respectively; and (3) the estimated limiting magnitude is 18.2–18.7 AB mag during 30 min exposure under optimal conditions.

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