More Like this

1. Simple Camera-to-2D-LiDAR Calibration Method for General Use

   Palmer, A. ; Peterson, C. ; Blankenburg, J. ; Feil-Seifer, D. ; Nicolescu, M. ( October 2020 , ISVC'20: 15TH INTERNATIONAL SYMPOSIUM ON VISUAL COMPUTING)

   null (Ed.)

   As systems that utilize computer vision move into the public domain, methods of calibration need to become easier to use. Though multi-plane LiDAR systems have proven to be useful for vehicles and large robotic platforms, many smaller platforms and low cost solutions still require 2D LiDAR combined with RGB cameras. Current methods of calibrating these sensors make assumptions about camera and laser placement and/or require complex calibration routines. In this paper we propose a new method of feature correspondence in the two sensors and an optimization method capable of calibration target with unknown lengths in its geometry. Our system is designed with an inexperienced layperson as the intended user, which has lead us to remove as many assumptions about both the target and laser as possible. We show that our system is capable of calibrating the 2-sensor system from a single sample in configurations other methods are unable to handle. 

   more » « less
2. Autonomous in situ calibration of ion‐sensitive field effect transistor pH sensors

   https://doi.org/10.1002/lom3.10410  

   Bresnahan, Philip J. ; Takeshita, Yuichiro ; Wirth, Taylor ; Martz, Todd R. ; Cyronak, Tyler ; Albright, Rebecca ; Wolfe, Kennedy ; Warren, Joseph K. ; Mertz, Keaton ( January 2021 , Limnology and Oceanography: Methods)

   Ion‐sensitive field effect transistor‐based pH sensors have been shown to perform well in high frequency and long‐term ocean sampling regimes. The Honeywell Durafet is widely used due to its stability, fast response, and characterization over a large range of oceanic conditions. However, potentiometric pH monitoring is inherently complicated by the fact that the sensors require careful calibration. Offsets in calibration coefficients have been observed when comparing laboratory to field‐based calibrations and prior work has led to the recommendation that an in situ calibration be performed based on comparison to discrete samples. Here, we describe our work toward a self‐calibration apparatus integrated into a SeapHOx pH, dissolved oxygen, and CTD sensor package. This Self‐Calibrating SeapHOx is capable of autonomously recording calibration values from a high quality, traceable, primary reference standard: equimolar tris buffer. The Self‐Calibrating SeapHOx's functionality was demonstrated in a 6‐d test in a seawater tank at Scripps Institution of Oceanography (La Jolla, California, U.S.A.) and was successfully deployed for 2 weeks on a shallow, coral reef flat (Lizard Island, Australia). During the latter deployment, the tris‐based self‐calibration using 15 on‐board samples exhibited superior reproducibility to the standard spectrophotometric pH‐based calibration using > 100 discrete samples. Standard deviations of calibration pH using tris ranged from 0.002 to 0.005 whereas they ranged from 0.006 to 0.009 for the standard spectrophotometric pH‐based method; the two independent calibration methods resulted in a mean pH difference of 0.008. We anticipate that the Self‐Calibrating SeapHOx will be capable of autonomously providing climate quality pH data, directly linked to a primary seawater pH standard, and with improvements over standard calibration techniques.

    

   more » « less
3. Testing and evaluation of a new airborne system for continuous N₂O, CO₂, CO, and H₂O measurements: the Frequent Calibration High-performance Airborne Observation System (FCHAOS)

   https://doi.org/10.5194/amt-11-6059-2018  

   Gvakharia, Alexander ; Kort, Eric A. ; Smith, Mackenzie L. ; Conley, Stephen ( January 2018 , Atmospheric Measurement Techniques)

   Abstract. We present the development and assessment of a new flight system that uses acommercially available continuous-wave, tunable infrared laser directabsorption spectrometer to measure N₂O, CO₂, CO, andH₂O. When the commercial system is operated in an off-the-shelfmanner, we find a clear cabin pressure–altitude dependency forN₂O, CO₂, and CO. The characteristics of this artifactmake it difficult to reconcile with conventional calibration methods. Wepresent a novel procedure that extends upon traditional calibrationapproaches in a high-flow system with high-frequency, short-duration samplingof a known calibration gas of near-ambient concentration. This approachcorrects for cabin pressure dependency as well as other sources of drift inthe analyzer while maintaining a ∼90% duty cycle for 1Hz sampling.Assessment and validation of the flight system with both extensive in-flightcalibrations and comparisons with other flight-proven sensors demonstrate thevalidity of this method. In-flight 1σ precision is estimated at0.05ppb, 0.10ppm, 1.00ppb, and 10ppm for N₂O,CO₂, CO, and H₂O respectively, and traceability to WorldMeteorological Organization (WMO) standards (1σ) is 0.28ppb,0.33ppm, and 1.92ppb for N₂O, CO₂, and CO. We showthe system is capable of precise, accurate 1Hz airborne observations ofN₂O, CO₂, CO, and H₂O and highlight flightdata, illustrating the value of this analyzer for studying N₂Oemissions on ∼100km spatial scales.

    

   more » « less
4. Effects of model incompleteness on the drift-scan calibration of radio telescopes

   https://doi.org/10.1093/mnras/stab2072  

   Gehlot, Bharat K ; Jacobs, Daniel C ; Bowman, Judd D ; Mahesh, Nivedita ; Murray, Steven G ; Kolopanis, Matthew ; Beardsley, Adam P ; Abdurashidova, Zara ; Aguirre, James E ; Alexander, Paul ; et al ( August 2021 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Precision calibration poses challenges to experiments probing the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and Epoch of Reionization (z ∼ 30–6). In both interferometric and global signal experiments, systematic calibration is the leading source of error. Though many aspects of calibration have been studied, the overlap between the two types of instruments has received less attention. We investigate the sky based calibration of total power measurements with a HERA dish and an EDGES-style antenna to understand the role of autocorrelations in the calibration of an interferometer and the role of sky in calibrating a total power instrument. Using simulations we study various scenarios such as time variable gain, incomplete sky calibration model, and primary beam model. We find that temporal gain drifts, sky model incompleteness, and beam inaccuracies cause biases in the receiver gain amplitude and the receiver temperature estimates. In some cases, these biases mix spectral structure between beam and sky resulting in spectrally variable gain errors. Applying the calibration method to the HERA and EDGES data, we find good agreement with calibration via the more standard methods. Although instrumental gains are consistent with beam and sky errors similar in scale to those simulated, the receiver temperatures show significant deviations from expected values. While we show that it is possible to partially mitigate biases due to model inaccuracies by incorporating a time-dependent gain model in calibration, the resulting errors on calibration products are larger and more correlated. Completely addressing these biases will require more accurate sky and primary beam models. 

   more » « less
5. Development of a Peripheral-Central Vision System for Small UAS Tracking

   https://doi.org/10.2514/6.2019-2074  

   Kang, Changkoo ; Chaudhry, Haseeb ; Woolsey, Craig A. ; Kochersberger, Kevin B. ( January 2019 , AIAA SciTech)

   With the rapid proliferation of small unmanned aircraft systems (UAS), the risk of mid-air collisions is growing, as is the risk associated with the malicious use of these systems. Airborne Detect-and-Avoid (ABDAA) and counter-UAS technologies have similar sensing requirements to detect and track airborne threats, albeit for different purposes: to avoid a collision or to neutralize a threat, respectively. These systems typically include a variety of sensors, such as electro-optical or infrared (EO/IR) cameras, RADAR, or LiDAR, and they fuse the data from these sensors to detect and track a given threat and to predict its trajectory. Camera imagery can be an effective method for detection as well as for pose estimation and threat classification, though a single camera cannot resolve range to a threat without additional information, such as knowledge of the threat geometry. To support ABDAA and counter-UAS applications, we consider a merger of two image-based sensing methods that mimic human vision: (1) a "peripheral vision" camera (i.e., with a fisheye lens) to provide a large field-of-view and (2) a "central vision" camera (i.e., with a perspective lens) to provide high resolution imagery of a specific target. Beyond the complementary ability of the two cameras to support detection and classification, the pair form a heterogeneous stereo vision system that can support range resolution. This paper describes the initial development and testing of a peripheral-central vision system to detect, localize, and classify an airborne threat and finally to predict its path using knowledge of the threat class. 

   more » « less