Accuracy Of Direct Measurement Research Articles

An Improved Dust-Concentration Measurement Algorithm Based on Multifeature Fusion of β-Ray Intensity Fluctuations

Although $\beta $ -ray measurements remain one of the main methods for determining the concentration of dust in mines, the accuracy of direct measurements is impacted by radiation-intensity fluctuations across the probe beam. We collected coal-dust samples on membrane filters and compared the dust-concentration levels from a basic algorithm for determining the concentration by $\beta $ -ray absorption through the membranes with the levels calculated using a newly developed algorithm. The two algorithms both used standardized weights of coal deposited on the membranes but differed in the particular statistical variables used to describe the $\beta $ -ray characteristics. Our analysis revealed how $\beta $ -ray intensity fluctuations affected measurement accuracy and precision, thereby highlighting the limitations of the basic algorithm. We evaluated the standard deviation and envelope mean functions that characterized the fluctuations in the probe-beam flux, and we then used those statistics to derive new algorithms for better concentration accuracy. We employed a data fusion technique to establish a new algorithm. The new algorithm was tested experimentally and was shown to reduce the influence of the intensity fluctuations on the measurement of coal-dust concentrations, enhancing both the accuracy and reliability of the readings.

Autonomous Collection of Forest Field Reference—The Outlook and a First Step with UAV Laser Scanning

A compact solution for the accurate and automated collection of field data in forests has long been anticipated, and tremendous efforts have been made by applying various remote sensing technologies. The employment of advanced techniques, such as the smartphone-based relascope, terrestrial and mobile photogrammetry, and laser scanning, have led to steady progress, thus steering their applications to a practical stage. However, all recent strategies require human operation for data acquisition, either to place the instrument on site (e.g., terrestrial laser scanning, TLS) or to carry the instrument by an operator (e.g., personal laser scanning, PLS), which remained laborious and expensive. In this paper, a new concept of autonomous forest field investigation is proposed, which includes data collection above and inside the forest canopy by integrating an unmanned aircraft vehicle (UAV) with autonomous driving. As a first step towards realizing this concept, the feasibility of automated tree-level field measurements from a mini-UAV laser scanning system is evaluated. A “low-cost” Velodyne Puck LITE laser scanner is applied for the test. It is revealed that, with the above canopy flight data, the detection rate was 100% for isolated and dominant trees. The accuracy of direct measurements on the diameter at breast height (DBH) from the point cloud is between 5.5 and 6.8 cm due to the system and the methodological error propagation. The estimation of DBH from point cloud metrics, on the other hand, showed an accuracy of 2.6 cm, which is comparable to the accuracies obtained with terrestrial surveys using mobile laser scanning (MLS), TLS or photogrammetric point clouds. The estimation of basal area, stem volume and biomass of individual trees could be obtained with less than 20% RMSE, which is adequate for field reference measurements at tree level. Such results indicate that the concept of UAV laser scanning-based automated tree-level field reference collection can be feasible, even though the whole topic requires further research.

Ultrasonic Direction Measurement Method Using Sensitivity Compensated Transmitting Signal and Pulse Compression

We have studied high resolution pulse compression technique for ultrasonic pulse-echo measurement. To acquire broader and flatter spectrum, a Sensitivity Compensate Transmitting (SCT) signal was proposed. The SCT signal is calculated from inversed filtering of received signal. Here, two types SCT signal are proposed. As a Sensitivity Compensated AM (SCAM) signal, an amplitude modulated chirp wave is proposed. Furthermore, for higher Signal to Noise Ratio (SNR), a non-linear FM signal is proposed as a Sensitivity Compensate FM (SCFM) signal. In this paper, effectiveness of the SCT signal on 2-D direction measurement is discussed. By using the SCT signal, the time resolution of compressed pulse is improved, and accuracies of direction measurement using the SCT signal are improved than that of using the chirp wave. Furthermore, by using the SCFM signal, accuracy of direction measurement is improved than that of using the SCAM signal when the target is located at the position where the SNR of received signal is lower.

A simple and accurate method for detecting cube corner rotations

Cube corners are used widely in position detecting devices. A cube corner is attached to an object of interest. Then the position of the object is determined as the distance and two angles of direction to the cube corner. Recent developments make it possible to use a cube corner to detect the orientation of an object as well. However orientation cannot be measured directly, instead it should be recovered from other data. The paper introduces a method of calculating the orientation of a cube corner and shows that the method has an accuracy restricted by the accuracy of direct measurements only. Hence it detects orientation angles of a cube corner up to arc seconds.

Generalization of the problem of determining the accuracy of direct measurements for achievement of given accuracies in indirect measurements

Using a general statement of the problem, we consider determination of the accuracy required in direct measurements to achieve a given accuracy of indirect measurements related to the direct measurements by some known relationship. A solution to the problem is stated as a theorem and corollaries. Examples are presented to illustrate how the solution obtained here can be applied in concrete cases.