Error analysis and correction for extracting the forest height from airborne C-band interferometric SAR and national elevation datasets

The Interferometric Synthetic Aperture Radar (InSAR) signal is returned from the canopy of the obscuring trees instead of bare ground when land is covered by forests. Therefore, the difference between an InSAR elevation and a bare earth model might contain information on forest height. The objective of this paper was to investigate if the difference between an airborne C-band InSAR from the National Aeronautics and Space Administration (NASA)/Jet Propulsion Laboratory (JPL) and a bare earth model of 1/3 arcsecond National Elevation Datasets can be used for regional forest height estimation. The error sources of vertical offset, uncompensated roll angle, residual vertical bias, and scattering phase centre height conversion were analysed and corrected in this estimation. The results were validated by the least-square linear regression analysis between Light Detection and Ranging (LiDAR) and the estimated height at different forest stand sizes within different slope categories. In areas with slopes less than 5°, the correlation coefficients increased when forest stand sizes increased. In the area of slope ranging from 5 to 10°, a similar trend of increasing correlation coefficients with increasing stand size could also be observed, but with smaller corresponding correlation coefficients than those of slope 0–5°. In areas with slopes larger than 10°, the correlation coefficients were very poor. These results indicate the difference between airborne C-band InSAR and the accurate bare earth model has the potential for regional forest height estimation in flat areas with a minimum unit of 3750–5000 m². However, to accurately estimate forest height in a mountainous terrain a solution must be found to correct the significant amount of noise caused by the terrain in these areas.     

Estimating surface solar radiation over complex terrain using moderate‐resolution satellite sensor data

It is well known that taking into account the influence of complex terrain is essential when using high‐resolution satellite remotely sensed data to estimate surface net solar radiation. This paper investigates whether this is also the case when using moderate‐resolution satellite remotely sensed data, such as Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR). Firstly, topographic data from a gridded digital elevation model, field measurements from the Tibetan Plateau, and results from the atmospheric 6S model are used to estimate surface incoming solar radiation over complex terrain. The associated error caused by not taking into account terrain complexity is then calculated, and the relative radiation error is estimated by standardizing the error. The results show that the standard deviation of the relative radiation error depends on the solar zenith angle, standard deviation of the height, and resolution of the digital elevation model (or resolution of the satellite sensor data). A single regression equation describes the change in the standard deviation of the relative radiation error with solar zenith angle, standard deviation of height, and resolution of the digital elevation model. This demonstrates that it is necessary to consider terrain complexity when using moderate‐resolution remotely sensed data.     

Bowing with a trunk flexion of 90°: Perspectives on consumers and service personnel

In this study, we analyzed 100 questionnaire responses to determine consumer conceptions of service personnel bowing as a gesture of politeness. In addition, 12 female participants demonstrate five distinct degrees of bowing by bending their trunk 30°, 45°, 60°, and 90° from an upright position; their spinal curvature and trunk muscle activations were measured. The results showed that most respondents believed that bowing at 30° was the most satisfactory angle, followed by 45°. Bowing at 45° or 60° caused the survey respondents to feel honored, whereas bowing at 90° induced feelings of surprise and novelty; however, this angle produced the lowest proportion level of agreements on the items at ease, necessary, and appropriate among the 100 respondents. When the 12 participants bowed at an angle ≤60°, their spinal posture became increasingly kyphotic, and their muscle activations became more pronounced. Myoelectric silencing of the erector spinae was observed when the participants bowed at 90°, which can increase the risk of low back injury. These findings provide service industries with a reference for the design of service encounters.Relevance to industryBowing has traditionally signified politeness and respect in many countries. However, whether bowing at a greater trunk flexion actually satisfies customers remains unclear. Findings from this study clarify the customer perceptions and body loads of service personnel when bowing at various trunk positions. The extreme bowing postures (e.g., 90° trunk flexion) should be avoided.     

The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lifting

There are many work environments that require workers to perform manual materials handling tasks on ground surfaces that are not perfectly flat (e.g. in agriculture, construction, and maritime workplaces). These sloped ground surfaces may have an impact on the lifting strategy/technique employed by the lifter, which may, in turn, alter the biomechanical loading of the spine. Describing the changes in kinematics and kinetics of the torso is the first step in assessing the impact of these changes and is the focus of the current research. Subjects' whole-body motions were recorded as they lifted a 10 kg box while standing on two inclined surfaces (facing an upward slope: 10° and 20°), two declined surfaces (facing a downward slope: ? 10° and ? 20°), and a flat surface (0°) using three lifting techniques (leg lift, back lift and freestyle lift). These data were then used in a two-dimensional, five-segment dynamic biomechanical model (top-down) to evaluate the effect of these slopes on the net moment about the L5/S1 joint. The results of this study showed an interesting interaction effect wherein the net L5/S1 moment was relatively insensitive to changes in slope angle under the back lift condition, but showed a significant effect during the leg lift and freestyle lifting conditions. The results show that under the freestyle lifting condition the peak L5/S1 moment was significantly higher for the inclined surfaces as compared to the flat surfaces (6.8% greater) or declined surfaces (10.0% greater). Subsequent component analysis revealed that both trunk flexion angle and angular trunk acceleration were driving this response. Collectively, the results of this study indicate that ground slope angle does influence the lifting kinematics and kinetics and therefore needs to be considered when evaluating risk of low back injury in these working conditions.     

All terrain vehicle loss of control events in agriculture: Contribution of pitch,roll and velocity

All terrain vehicle (ATV) (i.e. quad bike) loss of control (LOC) events are a major cause of injury and death on New Zealand and Australian farms. ATV LOC history, work experience, anthropometric data and vehicle pitch, roll and velocity data were recorded from 30 farmers. The terrain induced 95th percentiles were forward pitch 27.8°, backward pitch 28.7° and 20.8° for left and right roll. Nineteen participants (mean 42.4 years) had experienced 53 LOC events and were on average 9.5 years younger than the 11 participants (mean 51.9 years) who had not previously experienced LOC. Peak pitch, roll and velocity were not associated with LOC; however, at peak left roll the non-LOC group had a pitch of 3.1° downhill, while the LOC group had a pitch of 2.1° uphill. Results indicate ATV LOC prevalence is considerably underestimated, while increased risk for LOC may be influenced by a combination of personal, mechanical or terrain factors. The ATV pitch, roll and slope traverse data may help in the better understanding of why LOC events occur, may help in the development of safety equipment such as a tilt warning device and will contribute to national safety guidelines.

Statement of Relevance: Approximately 80,000 ATVs are used in rural New Zealand and ATV accidents are the single most common cause of work-related fatalities, apart from road accidents. This fieldwork research provides pitch, roll and velocity data and considers how these data might contribute to risk of ATV accidents.     

High-resolution terrain map from multiple sensor data

The authors present 3-D vision techniques for incrementally building an accurate 3-D representation of rugged terrain using multiple sensors. They have developed the locus method to model the rugged terrain. The locus method exploits sensor geometry to efficiently build a terrain representation from multiple sensor data. The locus method is used to estimate the vehicle position in the digital elevation map (DEM) by matching a sequence of range images with the DEM. Experimental results from large-scale real and synthetic terrains demonstrate the feasibility and power of the 3-D mapping techniques for rugged terrain. In real world experiments, a composite terrain map was built by merging 125 real range images. Using synthetic range images, a composite map of 150 m was produced from 159 images. With the proposed system, mobile robots operating in rugged environments can build accurate terrain models from multiple sensor data     

An improved topographic mapping technique from airborne lidar: application in a forested hillside

We developed a robust method to reconstruct a digital terrain model (DTM) by classifying raw light detection and ranging (lidar) points into ground and non-ground points with the help of the Progressive Terrain Fragmentation (PTF) method. PTF applies iterative steps for searching terrain points by approximating terrain surfaces using the triangulated irregular network (TIN) model constructed from ground return points. Instead of using absolute slope or offset distance, PTF uses orthogonal distance and relative angle between a triangular plane and a node. Due to this characteristic, PTF was able to classify raw lidar points into ground and non-ground points on a heterogeneous steep forested area with a small number of parameters. We tested this approach by using a lidar data set covering a part of the Angelo Coast Range Reserve on the South Fork of the Eel River in Mendocino County, California, USA. We used systematically positioned 16 reference plots to determine the optimal parameter that can be used to separate ground and non-ground points from raw lidar point clouds. We tested at different admissible hillslope angles (15° to 20°), and the minimum total error (1.6%) was acquired at the angle value of 18°. Because classifying raw lidar points into ground and non-ground points is the basis for other types of analyses, we expect that our study will provide more accurate terrain approximation and contribute to improving the extraction of other forest biophysical parameters.     

Automatic targetless camera–LIDAR calibration by aligning edge with Gaussian mixture model

This paper presents a calibration algorithm that does not require an artificial target object to precisely estimate a rigid‐body transformation between a camera and a light detection and ranging (LIDAR) sensor. The proposed algorithm estimates calibration parameters by minimizing a cost function that evaluates the edge alignment between two sensor measurements. In particular, the proposed cost function is constructed using a projection model‐based many‐to‐many correspondence of the edges to fully exploit measurements with different densities (dense photometry and sparse geometry). The alignment of the many‐to‐many correspondence is represented using the Gaussian mixture model (GMM) framework. Here, each component of the GMM, including weight, displacement, and standard deviation, is derived to suitably capture the intensity, location, and influential range of the edge measurements, respectively. The derived cost function is optimized by the gradient descent method with an analytical derivative. A coarse‐to‐fine scheme is also applied by gradually decreasing the standard deviation of the GMM to enhance the robustness of the algorithm. Extensive indoor and outdoor experiments validate the claim that the proposed GMM strategy improves the performance of the proposed algorithm. The experimental results also show that the proposed algorithm outperforms previous methods in terms of precision and accuracy by providing calibration parameters of standard deviations less than 0.6° and 2.1 cm with a reprojection error of 1.78 for a 2.1‐megapixel image (2,048 × 1,024) in the best case.     

Wrist postures while keyboarding: effects of a negative slope keyboard system and full motion forearm supports

Abstract

Video-motion analysis was used to analyse hand/wrist posture for subjects typing at a 101-key QWERTY keyboard on a 68 cm high worksurface. Three conditions were tested: subjects typed at the keyboard without arm support, subjects typed with adjustable full motion forearm supports, and subjects typed with an adjustable negative slope keyboard support system. The average declination of the negative slope keyboard support chosen by subjects was 12° below horizontal, which flattened the angle of the key tops. Ulnar deviation was comparable in all conditions and averaged 13° for the right hand and 15° for the left hand. Full motion forearm supports did not significantly affect any postural measures. Dorsal wrist extension averaged 13° when typing with or without the full motion forearm supports, but this was reduced to an average — 1° with the use of the negative slope keyboard support system. Subjects chose to sit at a distance of 79 cm from the computer screen when using the negative slope keyboard system compared with 69 cm without this.     

消化道诊疗胶囊三维磁定位系统的误差修正

设计了基于三轴磁感传感器阵列的体内微型诊疗胶囊定位跟踪系统,分析了系统的主要误差来源,提出了对背景磁场干扰、传感器灵敏度差异、传感器位置偏差、三轴传感器模块的非理想正交等误差的补偿和修正方法,并进行了定位实验和轨迹跟踪实验以检验误差修正效果。实验结果表明:误差修正后系统的定位与定向精度得到显著提高,对于距离传感器阵列平面150 mm的φ8 mm×8 mm的圆柱形N35铷铁硼永磁体,平均定位与精度达到8mm以内,平均定向精度达到6°以内,并能够对沿模拟肠道运动的内置永磁体的电子胶囊进行轨迹跟踪。     

大视场数字式太阳敏感器设计

提出了一种新型的大视场数字式太阳敏感器设计方法,其光学系统由全景环形光学镜头和滤光膜组成.该敏感器具有视场大、结构简单及功耗低的特点.从工作原理出发,建立了该敏感器模型,并利用搭建的实验平台,对敏感器进行精度标定.设计中,采用非线性最小均方最优解来确定模型中的参数.对测量误差进行分析,消除系统误差后,敏感器的测量精度由...     

An estimation method for InSAR interferometric phase combined with image auto-coregistration

1 Introduction Synthetic aperture radar interferometry (InSAR) is an important remote sensing tech- nique to retrieve the terrain digital elevation model (DEM)[1,2]. Image coregistration and interferometric phase unwrapping are two key processing procedur…     

Incorporation of azimuthal control methods in the extraction of 3-dimensional topographic models from individual space-borne SAR scenes

Abstract

The radiometric variability of SAR images of rugged terrain is determined largely by surface orientation, specifically the range-directed component of terrain slope. This implies that although image shading information can be employed to derive elevation profiles for individual range lines, these profiles are decoupled due to the lack of azimuthal control. Two sources of azimuthal control are proposed which allow one to derive a 3-dimensional model of terrain for a SAR image swath. Range lines can be tied to an absolute coordinate grid through the use of an elevation transect or azimuthal control line (ACL). Slope integration away from the ACL will incur errors due to image speckle and radiometric calibration uncertainties. Periodic adjustment can be accomplished with the second source of control, a relative one, which employs lake levelling and the automated extraction and smoothing of valley floors. The above techniques have been utilized to derive terrain models from two Seasat subscenes. Over integration distances of 40 km, systematic and random components of error have been limited to 181 and 113 m, respectively. Although the derived DEMs are not of mapping quality they do provide useful, quantitative measures of the topographic shape of local scene features.     

The (in)accuracy of novice rover operators' perception of obstacle height from monoscopic images

Researchers have previously described a mobile robot, or rover, operator's difficulty in accurately perceiving the rover's tilt and roll, which can lead to rollover accidents. Safe mobile robot navigation and effective mission planning also require an operator to accurately interpret and understand the geometry and scale of features in the rover's environment. This work presents an experiment that measures an observer's ability to estimate height of distant (5-15 m) obstacles given an accurate local model (e.g., within 0-5 m of the rover), a panoramic image, and a physical mock-up of the local terrain. The experimental conditions were intended to represent a best-case scenario for a stopped rover equipped with short base-line stereoscopic cameras. The participants' task was to extrapolate the well-modeled local geometry to monoscopic images of the more distant terrain. The experiment compared two estimation techniques. With the first technique, each observer physically indicated his or her direct estimates of the obstacle distance and height. With the second estimation technique, which we call horizon analysis, the observer indicated the position of the top and bottom of each rock on an image and the height was calculated by measuring the visual angle between the theoretical horizon and the points indicated by the observer. The direct estimation technique overestimated the height of the rocks by an average of 190%; the horizon analysis technique overestimated by 80%. The results suggest that even when provided with a rich set of supplementary and context information, rover operators have significant difficulty in vertically perceiving the scale of distant terrain. The results also suggest that horizon analysis is a more accurate method for determining the height of distant rover navigation obstacles, when the local terrain is nearly level.     

Online turnover‐free control for a mobile agent with a terrain prediction sensor

This paper proposes a turnover‐free control method for a teleoperated mobile agent (or vehicle) moving through uneven terrain. The teleoperated agent is primarily driven by an operator at a remote site and is able to react autonomously when a possible turnover is predicted. In order to predict the turnover, a low‐cost terrain prediction sensor has been developed using a camera vision with a structured laser light. Since it is difficult for an operator to predict the reactive motion of the agent, a force reflection technique with a force feedback joystick is employed to intuitively recognize the inconsistency between the intended motion and the reactive motion of the agent. Finally, to verify the feasibility and effectiveness of the proposed method, experiments with the ROBHAZ‐DT (actual mobile agent) have been carried out. In the experiments, the operator could recognize the reactive motion of the agent for turnover prevention through force reflection while the agent was moving on slopped terrain. © 2006 Wiley Periodicals, Inc.     

Using NDVI to define thermal south in several mountainous landscapes of California

We combined normalized difference vegetation index (NDVI) and digital terrain analysis to detect thermal south (defined in this paper as the warmest slope azimuth, especially for plant growth) in three mountainous landscapes of California. Two methods, respectively, defined topography-controlled thermal south as corresponding to (1) the maximum NDVI contrast between opposite topographic aspects or (2) the maximum covariance between NDVI and deviated southness. Southness was obtained from aspect (slope azimuth in degrees) by taking its negative cosine value. A multi-scale approach using multi-seasonal NDVI images of the three study areas defined that thermal south would vary with seasons, spatial scales, and study areas, but it deviated from 0° to 180° azimuth line towards southwest in all cases. A deviation angle should thereby be applied when aspect is used as a topographic proxy indicating local thermal conditions. However, the angle must be defined in a way specific to the landscape, scale, and season that are under investigation, hence requiring rapid, easy-to-use tools. The two methods, suggested in this paper, reported comparable thermal south and, together with resultant findings, they may contribute to the study of mountain landscapes, since direct meteorological observations are usually sparse or non-existent in mountains.     

超声速气流中复合材料壁板的动力学分析及其控制

超声速飞行器外表具有大量的蒙皮壁板结构,其在巡航过程中会受到气动、热、声及机械等载荷的联合作用.本文针对超声速气流中的复合材料壁板结构,基于一阶剪切变形理论(First-Order Shear Deformation Theory,FSDT)和超声速活塞理论,推导得到了复合材料壁板的气热弹动力学的能量泛函,并运用Hamilton原理变分求得系统的控制方程,利用牛顿迭代法结合Newmark法,求解获得了壁板的临界颤振动压和时域动力学响应.通过变参数计算,分析了不同参数对于壁板动力学响应的影响.最后,应用非线性能量阱(Nonlinear Energy Sink,NES)对复合材料壁板的动力学响应进行颤振控制,结果表明,NES可以有效降低壁板的颤振极限环振幅,从而极大提高超声速飞行器的可靠性和寿命.     

Mapping simulated error due to terrain slope in airborne lidar observations

Quantification of geo-location error in light detection and ranging (lidar) observations is typically limited to empirical assessments, commonly quantified as the fundamental vertical accuracy (FVA). Methodological recommendations indicate that validation observations used for quantifying the FVA should not be collected in sloped terrain; however, terrain slope has been shown to contribute to the lidar error budget. Therefore, users of lidar information generally do not have adequate information to characterize error in sloped conditions. This study proposes a novel geometric terrain-based error propagation algorithm for simulating error bounds of individual lidar observations in the presence of terrain slope. A steep, glacierized, alpine test site in the Canadian Rockies was used to evaluate the algorithm. Error simulations were modelled from the terrain-based error propagation algorithm as well as a pre-existing sensor hardware error propagation algorithm and validated with high-accuracy GPS observations. Simulated versus observed errors showed that terrain-based error simulations provided a reasonable ‘worst-case scenario’ simulation of potential error and were superior to hardware-only simulated errors. Results were separated into three individual flight lines, and terrain-based error simulations were greater than the observed errors in 82%, 89%, and 100% of the tested points in each respective flight line, or 90%, overall. This contrasted hardware-only error simulations, which were greater than observed errors in 32%, 42%, and 84% of tested points in each respective flight line, or 50% overall. This work provides a comprehensive understanding of the distribution of errors within lidar point clouds over complex terrain types and provides a new methodology for propagating lidar observational errors into derived products.     

基于相对特征的越野地形可通行性分析

自主地面车在越野环境下导航面临最困难的问题之一是对地形的理解，分析感知到的越野地形，作适合于自主车导航的可通行性分析。本文提出了越野高程地形的相对不变性概念，并利用这种性质提取出在一定尺度范围内地形具有的相对不变特征，如地形坡度、起伏度和粗糙度，最后基于模糊规则组合各特征对地形的可通行性进行评估。自主车越野导航实验表明，本文算法稳定有效，能满足自主地面车越野导航的需要。     

The Impact of Function Location on Typing and Pointing Tasks With an Intraoral Tongue–Computer Interface

Intraoral target (typing) and on-screen target (pointing/tracking) selection tasks were performed by 10 participants during 3 consecutive day sessions. Tasks were performed using 2 different intraoral sensor layouts. Reduction of undesired sensor activations while speaking as well as the influence of intraoral temperature variation on the signals of the intraoral interface was investigated. Results showed that intraoral target selection tasks were performed better when the respective sensor was located in the anterior area of the palate, reaching 78 and 16 activations per minute for repetitive and “unordered” sequences, respectively. Virtual target pointing and tracking tasks, of circles of 50, 70, and 100 pixels diameter, showed no significant difference in performance, reaching average pointing throughputs of 0.62 to 0.72 bits per second and relative time on target of 34% to 60%. Speaking tasks caused an average of 10 to 31 involuntary activations per minute in the anterior part of the palate. Intraoral temperature variation between 11.87 °C and 51.37 °C affected the sensor signal baseline in a range from –25.34% to 48.31%. Results from this study provide key design considerations to further increase the efficiency of tongue–computer interfaces for individuals with upper-limb mobility impairments.