Whole body vibration exposure patterns in Canadian prairie farmers

Abstract

Whole body vibration is a significant physical risk factor associated with low back pain. This study assessed farmers’ exposure to whole body vibration on the Canadian prairies according to ISO 2631-1. Eighty-seven vibration measurements were collected with a triaxial accelerometer embedded in a rubber seat pad at the operator-seat interface of agricultural machinery, including tractors, combines, pickup trucks, grain trucks, sprayers, swathers, all-terrain vehicles, and skid steers. Whole body vibration was highest in the vertical axis, with a mean (range) frequency-weighted root mean squared acceleration of 0.43 m/s² (0.19?1.06 m/s²). Mean crest factors exceeded 9 in all 3 axes, indicating high mechanical shock content. The vertical axis vibration dose value was 7.55 m/s^1.75 (2.18?37.59 m/s^1.75), with 41.4% of measurements within or above the health guidance caution zone. These high exposures in addition to an ageing agricultural workforce may increase health risks even further, particularly for the low back.

Practitioner Summary: Agricultural workers are frequently exposed to whole body vibration while operating farm equipment, presenting a substantial risk to musculoskeletal health including the low back. Assessing vibration exposure is critical in promoting a safe occupational environment, and may inform interventions to reduce farmer’s exposure to vibration.     

Six-degree-of-freedom whole-body vibration exposure levels during routine skidder operations

This research focuses on quantifying six-degree-of-freedom (6-DOF) whole-body vibration (WBV) exposure levels that occur in Northern Ontario skidders during routine field operating tasks. 6-DOF vibration running root-mean-square (RMS) acceleration levels at the operator/seat interface were determined for eight skidders while driving loaded, driving unloaded, picking up a load, dropping off a load and ploughing logs under field operating conditions. The acceleration data were weighted in accordance with ISO 2631–1:1997 and evaluated for both health and comfort outcomes. The mean running RMS weighted translational and rotational accelerations all exceeded 0.36 m/s² and 0.14 rad/s². The greatest average accelerations occurred while driving unloaded with this condition displaying translational vibration total values (VTV) that exceeded the upper limit of the ISO 2631–1:1997 health caution zone within an average of 2.3 h. Utilizing 6-DOF VTV, virtually all operating conditions would be designated as uncomfortable.

Statement of Relevance: This study provides one of the most comprehensive reports on vibration exposures in seated vehicle operators. The results are geared towards ergonomists with discussions on health effects and measurement concerns, while providing the raw vibration exposure data that will be useful to vehicle, component and vibration sensor designers.     

Vibration and comfort HI. Translational vibration of the feet and back

The effects on discomfort of the frequency and direction of the translational vibration of a footrest and flat firm backrest have been studied in two experiments. At frequencies in the range 2.5-63 Hz, the first experiment determined the levels of fore-and-aft, lateral and vertical vibration of the feet of seated subjects which caused them discomfort equivalent to that from 0.8 m/s² r.m.s. 10 Hz vertical vibration of a firm flat seat. The levels of fore-and-aft, lateral and vertical vibration at the back of a seat which were equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined in the second experiment. The vibration of the feet or back occurred without simultaneous vibration at the seat.

Individual and group equivalent comfort contours are presented. It is concluded that the data provide a useful initial indication of the relative contribution of foot and back vibration to discomfort. Equivalent comfort contours for foot vibration were similar for all three directions of vibration. The contours for vibration of the back show a high sensitivity to fore-and-aft vibration. The results obtained from two additional studies show that vibration from a backrest and other variations in seating conditions can influence subject comfort.     

Bedside safety rails: assessment of strength requirements and the appropriateness of current designs

This second paper in a series of studies of the discomfort produced by multi-axis vibration is concerned with rotational seat vibration. The effects of level, frequency and direction of the roll, pitch and yaw vibration of a firm flat seat have been studied in two experiments. At octave centre frequencies in the range 1-31.5 Hz the first experiment determined the levels of roll, pitch and yaw seat vibration which caused discomfort equivalent to 0-5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8 m/s² r.m.s. 10 Hz vertical seat vibration were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 31.5 Hz. In all cases the axis of rotation passed through the centre of the seat surface. There was no vibration of the feet and no backrest.

It was concluded that the shape of equivalent comfort contours need not normally depend on vibration, level. Both individual and group equivalent comfort contours are presented. Although there were significant correlations between subject size and subject relative discomfort it is not thought that these correlations have much practical application. In all three axes the median contours of vibration acceleration increase in proportion to vibration frequency. Sensitivity is greatest for roll vibration and least for yaw vibration of the seat.     

The whole-body vibration in operation of wheeled and tracked harvester IN PINUS thinning

Technological advances available in wood harvesting machines have provided productivity improvements and more comfort in forestry operations. However, operators may be exposed to whole-body vibration which can lead to a wide variety of health disorders and industry losses. This research aimed to evaluate the exposure of workers to whole-body vibration in thinning harvesting operations comparing two models of harvesters (tracked and wheeled) working in Pinus taeda stands submitted to the first commercial thinning. Whole-body vibration was determined by the three orthogonal axes (X, Y, and Z) using a 3-Axis integrator vibration meter, and the data were analyzed according to the criteria established by the ISO 2631–1:1997 and the European Directive, 2002/44/EC, concerning the resulting acceleration from normalized exposure A (8) and value of the resulting vibration dose value (VDV). The acceleration and vibration levels obtained by the tracked harvester presented mean values of A (8) of 0.6 m/s² and VDV 11.2 m/s^1.75, while by the wheeled harvester, mean values were A (8) of 0.4 m/s² and VDV 9.3 m/s^1.75, respectively. It was possible to verify the expressive vibration from the tracked harvester analysis, the operators were exposed to the whole-body vibration above the limits recommended by the regulating norms.     

Vibration and comfort I. Translational seat vibration

A series of studies of discomfort caused by multi-axis vibration at the seat, feet and back of seated persons is described. This first paper reports on studies with translational seat vibration. Two experiments concerned with the effects of level, frequency and direction of the translational vibration of a firm flat seat are reported.

At octave centre frequencies from 1 to 63 Hz the first experiment determined the levels of fore-and-aft, lateral and vertical seat vibration which caused discomfort equivalent to 0.5 and l.25m/s²r.m.s. 10 Hz vertical seat vibration. In the second experiment, comfort contours equivalent to 0.8m/s²r.m.s. 10 Hz vertical seat vibration and subject transmissibilities were determined from 18 males and 18 females at preferred third-octave centre frequencies from 1 to 100 Hz. In both studies the feet of subjects were not vibrated and there was no backrest.

It was concluded that the shapes of equivalent comfort contours need not normally depend on vibration level. The forms of both individual and group equivalent comfort contours and seat-to-head transmissibilities are presented. Significant correlations were found between subject characteristics (size and transmissibility) and subject relative discomfort. The males and females produced similar equivalent comfort contours.

Information on the computerized application of the method of constant stimuli which was developed for the series of experiments is presented together with a consideration of alternative methods of determining the central tendency of the data. A method of assessing the effect of vibrator distortion on judgements of equivalent discomfort is also defined.     

Inter-comparison of wind profiles in the tropical boundary layer remotely sensed from GPS radiosonde and Doppler wind lidar

Winds play a very important role in the dynamics of the lower atmosphere, and there is a need to obtain vertical distribution of winds at high spatio-temporal resolution for various observational and modelling applications. Profiles of wind speed and direction obtained at two tropical Indian stations using a Doppler wind lidar during the Indian southwest monsoon season were inter-compared with those obtained simultaneously from GPS upper-air sounding (radiosonde). Mean wind speeds at Mahbubnagar (16.73° N, 77.98° E, 445 m above mean sea level) compare well in magnitude for the entire height range from 100 m to 2000 m. The mean difference in wind speed between the two techniques ranged from ?0.81 m s^?1 to +0.41 m s^?1, and the standard deviation of wind speed differences ranged between 1.03 m s^?1 and 1.95 m s^?1. Wind direction by both techniques compared well up to about 1200 m height and then deviated slightly from each other at heights above, with a standard deviation in difference of 19°–48°. At Pune (18^○32′ N, 73^○51′ E, 559 m above mean sea level), wind speed by both techniques matched well throughout the altitude range, but with a constant difference of about 1 m s^?1. The root mean square deviation in wind speed ranged from 1.0 to 1.6 m s^?1 and that in wind direction from 20° to 45°. The bias and spread in both wind speed and direction for the two stations were computed and are discussed. The study shows that the inter-comparison of wind profiles obtained by the two independent techniques is very good under conditions of low wind speeds, and they show larger deviation when wind speeds are large, probably due the drift of the radiosonde balloon away from the location.     

Power hand tool vibration effects on grip exertions

Operation of vibrating power hand tools can result in excessive grip force, which may increase the risk of cumulative trauma disorders in the upper extremities. An experiment was performed to study grip force exerted by 14 subjects operating a simulated hand tool vibrating at 9.8 m/s² and 49 m/s² acceleration magnitudes, at 40 Hz and 160 Hz frequencies, with vibration delivered in three orthogonal directions, and with 1.5kg and 3.0kg load weights. Average grip force increased from 25.3 N without vibration to 32.1 N (27%) for vibration at 40 Hz, and to 27.1N (7%) for vibration at 160 Hz. Average grip force also increased from 27.4 N at 9.8 m/s² acceleration to 31.8 N (16%) at 49m/s². Significant interactions between acceleration x frequency, and frequency x direction were also found. The largest average grip force increase was from 25.3N without vibration to 35.8N (42%) for 40 Hz and 49 m/s² vibration. The magnitude of this increase was of the same order as for a two-fold increase in load weight, where average grip force increased from 22.5N to 35.0N (56%). A second experiment studied hand flexor and extensor muscle responses using electromyography for five subjects holding a handle vibrating at 8 m/s² using ISO weighted acceleration, with frequencies of 20 Hz, 40 Hz, 80 Hz and 160 Hz, and grip forces of 5%, 10% and 15% of maximum voluntary contraction. Muscle responses were greatest at frequencies where grip force was affected, indicating that the tonic vibration reflex was the likely cause of increased grip exertions.     

The design and development of suspended handles for reducing hand-arm vibration in petrol driven grass trimmer

The portable petrol driven grass trimmer is identified as a type of machine whose operator can be subjected to large magnitude of hand-arm vibration. These vibrations can cause complex vascular, neurological and musculoskeletal disorder, collectively named as hand-arm vibration syndrome. The vibration total level on the handle of grass trimmer of 11.30 m/s² was measured, and it has reached the exposure limit value of 5.0 m/s² for daily vibration exposure A(8). New suspended handles were designed to reduce the vibration level. Three different prototype handles with rubber mounts were designed. Handles were made of different materials, and the distance of rubber mounts were varied. From the study, it was observed that not all the handles with rubber mounts were effective in reducing hand-arm vibration. The reduction of vibration depended on the handle material and distance installed between rubber mount and vibration transmissibility of handle-isolation system. Subjective ratings of perception of vibration were measured, and the results indicated that operators were not fully aware of the level of vibration. A prototype handle that is made of heavier material results in the lowest hand-arm vibration of 2.69 m/s². The new handle has significantly reduced the vibration total value by 76% compare with the existing commercial handle.

Relevance to industry

Large numbers of workers are employed to perform grass trimming job in many developing countries. This paper presents the effect of handle types (commercial and prototype) on the commonly used grass trimmer.     

A cohort study of sciatic pain and measures of internal spinal load in professional drivers

In a prospective cohort study of 537 male professional drivers, the occurrence of sciatic pain showed stronger associations with measures of internal lumbar load expressed in terms of daily compressive dose, S_ed (MPa), and risk factor, R (non-dimensional), according to ISO/WD 2631-5 (2013), than with measures of daily vibration exposure calculated as either 8-h energy-equivalent frequency-weighted acceleration (ms^? 2 r.m.s.) or vibration dose value (ms^? 1.75) according to the EU Directive on mechanical vibration (2002). Herniated lumbar disc, previous lumbar trauma and physical work load were also powerful predictors of the occurrence of sciatic pain over time. Psychosocial work environment was poorly associated with sciatic pain. The boundary values of risk factor (R) for low and high probabilities of adverse health effects on the lumbar spine, as proposed by international standard ISO/WD 2631-5 (2013), tend to underestimate the health risk in professional drivers.     

Lidar profiling of aerosol scavenging parameters at a tropical station,Pune, India

In this study, we deal with observations of aerosol column content (height integration of vertical distribution of aerosol number density) that have been carried out using an Ar⁺ lidar for three different measurement cycles (each cycle consisting of three experimental days associated with non-rain, rain, and non-rain, respectively) of weekly spaced observations for pre-monsoon (March/April 1994), monsoon (September 1991), and post-monsoon (October 1998). Based on these observed profiles of aerosol number concentration on rainy days with respect to those on non-rainy days, vertical distributions of scavenging collection efficiencies (SCEs) are computed and discussed in this article. The SCE is found to decrease from 0.3 to 0.01 between the heights, 100 and 800 m for thunderstorm rain in April 1994, and during monsoon, it increases from 0.1 to 0.7. In the October 1998 episode, SCE was found to increase initially from 0.35 to 0.75 for heights between 40 and 200 m and thereafter decrease to 0.35 in the height interval of 200–800 m. For the rainfall intensity increase from 1 to 10 mm hour^?1, the corresponding scavenging coefficient (SC) for atmospheric layer 50–100 m varies from 4 × 10^?6 to 4 × 10^?5 s^?1 for thunderstorm in April 1994 and between 5 × 10^?6 and 5 × 10^?5 s^?1 in October 1998, respectively. During monsoon, these values vary from 3 × 10^?5 to 5 × 10^?4 s^?1. They lie in the range of those observed in the earlier field studies. The results are found useful to establish links between aerosols and cloud properties, and the influence of such interactions on weather and climate.     

A new wind retrieval algorithm for Jason-1 at high wind speeds

The altimeter wind speed algorithm at high wind speeds remains unsolved because of lack of observed data. In this study data at high wind speeds were generated using Yin's typhoon model, which consists of the Rankine vortex model and the angular momentum model with typhoon parameters, provided by the Joint Typhoon Warning Centre (JTWC). The accuracy of Yin's typhoon model can be validated by comparing it with recorded data from a weather station. By comparing the normalized radar backscatter cross‐section (NRCS) detected by the Jason‐1 altimeter with wind speed data inferred by Yin's typhoon model, an empirical algorithm valid for a range of wind speeds between 10 and 40 m s^–1 is developed and proposed. The proposed algorithm is compared with the Jason‐1 operational algorithm and Young's altimeter wind retrieval algorithm. The study shows that, for the proposed algorithm and the operational algorithm for Jason‐1, the root mean square (RMS) errors are 3.38 and 3.60 m s^–1, respectively, and the average relative errors are 18% and 19%, respectively, for wind speeds less than 27 m s^–1. Hence, the proposed algorithm is in agreement with the operational algorithm for the Jason‐1 altimeter for wind speeds in the range 10–27 m s^–1. However, the Jason‐1 operational algorithm is inaccurate for wind speeds above 27 m s^–1 because the wind speeds used in the algorithm training process came from scatterometer wind products, and are significantly lower than those in strong wind and heavy rain conditions. Comparison of the proposed algorithm and Young's algorithm shows that the RMS errors are 6.27 and 15.18 m s^–1, respectively, and the average relative errors are 16% and 59%, respectively, for wind speeds greater than 20 m s^–1. The Holland typhoon model cannot accurately determine the outer wind field of typhoons since it extends cyclonic wind speeds to infinity. Young's altimeter wind retrieval algorithm depends on the Holland typhoon model, and the latter results in some errors. Compared with Young's altimeter wind retrieval algorithm, the proposed algorithm retrieves wind speeds with better accuracy. Therefore, the proposed algorithm, suitable for retrieving sea surface wind speeds in typhoons and other strong wind conditions, can be considered as supplementary to the Jason‐1 operational algorithm.     

The effects of horizontal load speed and lifting frequency on lifting technique and biomechanics

Lifting loads that have a horizontal velocity (e.g. lifting from a conveyor) is often seen in industry and it was hypothesised that the inertial characteristics of these loads may influence lifting technique and low back stress. Seventeen male participants were asked to perform lifting tasks under conditions of four horizontal load speeds (0 m/s, 0.7 m/s, 1.3 m/s and 2.4 m/s) and two lifting frequencies (10 and 20 lifts/min) while trunk motions and trunk muscle activation levels were monitored. Results revealed that increasing horizontal load speed from 0 m/s to 2.4 m/s resulted in an increase in peak sagittal angle (73° vs. 81°) but lower levels of peak sagittal plane angular acceleration (480°/s² vs. 4°/s²) and peak transverse plane angular acceleration (200°/s per s vs. 140°/s per s) and a consistent increase in trunk muscle co-activation. Participants used the inertia of the load to reduce the peak dynamics of the lifting motion at a cost of increased trunk flexion and higher muscle activity.

Statement of Relevance: Conveyors are ubiquitous in industry and understanding the effects of horizontal load speed on the lifting motions performed by workers lifting items from these conveyors may provide some insight into low back injury risk posed by these tasks.     

Experimental Investigation To Study the Influence of Handle Diameter on Low‐Frequency,Hand–Arm Vertical Vibration

Handle vibration from equipment or machines influences musculoskeletal activity as well as comfort in handling the same. New technology can be worse than no technology if it was not developed correctly as ergonomic research has clearly demonstrated the relationship between injury risk and poorly designed hand tools. Clinical and epidemiological studies have shown that operators of handheld power tools are prone to develop various vibration‐induced disorders of the hand and arm, which are collectively referred to as “hand–arm vibration syndrome.'' The vibration direction has a great influence on the transmitted vibration. The present study focuses the effects of low‐frequency vertical vibration on hand to shoulder from handles of different size. The electrodynamic exciter is used for simulating vibration to a vertical handles of four different diameters. PULSE LabShop software is used for evaluating the magnitude of vibration in different frequency bands. The vibration characteristic data were acquired in the y_h axis at the wrist, elbow, and shoulder for bent arm and extended arm postures with vibration excitation of 4.5 m/s². Transmissibility characteristics are computed to determine the influence of handle diameter in y_h vibration transmitted to the hand–arm system. The magnitude of vibration transmitted within the hand, elbow, and shoulder was observed to be dependent on the handle size; larger handles cause higher vibration transmissibility. The results also show that the human hand–arm system in an extended arm posture amplifies the vibration transmitted than bent arm in a small difference. © 2011 Wiley Periodicals, Inc.     

Upper ocean response to Super Typhoon Tembin (2012) explored using multiplatform satellites and Argo float observations

Using multiplatform satellites and in situ Argo float observations, this study systematically examined the upper ocean response to Super Typhoon Tembin (2012) in the western north pacific, and the interaction between typhoon and a pre-existing cold core eddy (CCE) was particularly focused on. Significant sea surface temperature (SST) cooling and sea surface height anomaly (SSHA) decrease was detected along track after typhoon, with the maximum SST cooling and SSHA decrease reaching 4.0°C and 25 cm, respectively. The pre-existing CCE was located to the left of the typhoon track, resulting in an intriguing leftward bias of SST cooling. The maximum SST cooling appeared at about 25 km to the left of the typhoon track, with SST cooling to the left of the track 40–100% larger than that to the right. After typhoon, the CCE was expanded by 50% due to the typhoon’s cyclonic wind stress. The thermocline was uplifted by 15–25 m by the typhoon-induced upwelling. Typhoon-enhanced vertical mixing was inferred from high-resolution Argo float data based on the Gregg–Henyey–Polzin parameterization method. The diapycnal diffusivity reached 9 × 10^?4 m² s^?1 after typhoon, which was more than 10 times larger than that before typhoon.     

Frequency-dependence of discomfort caused by vibration and mechanical shocks

The frequency content of a mechanical shock is not confined to its fundamental frequency, so it was hypothesised that the frequency-dependence of discomfort caused by shocks with defined fundamental frequencies will differ from the frequency-dependence of sinusoidal vibration. Subjects experienced vertical vibration and vertical shocks with fundamental frequencies from 0.5 to 16 Hz and magnitudes from ±0.7 to ±9.5 ms^–2. The rate of growth of discomfort with increasing magnitude of motion decreased with increasing frequency of both motions, so the frequency-dependence of discomfort varied with the magnitudes of both motions and no single frequency weighting will be ideal for all magnitudes. At the frequencies of sinusoidal vibration producing greatest discomfort (4–16 Hz), shocks produced less discomfort than vibration with same peak acceleration or unweighted vibration dose value. Frequency-weighted vibration dose values provided the best predictions of the discomfort caused by different frequencies and magnitudes of vibration and shock.

Practitioner Summary: Human responses to vibration and shock vary according to the frequency content of the motion. The ideal frequency weighting depends on the magnitude of the motion. Standardised frequency-weighted vibration dose values estimate discomfort caused by vibration and shock but for motions containing very low frequencies the filtering is not optimum.     

Effects of whole-body vertical shock-type vibration on human ability for fine manual control

The effects of vertical (z-axis) whole-body shock-type vibration on the ability for fine manual control were examined. The amplitudes and frequency of the shocks was varied, but a constant frequency-weighted acceleration of 1·25 m/s² r. m. s. was maintained. The examination of the shock's effects was carried out using an experimental system that simulated the actual workplace of earth-moving machinery. Control was measured using a first-order pursuit tracking-test, in which a seated subject was asked to use both hands to direct a cursor on a monitor using a steering wheel. Although the magnitude of shocks (peak amplitude of 6-10 m/s²) and the number of shocks per unit time (shock cycle of 10-40 s) were varied, and two types of shock (symmetric and asymmetric) used, no shock effect could be found by calculating an integrated square of tracking error during the whole exposure time. The tracking error only increased significantly during the moments that the subjects were exposed to a symmetrically shaped shock that reached the highest peak value (for the experiment) of 10 m/s². The results suggested that shocks with peak amplitudes below defined value induce no evident effect on the steering of vehicles.     

Variations of surface boundary layer parameters associated with Cyclone Gonu over the Arabian Sea using QuikSCAT data

This study attempted to quantify the variations of the surface marine atmospheric boundary layer (MABL) parameters associated with the tropical Cyclone Gonu formed over the Arabian Sea during 30 May–7 June 2007 (just after the monsoon onset). These characteristics were evaluated in terms of surface wind, drag coefficient, wind stress, horizontal divergence, and frictional velocity using 0.5° × 0.5° resolution Quick Scatterometer (QuikSCAT) wind products. The variation of these different surface boundary layer parameters was studied for three defined cyclone life stages: prior to the formation, during, and after the cyclone passage. Drastic variations of the MABL parameters during the passage of the cyclone were observed. The wind strength increased from 12 to 22 m s^?1 in association with different stages of Gonu. Frictional velocity increased from a value of 0.1–0.6 m s^?1 during the formative stage of the system to a high value of 0.3–1.4 m s^?1 during the mature stage. Drag coefficient varied from 1.5 × 10^?3 to 2.5 × 10^?3 during the occurrence of Gonu. Wind stress values varied from 0.4 to 1.1 N m^?2. Wind stress curl values varied from 10 × 10^?7 to 45 × 10^?7 N m^?3. Generally, convergent winds prevailed with the numerical value of divergence varying from 0 to –4 × 10^?5 s^?1. Maximum variations of the wind parameters were found in the wall cloud region of the cyclone. The parameters returned to normally observed values in 1–3 days after the cyclone passage.     

All-terrain vehicle use in agriculture: Exposure to whole body vibration and mechanical shock

Whole body vibration (WBV) and mechanical shock were measured in 12 New Zealand farmers during their daily use of all-terrain vehicles (ATVs). As per the International Organization for Standardization (ISO) guidelines for WBV exposure, frequencies between 0 and 100 Hz were recorded via a seat-pad tri-axial accelerometer during 20 min of ATV use. The farmers were also surveyed to estimate seasonal variation in daily ATV usage as well as 7-day and 12-month prevalence of spinal pain. Frequency-weighted vibration exposure and total riding time were calculated to determine the daily vibration dose value (VDV). The daily VDV of 16.6 m/s^1.75 was in excess of the 9.1 m/s^1.75 action limit set by ISO guidelines suggesting an increased risk of low back injury from such exposure. However, the mean shock factor R, representing cumulative adverse health effects, was 0.31 indicating that these farmers were not exposed to excessive doses of mechanical shock. Extrapolation of daily VDV data to estimated seasonal variations of farmers in ATV riding time demonstrated that all participants would exceed the ISO recommended maximum permissible limits during the spring lambing season, as compared to lower exposures calculated for summer, autumn and winter. Low back pain was the most commonly reported complaint for both 7 day (50%) and 12 month prevalence (67%), followed by the neck (17% and 42%) and the upper back (17% and 25%) respectively. The results demonstrate high levels of vibration exposure within New Zealand farmers and practical recommendations are needed to reduce their exposure to WBV.     

An algorithm for the retrieval of sea surface wind fields using X-band TerraSAR-X data

TerraSAR-X (TS-X) is a new, fully polarized X-band synthetic aperture radar (SAR) satellite, which is a successor of the Spaceborne Imaging Radar X-band Synthetic Aperture Radar (SIR-X-SAR) and the SRTM. TS-X has provided high-quality image products over land and oceans for scientific and commercial users since its launch in June 2007. In this article, a new geophysical model function (GMF) is presented to retrieve sea surface wind speeds at a height of 10 m (U ₁₀) based on TS-X data obtained with VV polarization in the ScanSAR, StripMap and Spotlight modes. The X-band GMF was validated by comparing the retrieved wind speeds from the TS-X data with in situ observations, the high-resolution limited area model (HIRLAM) and QuikSCAT scatterometer measurements. The bias and root mean square (RMS) values were 0.03 and 2.33 m s^?1, respectively, when compared with the co-located wind measurements derived from QuikSCAT. To apply the newly developed GMF to the TS-X data obtained in HH polarization, we analysed the C-band SAR polarization models and extended them to the X-band SAR data. The sea surface wind speeds were retrieved using the X-band GMF from pairs of TS-X images obtained in dual-polarization mode (i.e. VV and HH). The retrieved results were also validated by comparing with QuikSCAT measurements and the results of the German Weather Service (DWD) atmospheric model. The obtained RMS was 2.50 m s^?1 when compared with the co-located wind measurements derived from the QuikSCAT, and the absolute error was 2.24 m s^?1 when compared with DWD results.