Improved Hydrological Loading Models in South America: Analysis of GPS Displacements Using M-SSA

Environmental loading, in particular from continental water storage changes, induces geodetic station displacements up to several centimeters for the vertical components. We investigate surface deformation due to loading processes in South America using a set of 247 permanent GPS (Global Positioning System) stations for the 2003–2016 period and compare them to loading estimates from global circulation models. Unfortunately, some of the hydrological components, and in particular surface waters, may be missing in hydrological models. This is especially an issue in South America where almost half of the seasonal water storage variations are due to surface water changes, e.g., rivers and floodplains. We derive river storage variations by rerouting runoffs of global hydrology models, allowing a better agreement with the mass variations observed from GRACE (Gravity Recovery and Climate Experiment) mission. We extract coherent seasonal GPS displacements using Multichannel Singular Spectrum Analysis (M-SSA) and show that modeling the river storage induced loading effects significantly improve the agreement between observed vertical and horizontal displacements and loading models. Such an agreement has been markedly achieved in the Amazon basin. Whilst the initial models only explained half of the amplitude of GPS, the new ones compensate for these gaps and remain consistent with GRACE.

Using the photoload technique with double sampling to improve surface fuel loading estimates

Accurate surface fuel load estimates based on the planar intercept method require a considerable amount of time and cost. Recently the photoload method has been proposed as an alternative for sampling of fine woody surface fuels. To evaluate the use of photoload fuel sampling, six simulated fuel beds of 100 photoload visual estimates and destructively sampled fuel loads were generated at three levels of fuel loading (0.016, 0.060, and 0.120 kg m–2) and two levels of variability (coefficients of variation of ~42 and 85%). We assessed the accuracy and precision of simple random sampling with and without double sampling on surface fuel load estimation. Direct visual estimates often overestimated fuel loads where actual fuel loading was low and underestimated fuel loads where fuel loads were large. We found that double sampling with a classical regression estimation approach provided the most accurate and precise fuel load estimates, substantially improving the accuracy and precision achieved over standard photoload estimation when ń ≥ 20 and double sampling rate ≥20%. These results indicate that fine woody fuel loading estimation with the photoload technique can be improved by incorporating a double sampling approach.

Fine woody fuel particle diameters for improved planar intersect fuel loading estimates in Southern Rocky Mountain ponderosa pine forests

Fuel loading estimates from planar intersect sampling protocols for fine dead down woody surface fuels require an approximation of the mean squared diameter (d2) of 1-h (0–0.63 cm), 10-h (0.63–2.54 cm), and 100-h (2.54–7.62 cm) timelag size classes. The objective of this study is to determine d2 in ponderosa pine (Pinus ponderosa) forests of New Mexico and Colorado, USA in natural, partially harvested, and partially harvested and burned sites to improve fine woody fuel loading estimates. Resulting estimates were generally higher in the 1- and 10-h classes and lower in the 100-h classes when compared with previously published values from other regions. The partially harvested and burned values for 1- and 100-h classes were also significantly lower than in the other stand conditions. Using bootstrap analysis, it was determined that 35 samples would be sufficient to create an accurate estimate of d2 values.

The validity and reliability of a problem-based learning implementation questionnaire

Purpose: The aim of this paper is to provide evidence for the validity and reliability of a questionnaire for assessing the implementation of problem-based learning (PBL). This questionnaire was developed to assess the quality of PBL implementation from the perspective of medical school graduates. Methods: A confirmatory factor analysis was conducted to assess the validity of the questionnaire. The analysis was based on a survey of 225 graduates of a problem-based medical school in Indonesia. Results: The results showed that the confirmatory factor analysis model had a good fit to the data. Further, the values of the standardized loading estimates, the squared inter-construct correlations, the average variances extracted, and the composite reliabilities all provided evidence of construct validity. Conclusion: The PBL implementation questionnaire was found to be valid and reliable, making it suitable for evaluation purposes.

Analytical Model for Estimating Knee Loads During Ladder Climbing

We present a simple two-dimensional analytical model that estimates the knee joint loading during vertical ladder climbing. By developing a model with simplification assumptions, such as vertical ascent with no whole-body angular acceleration, we can grossly estimate knee loads under dynamic conditions using posture and whole-body acceleration. The model presented demonstrates that upward whole-body acceleration influences the knee load on the leading leg of the climber during ladder mounting and climbing. In an effort to define the preferential departure acceleration during ladder ascent for use with the model presented, we also present preliminary data of the initial step onto a fixed ladder. These data are combined with the model at the moment of initial stance foot departure to generate preliminary knee loading estimates. Where appropriate and possible, the authors have attempted to compare and validate the analytical model with published knee loading.

Volcanic ash infrared signature: realistic ash particle shapes compared to spherical ash particles

The reverse absorption technique is often used to detect volcanic clouds from thermal infrared satellite measurements. From these measurements particle size and mass loading may also be estimated using radiative transfer modelling. The radiative transfer modelling usually assumes that the ash particles are spherical. We calculate thermal infrared optical properties of highly irregular and porous ash particles and compare these with mass- and volume-equivalent spherical models. Furthermore, brightness temperatures pertinent to satellite observing geometry are calculated for the different ash particle shapes. Non-spherical shapes and volume-equivalent spheres are found to produce a detectable ash signal for larger particle sizes than mass-equivalent spheres. The assumption of mass-equivalent spheres for ash mass loading estimates will underestimate the mass loading by several tens of percent compared to morphologically complex inhomogeneous ash particles.