Land surface temperature (LST) is an important physical quantity at the land-atmosphere interface. Since 2016 the Collection 6 (C6) MODIS LST product is publicly available, which includes three ...refinements over bare soil surfaces compared to the Collection 5 (C5) MODIS LST product. To encourage the use of the C6 MODIS LST product in a wide range of applications, it is necessary to evaluate the accuracy of the C6 MODIS LST product. In this study, we validated the C6 MODIS LST product using temperature-based method over various land cover types, including grasslands, croplands, cropland/natural vegetation mosaic, open shrublands, woody savannas, and barren/sparsely vegetated. In situ measurements were collected from various sites under different atmospheric and surface conditions, including seven SURFRAD sites (BND, TBL, DRA, FPK, GCM, PSU, and SXF) in the United States, three KIT sites (EVO, KAL, and GBB) in Portugal and Namibia, and three HiWATER sites (GBZ, HZZ, and HMZ) in China. The spatial representativeness of the in situ measurements at each site was separately evaluated during daytime and nighttime using all available clear-sky ASTER LST products at 90 m spatial resolution. Only six sites during daytime are selected as sufficiently homogeneous sites despite the usually high spatial thermal heterogeneity, whereas during nighttime most sites can be considered to be thermally homogeneous and have similar LST and air temperature. The C6 MODIS LST product was validated using in situ measurements from the selected homogeneous sites during daytime and nighttime: except for the GBB site, large RMSE values (>2 K) were obtained during daytime. However, if only satellite LST with a high spatial thermal homogeneity on the MODIS pixel scale are used for LST validation, the best daytime accuracy (RMSE <1.3 K) for the C6 MODIS LST product is achieved over the BND and DRA sites. Except for the DRA site, the RMSE values during nighttime are <2 K at the selected homogeneous sites. Furthermore, the accuracy of the C6 MODIS LST product was compared with that of the C5 MODIS LST product during nighttime at the selected homogeneous sites. Except for the GBB site, there are only small differences (<0.4 K) between the RMSE values for the C5 and C6 MODIS LST products.
•C6 MODIS LST product was validated using the temperature-based method.•We compared with C5 and C6 MODIS LST products over various land cover types.•Except for bare soil sites, the RMSE difference between C5 and C6 is <0.4 K.•The existing issues of C6 MODIS LST product were analyzed and discussed.
Soil moisture is widely recognized as a key parameter in the mass and energy balance between the land surface and the atmosphere and, hence, the potential societal benefits of an accurate estimation ...of soil moisture are immense. Recently, scientific community is making great effort for addressing the estimation of soil moisture over large areas through in situ sensors, remote sensing and modelling approaches. The different techniques used for addressing the monitoring of soil moisture for hydrological applications are briefly reviewed here. Moreover, some examples in which in situ and satellite soil moisture data are successfully employed for improving hydrological monitoring and predictions (e.g., floods, landslides, precipitation and irrigation) are presented. Finally, the emerging applications, the open issues and the future opportunities given by the increased availability of soil moisture measurements are outlined.
The spatial scale mismatch between satellite and in-situ -based measurements can be reduced by deploying multiple in-situ sites within the coarse pixel. However, upscaling in-situ measurements from ...the ground-support scale to the coarse pixel scale is still necessary due to their "point" measurement characteristics. The previous upscaling methods were generally developed merely for the in-situ measurements. Nevertheless, the uncertainty of in-situ measurements such as measurement errors and spatial representativeness errors was not dealt with. Consequently, the upscaling results inevitably suffer from errors, which will finally propagate into the pixel scale ground "truth". For the first time, this study presents an improved upscaling method with the consideration of the uncertainty of in-situ measurements based on the error theory and measurement adjustment theory. The effectiveness of the corrected upscaling coefficients was evaluated by comparing the accuracy of the corrected upscaling results with those based on the upscaling coefficients without considering the uncertainty of in-situ measurements. The results indicate that the accuracy of the upscaling results can be enhanced by 11.06% in the condition in which in-situ measurements suffer from large uncertainty. However, if the uncertainty of in-situ measurements is negligible, the corrected upscaling model is not necessary because it does not bring many benefits. Although the effectiveness of this method was only tested on a limited study area, it makes an important first step toward a higher precision pixel-scale ground "truth", especially when the uncertainty of in-situ measurements is non-negligible.
Long‐term stability of catalysts is an important factor in the chemical industry. This factor is often underestimated in academic testing methods, which may lead to a time gap in the field of ...catalytic research. The deactivation behavior of an industrially relevant Cu/ZnO/Al2O3 catalyst for the synthesis of methanol is reported over a period of 148 days time‐on‐stream (TOS). The process was investigated by a combination of quasi in situ and ex situ analysis techniques. The results show that ZnO is the most dynamic species in the catalyst, whereas only slight changes can be observed in the Cu nanoparticles. Thus, the deactivation of this catalyst is driven by the changes in the ZnO moieties. Our findings indicate that methanol synthesis is an interfacially mediated process between Cu and ZnO.
ZnO is the key for stability: Long‐term stability tests of catalysts are often underestimated in academia, despite industrial requirements. The deactivation of an industrially relevant Cu/ZnO/Al2O3 catalyst for the synthesis of methanol was investigated over a period of 148 days time‐on‐stream, with a combination of quasi in situ and ex situ analysis techniques. The findings indicate that controlling the polymorphism of ZnO is the key to the stability of the investigated catalytic system.
Additive manufacturing (AM) of superalloys has been attracting increasing interest. While most studies focus on the processability and mechanical properties of the finished product, it is also ...necessary to understand the phase transformations during the consecutive melting processes. Herein, the precipitation and dissolution of the γ′ phase in the Ni‐base superalloy CMSX‐4 in a selective laser melting process is reported. These phase transformations are studied in situ by small‐angle X‐ray scattering (SAXS) during AM. Concurrent wide‐angle X‐ray scattering (WAXS) provides information on the evolution of lattice parameters and temperature during the process. Additional thermal and thermodynamic simulations are carried out to support the experiments. The investigations are focused on the influence of different beam scanning strategies as well as the effect of laser power and scanning speed on the phase transformation dynamics. Due to the high cooling and heating rates inherent to AM, phase transformations occur far off equilibrium. Both precipitation and dissolution of γ′ phase are observed. The scan strategies are shown to have a considerable effect on the phase transformation dynamics, which exceed the impact of the beam parameters. The capability of combined SAXS and WAXS for the in situ study of phase transformations in AM processes is demonstrated.
Phase transformations during additive manufacturing of the nickel‐base superalloys CMSX‐4 are measured in situ using small‐angle and wide‐angle X‐ray scattering. Supported by thermal simulations, it is shown that the phase transformations occur highly off‐equilibrium. X‐ray scattering allows the qualitative observation of formation and dissolution of the γ′ phase within the solidified material during the deposition of successive layers.
Our knowledge of the properties of coronal mass ejections (CMEs) in the inner heliosphere is constrained by the relative lack of plasma observations between the Sun and 1 AU. In this work, we present ...a comprehensive catalog of 47 CMEs measured in situ measurements by two or more radially aligned spacecraft (MESSENGER, Venus Express, STEREO, Wind/ACE). We estimate the CME impact speeds at Mercury and Venus using a drag‐based model and present an average propagation profile of CMEs (speed and deceleration/acceleration) in the inner heliosphere. We find that CME deceleration continues past Mercury's orbit but most of the deceleration occurs between the Sun and Mercury. We examine the exponential decrease of the maximum magnetic field strength in the CME with heliocentric distance using two approaches: a modified statistical method and analysis from individual conjunction events. Findings from both the approaches are on average consistent with previous studies but show significant event‐to‐event variability. We also find the expansion of the CME sheath to be well fit by a linear function. However, we observe the average sheath duration and its increase to be fairly independent of the initial CME speed, contradicting commonly held knowledge that slower CMEs drive larger sheaths. We also present an analysis of the 3 November 2011 CME observed in longitudinal conjunction between MESSENGER, Venus Express, and STEREO‐B focusing on the expansion of the CME and its correlation with the exponential falloff of the maximum magnetic field strength in the ejecta.
Key Points
A comprehensive catalog of 47 CMEs observed in conjunction between radially aligned spacecraft in the inner heliosphere
Conjunction events reveal that the sheath duration expands nearly linearly but independently of the initial CME speed
The average decrease of the CME maximum magnetic field strength agrees with past results but individual events show significant deviations
We performed TRIUMF in situ measurements of the levels and kinetics of radiation-induced attenuation (RIA) caused by protons in different bulk optical glasses. Two SCHOTT radiation-hardened glasses ...(doped with Cerium) and six standard optical glasses (without Cerium) have been characterized. We compared the proton RIA kinetics with those resulting from in situ X-ray irradiations performed at dose and dose rate equivalent to the proton testing ones. The RIA spectra and kinetics are quite comparable in both cases, showing that X-rays can efficiently be used to estimate the RIA caused by protons. To better discuss the differences, we performed Monte Carlo calculations with GEANT4 of the energy deposition coefficient for each glass, according to its composition, and for the different beams. We complete our experimental characterization by comparing our data with those measured by the European Space Agency on the same glasses after <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-irradiation. Protons, X-rays and <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-rays cause RIA with very close spectral dependences, producing the same defects at similar concentration levels. We also demonstrated that the optimized setup for the in situ RIA characterization of bulk materials is very suitable for measurements under collimated particles beam.
Predicting algal blooms has become a priority for scientists, municipalities, businesses, and citizens. Remote sensing offers solutions to the spatial and temporal challenges facing existing lake ...research and monitoring programs that rely primarily on high-investment, in situ measurements. Techniques to remotely measure chlorophyll a (chl a) as a proxy for algal biomass have been limited to specific large water bodies in particular seasons and narrow chl a ranges. Thus, a first step toward prediction of algal blooms is generating regionally robust algorithms using in situ and remote sensing data. This study explores the relationship between in-lake measured chl a data from Maine and New Hampshire, USA lakes and remotely sensed chl a retrieval algorithm outputs. Landsat 8 images were obtained and then processed after required atmospheric and radiometric corrections. Six previously developed algorithms were tested on a regional scale on 11 scenes from 2013 to 2015 covering 192 lakes. The best performing algorithm across data from both states had a 0.16 correlation coefficient (R²) and P ≤ 0.05 when Landsat 8 images within 5 d, and improved to R² of 0.25 when data from Maine only were used. The strength of the correlation varied with the specificity of the time window in relation to the in-situ sampling date, explaining up to 27% of the variation in the data across several scenes. Two previously published algorithms using Landsat 8’s Bands 1–4 were best correlated with chl a, and for particular late-summer scenes, they accounted for up to 69% of the variation in in-situ measurements. A sensitivity analysis revealed that a longer time difference between in situ measurements and the satellite image increased uncertainty in the models, and an effect of the time of year on several indices was demonstrated. A regional model based on the best performing remote sensing algorithm was developed and was validated using independent in situ measurements and satellite images. These results suggest that, despite challenges including seasonal effects and low chl a thresholds, remote sensing could be an effective and accessible regional-scale tool for chl a monitoring programs in lakes.
The seeder–feeder mechanism has been observed to enhance orographic precipitation in previous studies. However, the microphysical processes active in the seeder and feeder region are still being ...understood. In this paper, we investigate the seeder and feeder region of a mixed-phase cloud passing over the Swiss Alps, focusing on (1) fallstreaks of enhanced radar reflectivity originating from cloud top generating cells (seeder region) and (2) a persistent low-level feeder cloud produced by the boundary layer circulation (feeder region). Observations were obtained from a multi-dimensional set of instruments including ground-based remote sensing instrumentation (Ka-band polarimetric cloud radar, microwave radiometer, wind profiler), in situ instrumentation on a tethered balloon system, and ground-based aerosol and precipitation measurements. The cloud radar observations suggest that ice formation and growth were enhanced within cloud top generating cells, which is consistent with previous observational studies. However, uncertainties exist regarding the dominant ice formation mechanism within these cells. Here we propose different mechanisms that potentially enhance ice nucleation and growth in cloud top generating cells (convective overshooting, radiative cooling, droplet shattering) and attempt to estimate their potential contribution from an ice nucleating particle perspective. Once ice formation and growth within the seeder region exceeded a threshold value, the mixed-phase cloud became fully glaciated. Local flow effects on the lee side of the mountain barrier induced the formation of a persistent low-level feeder cloud over a small-scale topographic feature in the inner-Alpine valley. In situ measurements within the low-level feeder cloud observed the production of secondary ice particles likely due to the Hallett–Mossop process and ice particle fragmentation upon ice–ice collisions. Therefore, secondary ice production may have been partly responsible for the elevated ice crystal number concentrations that have been previously observed in feeder clouds at mountaintop observatories. Secondary ice production in feeder clouds can potentially enhance orographic precipitation.
Bifunctional nanocrystals with integrated plasmonic and catalytic activities hold great promise for analyzing chemical reactions by in situ surface‐enhanced Raman spectroscopy. This Minireview gives ...a brief introduction to the general strategies for designing such nanocrystals, followed by four typical examples, including their fabrication, characterization, and potential limitation. We then use the reduction of 4‐nitrothiophenol and oxidation of 4‐aminothiophenol as two model systems to demonstrate the capabilities of these bifunctional nanocrystals to monitor chemical reactions for the elucidation of reaction mechanisms and measurement of kinetics. We conclude with perspectives on further development of these bifunctional nanocrystals into a viable platform for investigating other types of catalytic reactions.
SERS them right: Bifunctional nanocrystals with integrated plasmonic and catalytic activities hold great promise for analyzing chemical reactions by in situ surface‐enhanced Raman spectroscopy (SERS). This Minireview gives a brief introduction to the general strategies for designing such nanocrystals and their use in the elucidation of reaction mechanisms and measurement of kinetics.
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