Japanese Aerospace Exploration Agency Research Articles

Introduction to EarthCARE synthetic data using a global storm-resolving simulation

Abstract. Pre-launch simulated satellite data are useful to develop retrieval algorithms and to facilitate the rapid release of retrieval products after launch. Here we introduce the Japanese Aerospace Exploration Agency's (JAXA) EarthCARE synthetic data based on simulations using a 3.5 km horizontal-mesh global storm-resolving model. Global aerosol transport simulation results are added for aerosol retrieval developers. Synthetic data were produced corresponding to the four EarthCARE instrument sensors, namely a 94 GHz cloud-profiling radar (CPR), a 355 nm atmospheric lidar (ATLID), a seven-channel multispectral imager (MSI), and a broadband radiometer (BBR). JAXA EarthCARE synthetic data include a standard product with data for two orbits and a research product with shorter frames and more detailed instrument settings. In the research products, random errors in the CPR are considered based on the observation window, and noise in ATLID signals are added using a noise simulator. We consider the spectral misalignment effect of the visible and near-infrared MSI channels based on response functions depending on the angle from the nadir. We introduce plans for updating the JAXA EarthCARE synthetic data using large eddy simulation model data and the implementation of a three-dimensional radiation model. The JAXA EarthCARE synthetic data are available publicly.

Thermal expansion of oldhamite, CaS: Implication for the surface of Mercury

The temperature excursion variation of Mercury's surface may significantly change crystal structure of surface-comprising minerals. The thermal stability of oldhamite (CaS) was investigated to validate its presence on the Mercury's surface. In particular, X-Ray Powder Diffraction (XRPD) and Thermogravimetric Analyses (TGA) on synthetic powder calcium sulfide (Alfa Aesar) were performed with the aim of confirming its stability up to 723.15 K, the highest temperature that is recorded for the surface of Mercury.Our results by XRPD and TGA results confirmed that CaS phase is stable within the daily temperature excursion on Mercury surface. Thermal expansion analyses determined the thermal expansion volume coefficient of αV = 4.03 × 10−5 K−1. The results of this work support the presence of Ca-sulfide phases on Mercury's surface and provide valid tools for interpreting the data that will be collected by the BepiColombo space mission (European Space Agency and Japanese Aerospace Exploration Agency) to Mercury.

Processing reflectivity and Doppler velocity from EarthCARE's cloud-profiling radar: the C-FMR, C-CD and C-APC products

Abstract. The Earth Clouds, Aerosols and Radiation (EarthCARE) satellite mission is a joint effort by the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA). The EarthCARE mission features the first spaceborne 94 GHz cloud-profiling radar (CPR) with Doppler capability. The raw CPR observations and auxiliary information are used as input to three Level-2 (L2) algorithms: (1) C-APC: Antenna Pointing Characterization; (2) C-FMR: CPR feature mask and reflectivity; (3) C-CD: Corrected CPR Doppler Measurements. These algorithms apply quality control and corrections to the CPR primary measurements and derive important geophysical variables, such as hydrometeor locations, and best estimates of particle sedimentation fall velocities. The C-APC algorithm uses natural targets to introduce any corrections needed to the CPR raw Doppler velocities due to the CPR antenna pointing. The C-FMR product provides the feature mask based on only-reflectivity CPR measurements and quality-controlled radar-reflectivity profiles corrected for gaseous attenuation at 94 GHz. In addition, C-FMR provides best estimates of the path-integrated attenuation (PIA) and flags identifying the presence of multiple scattering in the CPR observations. Finally, the C-CD product provides the quality-controlled, bias-corrected mean Doppler velocity estimates (Doppler measurements corrected for antenna mispointing, non-uniform beam filling and velocity folding). In addition, the best estimate of the particle sedimentation velocity is estimated using a novel technique.

Distinguished aesthetics achievements and heritage in the space-age paintings inspired by space exploration

The purpose of this paper is to study the birth of space age and the distinguished achievements in the space-age painting aesthetics inspired by space exploration. It has been 66 years ever since the first successfully launch of the artificial satellite Sputnik 1 on October 4, 1957, generally recognized as the first year of space age. Exemplified by the best and most well-known “NASA Art Program”, many major space agencies have sponsored the art program. In Japan, the Japanese Aerospace Exploration Agency (JAXA) supports the art program through its Public Affairs Department. In the European Space Agency (ESA), one of its well-known residence artists is Aoife van Linden Tol. For 66 years of the space age, there are many outstanding painters with many distinguished achievements and heritage of aesthetic paintings created. In particular, Robert Rauschenberg's work “Buffalo II” painted in 1964 has become a classic masterpiece that realized the price of $ 88 million at Christie's auction in 2019.

Introduction to this special section: Planetary geophysics

While geophysical exploration of Earth is well established as a critical method for understanding planetary processes, many current and planned missions offer great opportunities for geophysicists to apply their skills and expertise to space exploration. Programs such as NASA's Artemis aiming to bring humans back to the moon and the James Webb Space Telescope for deep space imaging, the 10-year extension plan for the Chinese Lunar Exploration Program's Chang'e missions, the Japanese Aerospace Exploration Agency's Martian Moons eXploration program, and the European Space Agency's European Large Logistics Lander targeting the moon are just a few examples. NASA's Commercial Lunar Payload Services program proposes to send two commercial landers to the moon every year for the remainder of the decade. Several already-manifested payloads in the program involve geophysical instrumentation including heat flow probes, magnetotelluric sounding systems, and seismometers. Seismic data continue to arrive from NASA's InSight mission to Mars as the dusty solar panels still deliver a little energy, emphasizing that geophysics is and will remain an important tool for planetary exploration moving forward.

Calibration and performances of the MicrOmega instrument for the characterization of asteroid Ryugu returned samples

MicrOmega, a miniaturized near-infrared hyperspectral microscope, has been selected to characterize in the laboratory the samples returned from Ryugu by the Hayabusa2 mission. MicrOmega has been delivered to the Extraterrestrial Samples Curation Center of the Japanese Aerospace eXploration Agency at the Institute of Space and Astronautical Science in July 2020 and then mounted and calibrated to be ready for the analyses of the samples returned to Earth on December 6, 2020. MicrOmega was designed to analyze the returned samples within a field of view of 5 × 5mm2 and a spatial sampling of 22.5 µm. It acquires 3D near-infrared hyperspectral image-cubes by imaging the sample with monochromatic images sequentially covering the 0.99-3.65 µm spectral range, with a typical spectral sampling of 20cm-1. This paper reports the calibration processes performed to extract scientific data from these MicrOmega image-cubes. The determination of the instrumental response and the spectral calibration is detailed. We meet or exceed the goals of achieving an accuracy of ∼20% for the absolute reflectance level, 1% for the relative wavelength-to-wavelength reflectance, and <5nm for the peak position of the detected absorption features. For the nominal measurements of Ryugu samples with MicrOmega/Curation, the instrument performance also reaches a signal-to-noise ratio of >100 over the entire spectral range. By characterizing the entire collection of the returned samples at the microscopic scale, MicrOmega/Curation offers the potential to provide unprecedented insights into the composition and history of their asteroid parent body.

Large eddy simulation of aircraft at affordable cost: a milestone in computational fluid dynamics

Abstract While there have been numerous applications of large eddy simulations (LES) to complex flows, their application to practical engineering configurations, such as full aircraft models, have been limited to date. Recently, however, advances in rapid, high quality mesh generation, low-dissipation numerical schemes and physics-based subgrid-scale and wall models have led to, for the first time, accurate simulations of a realistic aircraft in landing configuration (the Japanese Aerospace Exploration Agency Standard Model) in less than a day of turnaround time with modest resource requirements. In this paper, a systematic study of the predictive capability of LES across a range of angles of attack (including maximum lift and post-stall regimes), the robustness of the predictions to grid resolution and the incorporation of wind tunnel effects is carried out. Integrated engineering quantities of interest, such as lift, drag and pitching moment will be compared with experimental data, while sectional pressure forces will be used to corroborate the accuracy of the integrated quantities. Good agreement with experimental $C_L$ data is obtained across the lift curve with the coefficient of lift at maximum lift, $C_{L,max}$ , consistently being predicted to within five lift counts of the experimental value. The grid point requirements to achieve this level of accuracy are reduced compared with recent estimates (even for wall modelled LES), with the solutions showing systematic improvement upon grid refinement, with the exception of the solution at the lowest angles of attack, which will be discussed later in the text. Simulations that include the wind tunnel walls and aircraft body mounting system are able to replicate important features of the flow field noted in the experiment that are absent from free air calculations of the same geometry, namely, the onset of inboard flow separation in the post-stall regime. Turnaround times of the order of a day are made possible in part by algorithmic advances made to leverage graphical processing units. The results presented herein suggest that this combined approach (meshing, numerical algorithms, modelling, efficient computer implementation) is on the threshold of readiness for industrial use in aeronautical design.

Spectral characterization of the craters of Ryugu as observed by the NIRS3 instrument on-board Hayabusa2

C-type rubble pile asteroid (162173) Ryugu was observed and characterized up close for a year and a half by the instruments on-board the Japanese Aerospace eXploration Agency (JAXA) Hayabusa2 spacecraft. The asteroid exhibits relatively homogeneous spectral characteristics at near-infrared wavelengths (~1.8–3.2 μm), including a very low reflectance factor, a slight positive (“red”) slope towards longer wavelengths, and a narrow absorption feature centered at 2.72 μm that is attributed to the presence of OH− in phyllosilicate minerals. Numerous craters have been identified at the surface that provide good candidates for identifying and studying younger and/or more recently exposed near-surface material to further assess potential spectral/compositional heterogeneities. We present here the results of a spectral survey of all previously identified and referenced craters (Hirata et al. 2020) based on reflectance data acquired by the NIRS3 spectrometer, with an emphasis on the spectral characteristics between different craters as well as with their surrounding terrain. At a global scale, the spectral properties inside and outside of craters are found to be very similar, indicating that subsurface material is either compositionally similar to material at the surface that has a longer exposure age or that material at Ryugu's optical surface is spectrally altered over relatively short timescales by external factors such as space weathering. Although, the imaging data from ONC camera suites show more morphological and color diversity in craters at a smaller scale than the resolution provided by the NIRS3 instrument, which could indicate a wider compositional diversity on Ryugu than that observed in the near-infrared and discussed in this paper. The 2.72 μm band depth exhibit a slight anti-correlation with the reflectance factor selected at 2 μm, which could indicate different surface properties (e.g., grain size and/or porosity) or different alteration processes (e.g., space weathering, shock metamorphism and/or solar heating). Four different spectral classes were identified based on their reflectance factor at 2 μm and 2.72 μm absorption strength. The most commonly spectral behavior associated with crater floors, is defined by a slightly lower reflectance at 2 μm and deeper band depth. These spectral characteristics are similar to those of subsurface material excavated by the Hayabusa2 small carry-on impactor (SCI) experiment, suggesting these spectral characteristics may represent materials with a younger surface exposure age. Alternatively, these materials may have experienced significant solar heating and desiccation to form finer grains that subsequently migrated towards and preferentially accumulated in areas of low geopotential, such as craters floors. It is believed that the Hayabusa2 mission successfully collected typical surface material as well as darker material excavated by the SCI experiment, and detailed analyses of those samples upon their return will allow for further testing of these formation and alteration hypotheses.

Research on innovative high performance and low-cost solid rocket fuel

The fuel for space access rockets represents a significant investment for space programmes as the energy required to propel the vehicles beyond our gravitational sphere is immense. Dr Yasuhiro Morita, from the Japanese Aerospace Exploration Agency (JAXA), and his team have been developing new, high performance, low-cost solid rocket fuels that could revolutionise the industry. Morita's ground-breaking solid fuel relies on the addition of a thermoplastic resin, and the process he has developed can be modified to allow more efficient manufacturing with smaller scale facilities.

Diamonds in the rubble

Two ancient asteroids with distinctive diamond-like shapes are revealing clues not only about their own formation, but that of the solar system as well. For the past three years, two spacecraft have been studying a pair of the most primitive solar system objects ever explored. The asteroids, Ryugu and Bennu, born of violent collisions in the asteroid belt, are some of the smallest objects ever visited by spacecraft. Ryugu is just over a kilometer across, and Bennu is about half as wide. The asteroid Bennu ejects particles from its surface in January 2019—a phenomenon captured in an image composed from multiple photos. Image credit: NASA/Goddard/University of Arizona/Lockheed Martin. But these small bodies are promising a huge bounty of data to astronomers over the next few years. Although the findings could revolutionize our understanding of the history, formation, and composition of asteroids, they may also tell us a little about the solar system during its infancy. That’s because these carbon-rich (1) asteroids, with their coal-dark surfaces, are also among the darkest bodies known in the solar system. Although that can make it difficult to observe them from Earth, studying them could tell us about the building blocks of life that such asteroids may have delivered to Earth early in the history of the solar system. Before researchers could hope to study these asteroids, they first had to reach them. This, by itself, was an enormous challenge. Only a handful of spacecraft have visited asteroids, and fewer still have managed to orbit one of these tiny, irregularly shaped objects. The Hayabusa spacecraft, launched by the Japanese Aerospace Exploration Agency (JAXA) in 2003, became the first to collect a sample of an asteroid. But the mission was beset by engine problems. Hayabusa’s prospects for returning with a sample remained uncertain for much of …

LiteBIRD Cryogenic Chain: 100 mK Cooling with Mechanical Coolers and ADRs

LiteBIRD is a JAXA-led L-Class mission aimed at the study of B-mode polarization of the cosmic microwave background. Measurements on 15 bandwidth from 34 to 448 GHz are made on two instruments, low-frequency telescope and medium- and high-frequency telescope. To reach the desired sensitivities, more than 4500 transition edge sensors detectors, used on both instruments, will be continuously cooled to 100 mK. The cryogenic design based on shield cooling and mechanical coolers is presented in this paper. Shield cooling will be done with passive cooling and 15 K pulse tube coolers. A single cryogenic chain will cool both instruments. A 4 K stage is cooled by a 4He Joule–Thomson cooler from Japanese Aerospace Exploration Agency, pre-cooled by Stirling coolers. Multistage adiabatic demagnetization refrigerator will be optimized to provide continuous cooling at 1.75 K, 300 mK and 100 mK with 2.2 µW of cooling power on the latter stage. Seven ADR stages provided by NASA (USA) and CEA (France) are required. Details on the thermal design, preliminary sizing and expected performance are presented.

Red-Edge Normalised Difference Vegetation Index (NDVI705) from Sentinel-2 imagery to assess post-fire regeneration

Obtaining post-fire information from a burnt region is of paramount importance in applications such as examining the disturbance of natural ecosystems and in providing crucial information to local authorities that have control on policymaking. This study uses freely available data from the European Space Agency's (ESA) Sentinel-2 satellite to create a Red-Edge Normalised Difference Vegetation Index (NDVI705) and combines the resulting layer with 30 m Digital Elevation Model (DEM) from the Japanese Aerospace Exploration Agency (JAXA) to assess topographical parameters (ie. slope steepness and aspect) which may have influenced the revegetation process. Additionally, weather data is combined with the aforementioned datasets to study the revegetation dynamics. A fire event which occurred in June 2016 in Evrychou, Cyprus, was chosen, as it was one of the largest fire events in the island and happened when the Sentinel-2 was already operational, hence a period of time spanning 14 months has been studied. The results have indicated an inconsistent NDVI705 change throughout the period. However, a significant improvement in NDVI705 values was observed in the months of spring 2017. The improvement in vegetation health was mostly observed on north-facing and less-steep slopes, something which corresponds with previous studies in northern-hemisphere Mediterranean climates. The results have also highlighted the ability to conduct a rapid and cost-effective post-fire assessment which can be scaled up or down depending on the fire size and which can be applied to any other environment where post-fire management is required.

Evaluation of open‐access global digital elevation models (AW3D30, SRTM, and ASTER) for flood modelling purposes

AbstractDigital elevation models (DEM) are fundamental for hydrologic and hydraulic modelling. Many practitioners rely on open‐access global data sets due to the cost and sparse coverage of sources of higher resolution. In 2016, the Japanese Aerospace Exploration Agency released the ALOS World 3D‐30m (AW3D30), an open‐access global elevation model at an horizontal resolution of 30 m. So far no published study has done an assessment of the flood modelling capabilities of this new product. The purpose of this investigation is to (a) assess the utility of the AW3D30 for flood modelling purposes and (b) compare its performance with regards to computed water levels and flood extent maps calculated using other freely available 30m DEM (e.g., SRTM and ASTER). For this comparison, the reference to reality is given by the maps computed using a light detection and ranging (LiDAR)‐based digital terrain model. This study is carried out in two catchments with contrasting topographic gradients. Results show that AW3D30 performs better than the SRTM. In mountainous regions, the results derived with the AW3D30 are comparable in skill to those obtained with a LiDAR‐derived digital surface model. This encouraging performance paves the way to more accurate modelling for both data‐scarce regions and global flood models.

Generation of Large-Scale Moderate-Resolution Forest Height Mosaic With Spaceborne Repeat-Pass SAR Interferometry and Lidar

This paper provides an overview of the scattering model, inversion approach, and validation of the application results for creating large-scale moderate-resolution (hectare-level) mosaics of forest height through using spaceborne repeat-pass SAR interferometry and lidar. By incorporating several improvements to the forest height inversion and mosaicking approach, the height estimation accuracy along with the robustness of this approach have been considerably enhanced from its originally reported accuracy of RMSE of 3–4 m at a 20-hectare aggregated pixel size to RMSE of 3–4 m on the order of 3–6 hectares. Furthermore, practical data processing schemes are provided in detail. Extensive validation results are demonstrated which include: 1) a forest height mosaic (total area of 11.6 million hectares) is generated for the U.S. states of Maine and New Hampshire using Japanese Aerospace Exploration Agency’s (JAXA) ALOS-1 InSAR correlation data and a small airborne lidar strip (44 000 hectares); 2) the mosaic height estimates are further compared with the available airborne lidar data and field measurements over both flat and mountainous areas; and 3) feasibility of using modern repeat-pass InSAR satellites with short repeat interval is also examined by using JAXA’s ALOS-2 data. This simple and efficient approach is a potential observational prototype with much smaller error budget for the future spaceborne repeat-pass L-band InSAR systems with small spatial baseline and moderate/large temporal baseline (such as NISAR) in combination with lidar (such as GEDI) on the application of large-scale forest height/biomass mapping. It also serves as a complementary tool to the spaceborne single-pass InSAR systems using InSAR/PolInSAR methods when full-pol data are not available and/or when the underlying topography slope causes problems for these approaches.

COMPARISON OF SUPERVISED CLASSIFICATION TECHNIQUES WITH ALOS PALSAR SENSOR FOR ROORKEE REGION OF UTTARAKHAND, INDIA

Abstract. The Advanced Land Observing Satellite (ALOS) is developed by the Japanese Aerospace Exploration Agency (JAXA) which was launched in the year 2006 for the Earth observation and exploration purpose. The ALOS was carrying PRISM, AVNIR-2 and PALSAR sensors for this purpose. PALSAR is L-Band synthetic aperture radar (SAR). The PALSAR sensor is designed in a way that it can work in all weather conditions with a resolution of 10 meters. In this research work we have made an investigation on the accuracy obtained from the various supervised classification techniques. We have compared the accuracy obtained by classifying the ALOS PALSAR data of the Roorkee region of Uttarakhand, India. The training ROI’S (Region of Interest) are created manually with the assistance of ArcGIS Earth and for the testing purpose, we have used the Global positioning system (GPS) coordinates of the region. Supervised classification techniques included in this comparison are Parallelepiped classification (PC), Minimum distance classification (MDC), Mahalanobis distance classification (MaDC), Maximum likelihood classification (MLC), Spectral angle mapper (SAM), Spectral information divergence (SID) and Support vector machine (SVM). Later, through the post classification confusion matrix accuracy assessment test is performed and the corresponding value of the kappa coefficient is obtained. In the result, we have concluded MDC as best in term of overall accuracy with 82.3634% and MLC with a kappa value of 0.7591. Finally, a peculiar relationship is developed in between classification accuracy and kappa coefficient.

The Global Precipitation Measurement (GPM) mission's scientific achievements and societal contributions: reviewing four years of advanced rain and snow observations.

Precipitation represents a life-critical energy and hydrologic exchange between the Earth's atmosphere and its surface. As such, knowledge of where, when, and how much rain and snow falls is essential for scientific research and societal applications. Building on the 17-year success of the Tropical Rainfall Measurement Mission (TRMM), the Global Precipitation Measurement (GPM) Core Observatory (GPM-CO) is the first U.S. National Aeronautical and Space Administration (NASA) satellite mission specifically designed with sensors to observe the structure and intensities of both rain and falling snow. The GPM-CO has proved to be a worthy successor to TRMM, extending and improving high-quality active and passive microwave observations across all times of day. The GPM-CO launched in early 2014, is a joint mission between NASA and the Japanese Aerospace Exploration Agency (JAXA), with sensors that include the NASA-provided GPM Microwave Imager and the JAXA-provided Dual-frequency Precipitation Radar. These sensors were devised with high accuracy standards enabling them to be used as a reference for inter-calibrating a constellation of partner satellite data. These intercalibrated partner satellite retrievals are used with infrared data to produce merged precipitation estimates at temporal scales of 30 minutes and spatial scales of 0.1° × 0.1°. Precipitation estimates from the GPM-CO and partner constellation satellites, provided in near real time and later reprocessed with all ancillary data, are an indispensable source of precipitation data for operational and scientific users. Advances have been made using GPM data, primarily in improving sensor calibration, retrieval algorithms, and ground validation measurements, and used to further our understanding of the characteristics of liquid and frozen precipitation and the science of water and hydrological cycles for climate/weather forecasting. These advances have extended to societal benefits related to water resources, operational numerical weather prediction, hurricane monitoring, prediction, and disaster response, extremes, and disease.

Detection of Forest Disturbance With Spaceborne Repeat-Pass SAR Interferometry

Focusing on open forests and woodlands within the Injune Landscape Collaborative Project research area in central southeast Queensland, Australia, and using dual-pol (HH and HV) ALOS PALSAR repeat-pass InSAR data (temporal baseline of 92 days), this paper explores the detection of forest disturbance from the spaceborne repeat-pass InSAR correlation magnitude by developing a simple and efficient forest disturbance detection approach. In particular, a generic physical InSAR scattering model is derived by accounting for the forest disturbance information as well as the normal temporal decorrelation effects that are later compensated for using the modified Random Volume over Ground model. Based on the generic model, a quantitative indicator of forest disturbance is retrieved, namely, disturbance index that varies from 0 (no disturbance) to 1 (complete deforestation). This index is compared with that identified using a time series of Landsat sensor data over a selective logging area and has a relative root mean square error of 13% at a spatial resolution of 0.8 ha. This paper highlights the use of the co-pol InSAR correlation magnitude for forest disturbance detection, which serves as a complimentary application to using the cross-pol counterpart for forest height inversion in a companion work. Given the global availability of this type of data (e.g., Japanese Aerospace Exploration Agency’s ALOS-1/2 and NASA-ISRO’s NISAR), the method is anticipated to contribute to the range of tools being developed for large-scale forest disturbance assessment and monitoring.

Evaluation of AMSR-E retrieval by detecting soil moisture decrease following massive dryland re-vegetation in the Loess Plateau, China

Knowledge of soil moisture, however varied in space and time, is critical for planning land use in water-limited drylands. Although satellite observations provide soil moisture instantaneously at large scale, few studies have addressed the application of satellite soil moisture retrieval in dryland areas with changing land use. In this study, we propose a method to evaluate the spatiotemporal variance of satellite retrieval based on the evaluation of soil moisture retrievals from the Advanced Microwave Scanning Radiometer on the Earth Observing System (AMSR-E). The operation period of this instrument (June 2002 to October 2011) covers the re-vegetation of the semi-arid Loess Plateau. Our study found that AMSR-E retrievals posted by the Japanese Aerospace Exploration Agency (JAXA) capture the spatiotemporal variance of soil moisture in the Loess Plateau, as well as the in-situ measured soil moisture decrease following the massive re-vegetation– despite it differing from the in-situ measurement in spatial scale. Soil moisture decrease in response to the massive re-vegetation occurred in a transition zone of grass-forest ecosystems with annual precipitation between 450 and 550mm. Our study suggests that current AMSR-E JAXA retrievals are an essential alternative to field measurement and model simulation, because they can identify the location and spatial extent of areas where soil moisture is sensitive to climate change and managed re-vegetation. To avoid the overconsumption of soil water and limited plant growth in transition zone, managers of dryland areas should pay special attention to species selection.

A comparison of SMOS and AMSR2 soil moisture using representative sites of the OzNet monitoring network

This paper evaluates the performance of different soil moisture products from AMSR2 and SMOS against the most representative stations within the Yanco study area in the Murrumbidgee catchment, in southeast Australia. AMSR2 Level 3 (L3) soil moisture products retrieved from two versions of brightness temperatures using the Japanese Aerospace eXploration Agency (JAXA) and the Land Parameter Retrieval Model (LPRM) algorithm were included. For the LPRM algorithm, two different parameterization methods were applied. Furthermore, two versions of SMOS L3 soil moisture product were assessed. The results are contrasted against the use of “random” stations. Accounting for all versions, frequencies and overpasses, the latest versions of the JAXA (JX2) and LPRM (LP3) products were found to surpass the earlier versions (JX1, LP1 and LP2). Soil moisture retrieval based on the latter version of brightness temperature and parameterization scheme improved when C-band observations were used but not X-band. However, X-band retrievals (r: 0.71, MAE: 0.07, RMSD: 0.08m3/m3) were found to perform better than C-band (r: 0.68–0.70, MAE: 0.07–0.09m3/m3, RMSD: 0.09–0.10m3/m3). Moreover, an intercomparison between different acquisition times (morning and evening) of AMSR2 X-band products found a better performance from evening overpasses (1:30pm; r: 0.69–0.77) as opposed to morning overpasses (1:30am; r: 0.47–0.66). In the case of SMOS, morning (6:00am; r: 0.77) retrievals were found to be superior over evening (6:00pm; r: 0.69) retrievals. Overall, both versions of JAXA products, the second and third versions of LPRM X-band products, and two versions of SMOS products were found to meet the mean average error (MAE) goal accuracy of the AMSR2 mission (MAE < 0.08 m3/m3) but none of the products achieved the SMOS goal of RMSD < 0.04 m3/m3. Furthermore, performance of the products differed depending on the statistic used to evaluate them. Consequently, considering the results in this study, JX2 products are recommended if both absolute and temporal accuracy of the soil moisture product is of importance, whereas LP3X products from evening observations and SMOS version 3.00 (SMOS2) products from morning overpasses are recommended if temporal accuracy is of greater importance.

Slip Model for the 25 November 2016 Mw 6.6 Aketao Earthquake, Western China, Revealed by Sentinel-1 and ALOS-2 Observations

On 25 November 2016 (UTC 14:24:30), an Mw 6.6 dextral strike-slip earthquake ruptured Aketao county in the northwestern portion of the Kongur Shan extensional system, western China. We extracted surface deformation maps and investigated the distribution of the coseismic slip of the 2016 Aketao earthquake by exploiting the Interferometric Synthetic Aperture Radar data imaged by the Sentinel-1 satellites of the European Space Agency and the ALOS-2 satellite of the Japanese Aerospace Exploration Agency. Assuming the crust of the earth is an elastic half-space homogeneous medium, the best fitting slip model suggests a dip angle of 78° for the seismogenic fault. The rupture of the 2016 Aketao earthquake may have consisted of two sub-events that occurred in rapid succession within a few seconds, resulting in two large discrete asperities with maximum slip of ~0.85 m, which were separated by a ~6 km-wide small slip gap. The maximum slip for the sub-event near the epicenter was mainly concentrated at a depth of ~10 km and that of the other at a depth of ~5 km. The estimated total seismic moment from the optimal slip model is 1.58 × 1019 N•m, corresponding to an event with a moment magnitude of 6.74. More than 65% of the aftershocks occurred in the areas of increased Coulomb failure stress, in which the stress was estimated to have been increased by at least 0.1 bar. Matching the potential barrier on the fault with the depth distribution of aftershocks implies that friction on the causative fault was heterogeneous, which may play a primary role in controlling the active behavior of the Muji fault.