A variety of industrial applications are deployed in underground environments, such as soil condition assessment and pipeline monitoring (PM). Wireless underground sensor networks (WUSNs) are capable of continuously monitoring pipelines and promptly alerting any anomaly of entities. However, underground soils significantly influence the traditional WUSNs connectivity success. Long Range (LoRa), being a leading low-power wide-area networks (LPWANs) technology, provides a new solution for underground industrial monitoring with its advantages in long-range capability and ultra-low power consumption. Nevertheless, the LoRa-based link quality characteristics have not yet been quantitatively evaluated for WUSNs. In this paper, the channel models of both the underground-to-aboveground (UG2AG) and aboveground-to-underground (AG2UG) communications are investigated. We experimentally analyze the impact of the propagation direction, burial depth and LoRa physical layer parameters on the in-situ LoRa propagation performance. Received Signal Strength Indictor (RSSI), Signal to Noise Ratio (SNR), Packet Deliver Ratio (PDR) are characterized for both communication channels in LoRa-based WUSNs. The semi-empirical path loss models are successfully verified by our field results, and we demonstrate that the communication range can be greater than 50 m at the burial depth of 0.4 m by adjusting the LoRa transmission/receiving settings. The combination of RSSI and SNR can be a better indicator of PDR than relying on either of them alone. Finally, Frame Error Rate (FER) is calculated to estimate the link performance with EM interferences. These results successfully demonstrate the advantages of LoRa for PM applications, which serve the first step towards the efficient protocol development of LoRa-based WUSNs.

We present a design of a low-frequency perfect acoustic absorption metaporous composite with frequency tunability and the insensitivity to the incident angle based on a critical coupling mechanism. The metaporous composite is constructed by embedding an Archimedean spiral structure in traditional porous materials. We verified the tunable balance of the dissipation and leakage of the metaporous composite by adjusting the slit orientation of the embedded spiral and the width and depth of the porous materials. Our simulations show that the composite's thickness is 1/20th of the corresponding wavelength at the perfect absorption (PA). Experiment and complex frequency plane analysis confirm the perfect acoustic absorption. The simulations show that the acoustic absorption of the system is highly efficient (0.95), up to a large oblique incidence, e.g., $60°$ . We also achieve the dual-band PA by embedding two spirals or using the higher order mode of a single spiral. The proposed composite absorber provides promising potential for low-frequency noise reduction applications.

We present the results of an assessment of ice surface elevation measurements from NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) along the CHINARE (CHINese Antarctic Research Expedition) route near the Amery Ice Shelf in East Antarctica. The validation campaign was designed and implemented in cooperation with the 36th CHINARE Antarctic expedition from December 2019 to February 2020. The assessment of the ICESat-2 geolocated photon product (ATL03) and land ice elevation product (ATL06) was performed based on coordinated multi-sensor observations using two roof-mounted kinematic global navigation satellite system (GNSS) receivers, two line arrays of corner cube retroreflectors (CCRs), two sets of retroreflective target sheets (RTSs), and two unmanned aerial vehicles (UAVs) with cameras. This systematic validation of the ICESat-2 data covered a variety of Antarctic ice surface conditions along the 520 km traverse from the coastal Zhongshan Station to the inland Taishan Station. This comprehensive investigation is complementary to the 750 km traverse validation of flat inland Antarctica containing a 300 km latitude traverse of 88^∘ S by the mission team (Brunt et al., 2021). Overall, the validation results show that the elevation of the ATL06 ice surface points is accurate to 1.5 cm with a precision of 9.1 cm along the 520 km CHINARE route. The elevation of the ATL03 photons has an offset of 2.1 cm from a GNSS-surveyed CCR and is accurate to 2.5 cm with a precision of 2.7 cm as estimated by using RTSs. The validation results demonstrate that the estimated ICESat-2 elevations are accurate to 1.5–2.5 cm in this East Antarctic region, which shows the potential of the data products for eliminating mission biases by overcoming the uncertainties in the estimation of mass balance in East Antarctica. It should be emphasized that the results based on the CCR and RTS techniques can be improved by further aggregation of observation opportunities for a more robust assessment. The developed validation methodology and sensor system can be applied for continuous assessment of ICESat-2 data, especially for calibration against potential degradation of the elevation measurements during the later operation period.

Permafrost is extremely sensitive to variance in external hydrothermal conditions. InSAR has advantages in monitoring surface deformation with decent temporal and spatial resolution as well as millimeter precision. In particular, the StaMPS-InSAR method can remove the disturbances of inaccurate digital elevation model (DEM), atmospheric delays and spatiotemporal decorrelation for an accurate estimation of temporal surface deformation. In this paper, a set of ascending and descending Sentinel-1 imageries spanning from March 2017 to June 2018 were acquired and processed by StaMPS-InSAR in order to investigate dynamic changes of permafrost in Wudaoliang Basin, Qinghai-Tibet Plateau (QTP). The results revealed that significant seasonal changes of permafrost, namely subsidence (thawing) in summer and uplift (freezing) in winter, can be observed throughout the Wudaoliang region. This study shows the StaMPS-InSAR analysis on Sentinel-1 datasets has great potential in regional permafrost investigation.