An unmanned aerial vehicle (UAV) aeromagnetic measurement system can precisely obtain large-scale data with high efficiency and low cost in regions with complex exploration conditions, which has aroused interest in the field of aerial survey. In this paper, based on the unmanned helicopter platform, an aeronautical magnetic field measurement system is integrated to complete the integration of a rotor UAV, magnetometers, and data recorders. Equipped with a three-axis fluxgate magnetometer for real-time flight compensation, the compensation deviation is ±0.052 nT, which meets the aeromagnetic survey specifications. The UAV can fly autonomously with a maximum load of 45 kg at a speed of 60 km/h for 2 h, and the wind resistance level is level 7. The system has completed a field test of 111.9 km in the Ma'anshan crisis mine region of China and collected 145,495 data points. Then, the adaptive down-sampling method is used to compress the data (to 1.7% of the original data), and it is applied to the three-dimensional magnetic inversion, which successfully obtains the spatial distribution characteristics of the underground orebody, improving the inversion efficiency while ensuring the target area resolution. Six favorable magnetite prospecting sites are delineated in the survey area through inversion results, which demonstrates the potential of the developed UAV aeromagnetic system in the exploration over the areas with complex terrain.
Hydrological model parameters are generally considered to be simplified representations that characterize hydrologic processes. Therefore, their influence on runoff simulations varies with climate and catchment conditions. To investigate the influence, a three-step framework is proposed, i.e., a Latin hypercube sampling (LHS-OAT) method multivariate regression model is used to conduct parametric sensitivity analysis; then, the multilevel-factorial-analysis method is used to quantitatively evaluate the individual and interactive effects of parameters on the hydrologic model output. Finally, analysis of the reasons for dynamic parameter changes is performed. Results suggest that the difference in parameter sensitivity for different periods is significant. The soil bulk density (SOL_BD) is significant at all times, and the parameter Soil Convention Service (SCS) runoff curve number (CN2) is the strongest during the flood period, and the other parameters are weaker in different periods. The interaction effects of CN2 and SOL_BD, as well as effective hydraulic channel conditions (CH_K2) and SOL_BD, are obvious, indicating that soil bulk density can impact the amount of loss generated by surface runoff and river recharge to groundwater. These findings help produce the best parameter inputs and improve the applicability of the model.
This letter studies distributed opportunistic channel access in a wireless network with decode-andforward relays. All the sources use channel contention to get transmission opportunity. If a source wins the contention, the channel state information in the first-hop channel (from the source to its relay) is estimated, and a decision is made for the winner source to either give up the transmission opportunity and let all sources start a new contention, or transmit to the relay. Once the relay gets the traffic, it may have a sequence of probings of the second-hop channel (from the relay to the destination). After each probing, if the second-hop channel is good enough, the relay transmits to the destination and completes the transmission process of the source; otherwise, the relay decides either to give up and let all sources start a new contention, or to continue to probe the second-hop channel. The optimal decision strategies for the two hops are derived in this letter. The first-hop strategy is a pure-threshold strategy, i.e., when the first-hop channel signal-to-noise ratio (SNR) is more than a threshold, the winner source should transmit to the relay, and subsequently the second-hop strategy should let the relay keep probing the second-hop channel until a good enough second-hop channel is observed. Simulation results show that our scheme is beneficial when the second-hop channels have larger average SNR. Index TermsDecode-and-forward relaying, opportunistic transmission, optimal stopping, throughput maximization.DF relaying network is considered in [6], in which each source-destination pair is aided by a DF relay. If a source has traffic to send, it sends a probing packet, and based on reception of the probing packet, the information of channel SNR in the first hop (from the source to its relay and to the destination) is obtained. Then the source decides to 1) give up, or 2) transmit with direct link, or 3) continue to probe the second hop (from the relay to the destination). If the source decides to probe the second hop, then the channel SNR of the second hop is estimated, and it is decided either to give up or to transmit (by using direct link or relay link, whichever March 19, 2018 DRAFT
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