To parallelize data processing within BFT consensus protocols,Directed Acyclic Graph(DAG) structures have been integrated into consensus design, shaping the realm of DAG-based BFT protocols. Existing DAG-based protocols rely on theReliable Broadcast(RBC) protocol or its variants for block dissemination, which ensures consistency and totality properties of the data delivery. However, the inherent communication overhead ofO(n2) in RBC (wherenis the total replica count) results in an unwieldyO(n3) overhead in current DAG-based solutions, as each replica disseminates blocks through RBC in parallel. In response to this issue, we propose two new broadcast protocols:Provable Broadcast(PBC) andEnhanced ProvableBroadcast (EPBC). Both PBC and EPBC maintain the consistency property of data delivery, similar to RBC, while offering linear communication overhead without totality. Leveraging these broadcast protocols, we devise Wahoo, a novel DAG-based BFT protocol that significantly reduces communication overhead toO(n2). To address the absence of the totality property, we introduce a block retrieval mechanism to assist replicas in acquiring missing blocks. Additionally, under favorable conditions, Wahoo achieves a low latency of 4δ (where δ symbolizes the actual network delay), rivaling the best performance of existing DAG-based protocols. Various experiments showcase Wahoo’s high performance, owing to its substantially reduced communication overhead.

To enable parallel processing, the Directed Acyclic Graph (DAG) structure is introduced to the design of asyn-chronous Byzantine Fault Tolerant (BFT) consensus protocols, known as DAG-based BFT. Existing DAG-based BFT protocols operate in successive waves, with each wave containing three or four Reliable Broadcast (RBC) rounds to broadcast data, resulting in high latency due to the three communication steps required in each RBC. For instance, Tusk, a state-of-the-art DAG-based BFT protocol, has a good-case latency of 7 communication steps and an expected worst latency of 21 communication steps. To reduce latency, we propose GradedDAG, a new DAG-based BFT consensus protocol based on our adapted RBC called Graded RBC (GRBC) and the Consistent Broadcast (CBC), with each wave consisting of only one GRBC round and one CBC round. Through GRBC, a replica can deliver data with a grade of 1 or 2, and a non-faulty replica delivering the data with grade 2 can ensure that more than 2/3 of replicas have delivered the same data. Meanwhile, through CBC, data delivered by different non-faulty replicas must be identical. In each wave, a block in the GRBC round will be elected as the leader. If a leader block has been delivered with grade 2, it and all its ancestor blocks can be committed. GradedDAG offers a good-case latency of 4 communication steps and an expected worst latency of 7.5 communication steps, significantly lower than the state-of-the-art. Experimental results demonstrate GradedDAG's feasibility and efficiency.

The popularity of blockchain technology has revived interest in Byzantine Fault Tolerance (BFT) consensus protocols. However, existing protocols suffer from high latency, especially when the system is deployed in a worldwide manner. Taking Practical Byzantine Fault Tolerance (PBFT), the best-known and de-facto standard of BFT consensus protocol, as an example, it requires at least three phases to commit a request. Although some works attempt to shorten the number of phases by proposing a fast-path commitment rule, they either sacrifice resilience or subvert security.

The Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) is an airborne total-power radiometer that, after the recent modification, measures radiation at the nine frequencies of 50.3, 52.8, 89 (dual-polarized), 165 (dual-polarized), 183.3 ± 1, 183.3 ± 3, and 183.3 ± 7 GHz. During the Mid-latitude Continental Convective Clouds Experiment of April 22-June 1, 2011, it is programmed to acquire radiometric measurements in both conical and cross-track scans nearly simultaneously. Its new capability of measuring scattering signatures from storm-associated hydrometeors in dual polarization at both 89 and 165 GHz is illustrated and reported in this paper. We find that, from all seven flights over stratiform rain and convective storms, the polarization index (PI), is small but definitively positive at both frequencies, and generally (89 GHz) ≤PI(165 GHz). When brightness temperaturesTbps are ≥ 240 K, there is a significant correlation betweenPIand the brightness difference between the two frequencies (dTbp=Tbp(89) -Tbp(165) , wherepis either vertical V or horizontal H polarization); linear regression between these two parameters gives positive slopes for all seven events, with 165-GHz slopes generally larger the 89-GHz ones. Observations from five special sensor microwave imager/sounder passes in near concurrence with the CoSMIR measurements are examined for the relation betweenPI(91.665 GHz) anddTbh(91.665 GHz-150 GHz). The regression slopes are again found to be positive, and their magnitudes show some correspondence to those of CoSMIR. The significance of these findings to improvement in the parameter retrievals of hydrometeors is briefly discussed.

In this paper, recently developed dual polarization 643 GHz and single polarization 874 GHz receivers for airborne CoSSIR, Compact Scanning Sub-millimeter wave Imaging Radiometer were utilized for ice cloud measurements. The results show that the brightness temperature map clearly demonstrates the recent advance in sub-millimeter wave radiometry for ice cloud sensing. The 874 GHz radiometer greatly improves the CoSSIR sensitivity to small ice particles. This implies that CoSSIR is able to pick up the measurements of ice clouds where the visible and inferred approaches left behind, i.e. saturated. The polarization measurement capability at 643 GHz can provide information on particle shapes, as well as improve the accuracy of the ice cloud parameters retrievals, e.g., ice water path and particle size.

Previous water vapor profiling by millimeterwave radiometry using the 183-GHz absorption line is generally limited to an altitude range of 0-11 km. The additional measurements at the frequencies of 380.2 0.8, 380.2 1.8, 380.2 3.3, and 380.2 6.2 GHz by the new airborne compact scanning submillimeterwave imaging radiometer (CoSSIR) reported in this paper can extend this profiling capability up to an altitude of about 15 km. This is demonstrated by recent CoSSIR measurements onboard the NASA WB-57 aircraft in a flight from Texas to Costa Rica on January 14, 2006. Retrievals of water vapor mixing ratio were performed at eight altitudes of 1, 3, 5, 7, 9, 11, 13, and 15 km from the CoSSIR data set acquired at observational angles of 0 and 53.4. The results were compared with other available measurements from near-concurrent satellites. A very good agreement was found between the collocated values of total precipitable water (TPW) derived from the CoSSIR-retrieved water vapor profiles and those estimated from Tropical Rainfall Measuring Mission Microwave Imager; the average TPW differences range between 0.30 and 0.64 cm, depending on CoSSIR's observational angles. The accuracy of the retrievals was inferred from an analysis of inflight CoSSIR radiometric signal fluctuations.

The X-Band Lightweight Rainfall Radiometer using synthetic thinned aperture radiometer technology (LRR-X STAR) is an aircraft microwave sensor that is jointly under development by the NASA Goddard Space Flight Center and the University of Michigan. It operates at 10.7 GHz with 86+ simultaneous 2.1/spl deg/ HPBW antenna beams distributed over a /spl plusmn/ 45/spl deg/ cross track field of view to permit pushboom imaging. It is intended to address several pressing issues related to the Global Precipitation Measurement (GPM) Mission, for which it is a science and technology testbed instrument. In terms of technology readiness, LRR-STAR will evaluate and validate the design approaches being taken by each of its critical subsystems. At the system level, it will validate the calibration methodology used to produce Level 1 brightness temperature imagery. All electrical, mechanical and thermal subsystems of the LRR-STAR are currently in development and several key subsystems have had successful prototype fabrication and laboratory testing. An overview of the instrument design is presented, together with a status report on the hardware development.