Comparisons of passive microwave remote sensing sea ice concentrations with ship-based visual observations during the CHINARE Arctic summer cruises of 2010–2018

In order to apply satellite data to guiding navigation in the Arctic more effectively,the sea ice concentrations(SIC)derived from passive microwave(PM)products were compared with ship-based visual observations(OBS)collected during the Chinese National Arctic Research Expeditions(CHINARE).A total of 3667 observations were collected in the Arctic summers of 2010,2012,2014,2016,and 2018.PM SIC were derived from the NASA-Team(NT),Bootstrap(BT)and Climate Data Record(CDR)algorithms based on the SSMIS sensor,as well as the BT,enhanced NASA-Team(NT2)and ARTIST Sea Ice(ASI)algorithms based on AMSR-E/AMSR-2 sensors.The daily arithmetic average of PM SIC values and the daily weighted average of OBS SIC values were used for the comparisons.The correlation coefficients(CC),biases and root mean square deviations(RMSD)between PM SIC and OBS SIC were compared in terms of the overall trend,and under mild/normal/severe ice conditions.Using the OBS data,the influences of floe size and ice thickness on the SIC retrieval of different PM products were evaluated by calculating the daily weighted average of floe size code and ice thickness.Our results show that CC values range from 0.89(AMSR-E/AMSR-2 NT2)to 0.95(SSMIS NT),biases range from−3.96%(SSMIS NT)to 12.05%(AMSR-E/AMSR-2 NT2),and RMSD values range from 10.81%(SSMIS NT)to 20.15%(AMSR-E/AMSR-2 NT2).Floe size has a significant influence on the SIC retrievals of the PM products,and most of the PM products tend to underestimate SIC under smaller floe size conditions and overestimate SIC under larger floe size conditions.Ice thickness thicker than 30 cm does not have a significant influence on the SIC retrieval of PM products.Overall,the best(worst)agreement occurs between OBS SIC and SSMIS NT(AMSR-E/AMSR-2 NT2)SIC in the Arctic summer.

Physical and optical characteristics of sea ice in the Pacific Arctic Sector during the summer of 2018

The reduction in Arctic sea ice in summer has been reported to have a significant impact on the global climate.In this study,Arctic sea ice/snow at the end of the melting season in 2018 was investigated during CHINARE-2018,in terms of its temperature,salinity,density and textural structure,the snow density,water content and albedo,as well as morphology and albedo of the refreezing melt pond.The interior melting of sea ice caused a strong stratification of temperature,salinity and density.The temperature of sea ice ranged from–0.8℃ to 0℃,and exhibited linear cooling with depth.The average salinity and density of sea ice were approximately 1.3 psu and 825 kg/m3,respectively,and increased slightly with depth.The first-year sea ice was dominated by columnar grained ice.Snow cover over all the investigated floes was in the melt phase,and the average water content and density were 0.74%and 241 kg/m3,respectively.The thickness of the thin ice lid ranged from 2.2 cm to 7.0 cm,and the depth of the pond ranged from 1.8 cm to 26.8 cm.The integrated albedo of the refreezing melt pond was in the range of 0.28–0.57.Because of the thin ice lid,the albedo of the melt pond improved to twice as high as that of the mature melt pond.These results provide a reference for the current state of Arctic sea ice and the mechanism of its reduction.

Sea ice conditions and navigability through the Northeast Passage in the past 40 years based on remote-sensing data

Sea ice conditions and navigability along four typical routes of the Northeast Passage(NEP)are analysed using remote-sensing data from 1979 to 2019.The influence of air temperature(T_(air))and surface wind on the sea ice concentration(SIC)and the navigability of routes is determined.It is found that the annually averaged SICs of the different routes have decreased over the past 41 years.The fastest rate of decrease occurred in the Kara Sea(∼−1%per year),while the slowest rates of decrease occurred in the Laptev/East Siberian Sea(∼−0.42%per year).The number of navigable days for the Kara Sea has become∼1–2 months longer than the Laptev/East Siberian Sea route as a result.The effect of T_(air) on SIC,quantified byΔSIC/ΔT_(air) in the routes through the eastern Kara Sea and Laptev/East Siberian Sea in 2010s was∼−0.04/℃,two to three times that seen during the 1980s.Air temperature is becoming a significant driving force of melting ice in these routes.Surface winds are also a crucial factor for the navigability of the Vilkitsky Strait and Long Strait,as they drive ice drift,and affect the navigability of the Kara Strait by introducing warm air.

2014 summer Arctic sea ice thickness and concentration from shipborne observations

A series of shipborne sea ice observations were performed during the Chinese National Arctic Research Expedition in the Pacific Arctic sector between 2 August 2014 and 1 September 2014.Undeformed sea ice thickness(SIT)as well as area fractions of open water,melt pond,and sea ice(Aw,Ap,and Ai)were monitored using downward-oriented and oblique-oriented cameras.The results show that SIT varied between 20 and 220 cm throughout the whole cruise,with the average and standard deviation equaling 104.9 and 29.1 cm,respectively.Mean Aw and Ai were 0.52 and 0.44 in the marginal ice zone,respectively,while mean Aw decreased to 0.23 and mean Ai increased to 0.73 in the pack ice zone.Limited variation between 0 and 0.32 in Ap was seen throughout the whole cruise.Shipborne sea ice concentration was then rectified and mapped across a large transect to validate estimates derived from the satellite sensors Special Sensor Microwave Imager/Sounder(SSMIS)(25 km)and AMSR2(25 km).Overestimations were 9.5%and 9.9%for SSMIS and AMSR2 compared with measurements,respectively.The mean areal broadband surface albedo based on shipborne survey increased from 0.07 to 0.66 along the transect between 72°N and 81°N.

Simulation study on interaction coefficient of DEM in non-spherical large size (5-30 mm) coal particles

The pneumatic conveying system of coal particles can greatly reduce the dust and improve the environmental quality at underground mining workface and the surrounding of coal enterprises.The particle shape and the interaction coefficients between particles and the contact surface play important roles in the pneumatic conveying and CFD-DEM simulation.In order to build the semblable shape models and obtain the accurate interaction coefficients of large coal particles,this article establishes the con tact model by the particle overlap method and describes the mathematical model of the shape characteristics for large coal particle.The particle models are simulated by adopting the multi-index mixed orthogonal experiments.The accumulation density,the porosity and the error between simulation and experiment are taken as the indexes,and the particle models and the particle contact coefficients are taken as the orthogonal test factors.As a result,three more accurate particle models and their interaction coefficients are obtained,which provide the model basis for the pneumatic conveying of large coal particles.

Recent Progress on Organic Near-Infrared Photodetectors:Mechanism,Devices,and Applications

Comprehensive Summary Near infrared light organic photodetectors have attracted tremendous attention due to their tailorable response,ease of processing,compatibility with flexible substrate,room temperature operation and broad applications such as remote sensing,health monitoring,artificial vision,night vision,and so on.Recently,the great improvement obtained on the important figures of merit performances has made organic photodetectors catch up and even surpass those of inorganic photodetectors in some respects.In this review,after a brief illustration of the organic photodetectors'figures of merit performances,we summarize the research progress of panchromatic and narrowband near infrared light organic photodetectors from their working mechanism,strategies to achieve narrowband near infrared light organic photodetectors,to some practical applications.Finally,we discuss the development challenge of the near infrared light organic photodetectors.

Manipulating optical Tamm state in the terahertz frequency range with graphene

The optical Tamm state(OTS), which exists generally at the interface between metal and a dielectric Bragg mirror, has been studied extensively in the visible and near infrared spectra. Nevertheless, OTS in the terahertz(THz) region normally receives far less attention. In this Letter, we demonstrate the physical mechanism of OTS at the interface between graphene and a dielectric Bragg mirror in the THz frequency band by applying the transfer matrix method and dispersion characteristics. Based on such mechanisms, we propose an efficient method that can precisely generate and control OTS at a desired angle and frequency. Moreover, we show that the OTS is dependent on the optical conductivity of graphene, making the graphene–dielectric-Bragg-mirror a good candidate for dynamic tunable OTS device in the THz frequency range.