Passive microwave observations of vegetation water content (VWC) are important to monitor vegetation growth status and terrestrial aboveground biomass. To constrain the L-band Microwave Emission of the Biosphere (L-ME...
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Passive microwave observations of vegetation water content (VWC) are important to monitor vegetation growth status and terrestrial aboveground biomass. To constrain the L-band Microwave Emission of the Biosphere (L-MEB) model for NASA’s Soil Moisture Active Passive (SMAP) satellite mission, vegetation structure parameter b is often used to estimate VWC from the climatological Normalized Difference Vegetation Index (NDVI). However, little is known about what and how the driving factors impact the parameter b and its modeling due to the lack of quantitative analysis. Based on the Passive Active L-band Sensor (PALS) data from the SMAPVEX16-MB campaign, this study firstly calibrated the parameter b for canola, wheat and soybean. Afterwards, a Random Forest algorithm was employed to model b-values using both h and v polarized observations with the input features screened by correlation analysis and stepwise regression for each vegetation type, the R2 of which exceeds 82%. Considering the poor interpretability of machine learning algorithms, we also employed multivariable-linear regression to quantify their influence on b-values and achieved an R2 exceeding 75%. The results showed all three crop types had an increasing trend in b-values at dual-polarization with their growth, except for wheat which exhibited a decreasing trend at v-polarization. Among the three crops, wheat and soybean indicated sharp changes in b-values, particularly during the late growth stage, while canola exhibited slower changes. The b-values were higher at v-polarization than at h-polarization, except for wheat during the early growth stage and at the end of the late growth stage. The results of multivariable regression with vegetation type as dummy variables (soybean as the control) indicated that crop type significantly affected b values, with canola and wheat exhibiting positive effects on b-values at h-polarization but negative effects at v-polarization. Additionally, we found that VWC, biomass
作者：
丁一汇李崇银柳艳菊National Climate Center
China Meteorological Administration Beijing 100081 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics
Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 National Climate Center
China Meteorological Administration Beijing 100081 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid DynamicsInstitute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029he present paper gives an overview of the key project " South China Sea Monsoon Experiment (SCSMEX)" operated by the Ministry of Science and Technology of China during the period of 1996-2001. The SCSMEX is a joint atmospheric and oceanic field experiment which aims to better understand the onset maintenance and variability of the summer monsoon over the South China Sea (SCS). It is a large-scale international effort with many participating countries and regions cooperatively involved in this experiment. With the field observation in May-August 1998 a large amount of meteorological and oceanic data was acquired which provides excellent datasets for the study of the SCS monsoon and the East Asian monsoon and their interaction with the ocean. The preliminary research achievements are as follows. (1) The earliest onset of the Asian monsoon over the SCS and Indo-China Peninsula has been well documented. Prom the viewpoint of the synoptic process its onset is closely related to the early rapid development of a twin cyclone to the east of Sri Lanka. The conceptual modei of the SCS monsoon onset in 1998 was put forward. The 50-year time series of the SCS monsoon onset date was also made. (2) Two major modes namely the 30-60-day and 10-20-day oscillations were ascertained. The influences of the abnormal SCS monsoon on the precipitation over eastern China and its modes were identifled. A strong (weak) monsoon over the SCS usually leads to less (more) precipitation over the middle and lower reaches of the Yangtze River
The present paper gives an overview of the key project ' South China Sea Monsoon Experiment (SCSMEX)' operated by the Ministry of Science and Technology of China during the period of 1996-2001. The SCSMEX is a...
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The present paper gives an overview of the key project ' South China Sea Monsoon Experiment (SCSMEX)' operated by the Ministry of Science and Technology of China during the period of 1996-2001. The SCSMEX is a joint atmospheric and oceanic field experiment which aims to better understand the onset, maintenance, and variability of the summer monsoon over the South China Sea (SCS). It is a large-scale international effort with many participating countries and regions cooperatively involved in this experiment. With the field observation in May-August 1998, a large amount of meteorological and oceanic data was acquired, which provides excellent datasets for the study of the SCS monsoon and the East Asian monsoon and their interaction with the ocean. The preliminary research achievements are as follows. (1) The earliest onset of the Asian monsoon over the SCS and Indo-China Peninsula has been well documented. Prom the viewpoint of the synoptic process, its onset is closely related to the early rapid development of a twin cyclone to the east of Sri Lanka. The conceptual modei of the SCS monsoon onset in 1998 was put forward. The 50-year time series of the SCS monsoon onset date was also made. (2) Two major modes, namely the 30-60-day and 10-20-day oscillations were ascertained. The influences of the abnormal SCS monsoon on the precipitation over eastern China and its modes were identifled. A strong (weak) monsoon over the SCS usually leads to less (more) precipitation over the middle and lower reaches of the Yangtze River basin, and more (less) precipitation in North China. (3) During the monsoon onset over the SCS, a wide variety of organized mesoscale convective systems (MCSs) were observed by a Doppler radar array deployed over the northern SCS. The relationship between large-scale circulations and MCSs during the monsoon onset process in 1998 was clearly revealed. It was suggested that there is a kind of positive feedback mechanism between large-scale circulations and
The S-wave $\bar{q}q\bar{s}Q \;\; (q=u,\,d;\,Q=c,\,b)$ tetraquarks, with spin-parities $J^P=0^+$, $1^+$, and $2^+$, in both isoscalar and isovector sectors, are systematically studied using a chiral quark model. The
The S-wave $\bar{q}q\bar{s}Q \;\; (q=u,\,d;\,Q=c,\,b)$ tetraquarks, with spin-parities $J^P=0^+$, $1^+$, and $2^+$, in both isoscalar and isovector sectors, are systematically studied using a chiral quark model. The
The production of ammonia (NH 3 ) from nitrogen sources involves competitive adsorption of different intermediates and multiple electron and proton transfers, presenting grand challenges in catalyst design. In nature ...
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The production of ammonia (NH 3 ) from nitrogen sources involves competitive adsorption of different intermediates and multiple electron and proton transfers, presenting grand challenges in catalyst design. In nature nitrogenases reduce dinitrogen to NH 3 using two component proteins, in which electrons and protons are delivered from Fe protein to the active site in MoFe protein for transfer to the bound N 2 . We draw inspiration from this structural enzymology, and design a two-component metal–sulfur–carbon (M−S−C) catalyst composed of sulfur-doped carbon-supported ruthenium (Ru) single atoms (SAs) and nanoparticles (NPs) for the electrochemical reduction of nitrate (NO 3 − ) to NH 3 . The catalyst demonstrates a remarkable NH 3 yield rate of ~37 mg L −1 h −1 and a Faradaic efficiency of ~97 % for over 200 hours, outperforming those consisting solely of SAs or NPs, and even surpassing most reported electrocatalysts. Our experimental and theoretical investigations reveal the critical role of Ru SAs with the coordination of S in promoting the formation of the HONO intermediate and the subsequent reduction reaction over the NP-surface nearby. Such process results in a more energetically accessible pathway for NO 3 − reduction on Ru NPs co-existing with SAs. This study proves a better understanding of how M−S−Cs act as a synthetic nitrogenase mimic during ammonia synthesis, and contributes to the future mechanism-based catalyst design.
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