Cascade multitemporal classification based on fuzzy Markov chains     

Raul Q. Feitosa  Gilson A.O.P. Costa  Guilherme L.A. Mota  Kian Pakzad  Maria C.O. Costa 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(2):159-170

This paper proposes a new fuzzy cascade multitemporal classification method based on Fuzzy Markov Chains. This method differs from prior fuzzy multitemporal approaches proposed thus far, as the method does not require the knowledge of the true class at an earlier date; instead it uses the attributes of the image object being classified at the earlier date. This method combines the fuzzy, non-temporal, classification of a geographical region at two points in time to provide a single unified result. A transformation law based on class transition possibilities projects the earlier classification onto the later date before combining both results. Performance analysis was conducted upon a sequence of three LANDSAT images from the central region of Brazil using a Genetic Algorithm to estimate transition possibilities. The analysis showed that the increase in performance is highly dependent on whether or not a significant correlation exists between the temporal data sets, as well as on the accuracy of the monotemporal classifier at the earlier date. While the monotemporal approach used in the experiments attained an average class accuracy of approximately 55%, the multitemporal scheme achieved between 65% and 95%. Similar results in terms of overall accuracy were also observed. Furthermore, compared to two alternative cascade multitemporal classification approaches, the proposed method consistently showed better results.  相似文献   

Metallogeny of the Lannigou Sedimentary Rock-hosted Disseminated Gold Deposit in Southwestern Guizhou Province, China     

BAO Zhiwei Jayanta GUHA 《《地质学报》英文版》2007,81(1):121-134

The Lannigou deposit is a large-sized sedimentary rock-hosted disseminated gold （SRHDG） deposit located in the Youjiang Basin. It is hosted by the Middle Triassic turbidite. Wall rock alterations, including silicification, pyritization, arsenopyritization, carbonatization and argillization, commonly occur along fractures. PGE study demonstrates that either Permian basalts or Triassic ultrabasic intrnsives are unlikely to be the main source of gold mineralization. Coupled with the lack of other nmgmatic activity in the vicinity of the mining area, an amagmatic origin is proposed. Organic matter compositions and GC-MS analysis of the ores and host rocks show that the organics in the ores and the host rocks have a common source; the organic matter in the ores was mainly indigenous. The positive correlation between S2 and Au contents, along with the common occurrence of organic inclusions, suggest involvement of organic matter in the ore-forming process in terms of promoting Au leaching from the source rocks, making colloidal Au migration possible, as well as hydrocarbon reduction of sulphate. Geological and geochemical characteristics of the Lannigou deposit suggest that it was formed through circulation of meteoric water and probably less importantly organic bearing formation water driven by high geothermal gradient caused by late Yanshanian extension, which leached Au from the source bed, and then migrated as Au-bisnlfides and colloidal Au, culminating in deposition by reduction-adsorption and surface complexation of gold onto the growth surface of arsenlan pyrite.  相似文献   

Short-term and diurnal temperature changes alter the response of harmful algal blooms of Pseudo-nitzschia pungens to solar ultraviolet radiation     

J. Chen  H. Wang  A. Q. Yang  R. R. Si 《新西兰海洋与淡水研究杂志》2018,52(1):69-81

In this study, we explored the interactive effects of temperature and solar ultraviolet radiation (UVR) on the growth, pigment contents, photochemical efficiency and non-photochemical quenching (NPQ) of Pseudo-nitzschia pungens, which forms harmful algal blooms globally. Cells were first pre-acclimated to temperatures of 20°C, 25°C or 28°C for 10 days. They were then exposed to three different types of solar radiation for 60?min. We then measured the photochemical efficiency of the cells during the 60-min exposure and a 360-min recovery period under dim light (20?μmol?photons?m^?2?s^?1). In addition, we analysed the diural change in photochemical efficiency and NPQ over a 10-h period. We found that P. pungens that were exposed to higher temperatures in the short term (i.e. 20–25°C, 20–28°C and 25–28°C) or long term (i.e. 25–25°C and 28–28°C) exhibited lower levels of photoinhibition and faster recovery rates than samples exposed to a lower temperature (i.e. 20–20°C). This indicated that the deleterious effects of UVR can be minimised by both chronic and acute exposure to higher temperatures within the tolerated temperature range for P. pungens.  相似文献   

Polarization properties of low frequency electromagnetic cyclotron waves associated with magnetic clouds     

G. Q. Zhao  H. Q. Feng  D. J. Wu  J. Huang 《Astrophysics and Space Science》2018,363(3):49

Recent studies have revealed that there are a large number of low frequency electromagnetic cyclotron waves (ECWs) occurring in and around magnetic clouds (MCs) that are common magnetic structures in interplanetary space. Using magnetic field data from the STEREO spacecraft, this paper investigates polarization properties of ECWs associated with 120 MCs. Results show that the ECWs are highly transverse, strongly polarized waves with large ellipticities. Specifically, almost all of the waves take place with the ratios of transverse power to total power higher than 0.94, polarization degrees greater than 0.85, and ellipticities larger than 0.5. The mean values of these quantities can be up to 0.99, 0.96, 0.85, respectively. In particular, there is a tendency of ellipticities decreasing with respect to the wave normal angles for ECWs with left handed polarization. The decreasing tendency is consistent with the recent theory and simulation results.  相似文献   

Editorial     

D.Q. Bowen 《Quaternary Science Reviews》1990,9(4)

  相似文献   

出乎意料的火星温度     

Charles Q Choi  胡德良 《海洋地质前沿》2008,24(7):42-42

日前,对火星北极冰层以下的探测显示：这颗红色星球的温度可能远远低于过去的估计。因此研究人员提出,火星上可能存在的液态水或许是深藏不露,出乎预料,其位置离火星温暖的核心部位更近。  相似文献   

Pleistocene deposits at Stoke Goldington,in the valley of the Great Ouse,UK     

C. P. Green  G. R. Coope  R. L. Jones  D. H. Keen  D. Q. Bowen  A. P. Currant  D. T. Holyoak  M. Ivanovich  J. E. Robinson  R. J. Rogerson  R. C. Young 《第四纪科学杂志》1996,11(1):59-87

At Stoke Goldington in the valley of the Great Ouse in Buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late Middle Pleistocene. Near the base of the succession, at a level only 1 m above the modern floodplain, a fossil assemblage, including pollen, plant macrofossils, molluscs, insects and ostracods, provides evidence for the local development of herb-rich grassland under temperate climatic conditions. The fossil record, amino-acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during Oxygen Isotope Stage 7. The deposits containing the temperate assemblage are immediately overlain by typical cold-climate gravels of the Great Ouse. These have been subjected to a later cut-and-fill episode, with the fill accumulating in cool climatic conditions. The cut-and-fill episode was succeeded by aggradation, forming the overlying terrace surface. Amino-acid racemisation ratios indicate that the fill was emplaced, and the terrace surface created, during or after Oxygen Isotope Stage 5. © 1996 John Wiley & Sons, Ltd.  相似文献   

Impact of forest degradation on streamflow regime and runoff response to rainfall in the Garhwal Himalaya,Northwest India     

Nuzhat Q. Qazi  L. Adrian Bruijnzeel  Shive Prakash Rai  Chandra P. Ghimire 《水文科学杂志》2017,62(7):1114-1130

Baseflows have declined for decades in the Lesser Himalaya but the causes are still debated. This paper compares variations in streamflow response over three years for two similar headwater catchments in northwest India with largely undisturbed (Arnigad) and highly degraded (Bansigad) oak forest. Hydrograph analysis suggested no catchment leakage, thereby allowing meaningful comparisons. The mean annual runoff coefficient for Arnigad was 54% (range 44–61%) against 62% (53–69%) at Bansigad. Despite greater total runoff Q_t (by 250 mm year^–1), baseflow at Bansigad ceased by March, but was perennial at Arnigad (making up 90% of Q_t vs. 51% at Bansigad). Arnigad storm flows, Q_s, were modest (8–11% of Q_t) and occurred mostly during monsoons (78–98%), while Q_s at Bansigad was 49% of Q_t and occurred also during post-monsoon seasons. Our results underscore the importance of maintaining soil water retention capacity after forest removal to maintain baseflow levels.