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111.
采用国标《碱性过硫酸钾消解紫外分光光度法》( HJ 636-2012)测定水中总氮( TN),虽然实验步骤简单,但影响因素较多,需严格控制实验条件。本文针对含量在方法检出限0.05 mg/L附近的微量总氮水样,从实验用水、器皿的处置、试剂的配制与存放、消解样品的制作与冷却时间等方面考察了总氮空白值的控制、校准曲线的选取等影响因素,优化了实验条件,结果令人满意。 相似文献
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113.
Revisiting Kappa to account for change in the accuracy assessment of land-use change models 总被引:7,自引:0,他引:7
Land-use change models are typically calibrated to reproduce known historic changes. Calibration results can then be assessed by comparing two datasets: the simulated land-use map and the actual land-use map at the same time. A common method for this is the Kappa statistic, which expresses the agreement between two categorical datasets corrected for the expected agreement. This expected agreement is based on a stochastic model of random allocation given the distribution of class sizes. However, when a model starts from an initial land-use map and makes changes to it, that stochastic model does not pose a meaningful reference level. This paper introduces KSimulation, a statistic that is identical in form to the Kappa statistic but instead applies a more appropriate stochastic model of random allocation of class transitions relative to the initial map. The new method is illustrated on a simple example and then the results of the Kappa statistic and KSimulation are compared using the results of a land-use model. It is found that only KSimulation truly tests models in their capacity to explain land-use changes over time, and unlike Kappa it does not inflate results for simulations where little change takes place over time. 相似文献
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115.
Evaluation of health impacts arising from inhalation of pollutant particles <10 μm (PM10) is an active research area. However, lack of exposure data at high spatial resolution impedes identification of causal associations between exposure and illness. Biomagnetic monitoring of PM10 deposited on tree leaves may provide a means of obtaining exposure data at high spatial resolution. To calculate ambient PM10 concentrations from leaf magnetic values, the relationship between the magnetic signal and total PM10 mass must be quantified, and the exposure time (via magnetic deposition velocity (MVd) calculations) known. Birches display higher MVd (∼5 cm−1) than lime trees (∼2 cm−1). Leaf saturation remanence values reached ‘equilibrium’ with ambient PM10 concentrations after ∼6 ‘dry’ days (<3 mm/day rainfall). Other co-located species displayed within-species consistency in MVd; robust inter-calibration can thus be achieved, enabling magnetic PM10 biomonitoring at unprecedented spatial resolution. 相似文献
116.
Weile Wang Kazuhito Ichii Hirofumi Hashimoto Andrew R. Michaelis Peter E. Thornton Beverly E. Law Ramakrishna R. Nemani 《Ecological modelling》2009
The increasing complexity of ecosystem models represents a major difficulty in tuning model parameters and analyzing simulated results. To address this problem, this study develops a hierarchical scheme that simplifies the Biome-BGC model into three functionally cascaded tiers and analyzes them sequentially. The first-tier model focuses on leaf-level ecophysiological processes; it simulates evapotranspiration and photosynthesis with prescribed leaf area index (LAI). The restriction on LAI is then lifted in the following two model tiers, which analyze how carbon and nitrogen is cycled at the whole-plant level (the second tier) and in all litter/soil pools (the third tier) to dynamically support the prescribed canopy. In particular, this study analyzes the steady state of these two model tiers by a set of equilibrium equations that are derived from Biome-BGC algorithms and are based on the principle of mass balance. Instead of spinning-up the model for thousands of climate years, these equations are able to estimate carbon/nitrogen stocks and fluxes of the target (steady-state) ecosystem directly from the results obtained by the first-tier model. The model hierarchy is examined with model experiments at four AmeriFlux sites. The results indicate that the proposed scheme can effectively calibrate Biome-BGC to simulate observed fluxes of evapotranspiration and photosynthesis; and the carbon/nitrogen stocks estimated by the equilibrium analysis approach are highly consistent with the results of model simulations. Therefore, the scheme developed in this study may serve as a practical guide to calibrate/analyze Biome-BGC; it also provides an efficient way to solve the problem of model spin-up, especially for applications over large regions. The same methodology may help analyze other similar ecosystem models as well. 相似文献
117.
根据FHD 1型质子磁力仪在实际使用过程中存在的一些问题 ,以及一些用户提出的建议和要求 ,对FHD 1型质子磁力仪的实时时钟、标定方法、通用性与适应性、抗干扰能力方面进行了改进和完善 ,本文对此作介绍。 相似文献
118.
M.F. Mylne 《Journal of the American Water Resources Association》1989,25(3):535-539
ABSTRACT: Near real time daily rainfall estimates for the UK are available from three sources: a sparse network of gauges, radar data, or radar data adjusted by the sparse gauges. The PARAGON rainfall archive system, which has been developed by the UK Meteorological Office, is able to produce these estimates in near real time on a 5 km grid. The ability of these estimates to reproduce the 5 km grid point field derived later from a dense network of gauges is compared using case studies. Five techniques have been used to assess the relative quality of the various estimates. There is general agreement between the results of the various techniques. For the London radar there are examples of days when the rainfall estimate was improved by incorporating radar data; conversely, there are days when the radar data make it worse. Overall little evidence was found to suggest that adjusted radar data are consistently markedly better than gauge estimates. Discriminate use of radar data is recommended. 相似文献
119.
为可靠测试基准镇流器的电压/电流比、功率因数,本文简要介绍了基准整流器的校准方法,对校准结果的不确定度评定进行了分析,给出了测量结果的不确定度,同时验证了该校准方法的可行性。 相似文献
120.
Richard G. Allen Boyd Burnett William Kramber Justin Huntington Jeppe Kjaersgaard Ayse Kilic Carlos Kelly Ricardo Trezza 《Journal of the American Water Resources Association》2013,49(3):563-576
A remaining challenge to applying satellite‐based energy‐balance algorithms for operational estimation of evapotranspiration (ET) is the calibration of the energy‐balance model. Customized calibration for each image date is generally required to overcome biases associated with radiometric accuracy of the image, uncertainties in aerodynamic features of the landscape, background thermal conditions, and model assumptions. The CIMEC process (calibration using inverse modeling at extreme conditions) is an endpoint calibration procedure where near extreme conditions in the image are identified where the ET can be estimated and assigned. In the Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC?) energy‐balance model, two endpoints represent the dry and wet ends of the ET spectrum. Generally, user‐intervention is required to select locations in the image to produce best accuracy. To bring the METRIC and similar processes into the domain of less experienced operators, a consistent, reproducible, and dependable statistics‐based procedure is introduced where relationships between vegetation amount and surface temperature are used to identify a subpopulation of locations (pixels) in an image that may best represent the calibration endpoints. This article describes the background and logic for the statistical approach, how the statistics were developed, area of interest requirements and assumptions, adjustment for dry conditions in desert climates, and implementation in a common image processing environment (ERDAS Imagine). 相似文献