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By J. W. van der Merwe, A. S. Bolokang, M. J. Phasha, V. J. Matjeke, C. Moopanar

"Excessive wear rates on railway wheels can result in rolling-stock derailments. If wear is detected early the possible derailments can be prevented by prematurely replacing wheelsets, although the inventory cost and maintenance downtime remain a challenge. In the current study, wheels were introduced and monitored in-service for two years to investigate the cause of excessive wear rates. The wear rates and stresses were calculated for the wheels suitable for a maximum load of 26 t per axle. Microstructural and mechanical properties were analysed. As expected, the general microstructure of all the wheels tested was pearlitic. Although all the wheels complied with the tensile strength requirements, stress calculations confirmed material distortion on excessively worn wheels whereas trial wheels revealed yield strength exceeding the yield criterion. High wear rates observed on the wheels were a result of low yield strength relative to the load per axle. The typical wear mechanism found was due to a combination of rolling contact fatigue and abrasive brake wear. Despite compliance of the wheels with existing requirements regarding material and mechanical properties (hardness, ultimate tensile strength), it is recommended that the yield strength must also be taken into consideration as a critical parameter.IntroductionRailway wheels are used to support the wagon mass and guide the wagon along the tracks (Park, 1974). The wheels and rails must be able to tolerate the applied tangential forces in order to effect wagon dynamic performance and reduce material deformation (Ghidini et al., 1994; RSE_TE_SPC_0045, 2011; AAR M107/M 208 Specification, 2011. Over the past ten years, the South African coal wagon maintenance depot has experienced excessive hollow wheel wear rates on the heavy haul line wheels. The maximum load of Jumbo wagons on the coal line is 104 t, or 26 t per axle. Although the maintenance intervention cycle for wheelsets was two years, between February 2011 and August 2012 some wheels experienced excessive hollow wear. Hollow wear is regarded as wear exceeding 2 mm on the central portion of the wheel tread (RSE_TE_SPC_0045, 2011). This happened despite the fact that these wheels were manufactured and certified according to the requirements of AAR M107/208 standard for carbon steel wheels (AAR M107/M 208 Specification,. 2011) and the local wheel RS/ME/SP 021 standard specification (RS / ME / SP / 021 REV 5 (2013). The AAR standard only specifies a minimum hardness as a required mechanical property and the local standard specifies hardness and minimum tensile strength only. In general, an increase in hardness will improve the rolling/sliding wear resistance of steel. This relationship of hardness and wear resistance was found to be true only in a situation where solid and similar alloys are in contact (Singh, Khatirkar and Sapate, 2015). The sliding wear resistance of a material is usually estimated using Archard’s equation (Liu and Li, 2001)."

Jan 1, 2016

By D. F. Zhang, X. Q. Jiang, N. Tahreen, D. L. Chen, F. S. Pan, D. Y. Li

Alloying with rare-earth elements has been proven to be an important tool for magnesium to achieve superior properties via texture randomization. The role of yttrium in texture weakening and the link between texture and formability are fairly well known. Since annealing is a vital part of metal processing which could significantly contribute to ductility, it is important to ascertain the impact of annealing in terms of texture change. Also, an understanding about texture development during pre- and post-deformation annealing is essential to improve the industrial deformation processing as texture is closely related to formability. While there is independent information in the literature regarding the effect of rare-earth addition and heat treatment on the texture formation, no systematic studies have been reported on the collective impact of yttrium addition, annealing and deformation on texture evolution. The present study was, therefore, aimed to identify the inter-relationship among texture evolution, yttrium content, heat treatment and deformation behavior in an extruded Mg-Zn-Mn-Y alloy. Annealing at 450°C for 1 hour and uniaxial compression tests at a certain amount of deformation were performed. The deformed and annealed samples were then subjected to annealing and compression test, respectively, followed by texture measurements. It was observed that yttrium addition effectively weakened the crystallographic texture in all conditions, which was evident from the changes in the microstructures and textures.

Jan 1, 2015

By Roe-Hoan Yoon, Kaiwu Huang

Derjaguin and Dukhin [1] were the first to develop a first-principle flotation model by considering the role of surface forces in bubble-particle interactions. According to the model, the ζ-potentials of particles constitute the energy barriers, E12, for particle (1)-bubble (2) interactions, which corroborates well with the observation that flotation recoveries reach maxima under conditions of zero-zeta potentials. In the present work, a series of surface force measurements were conducted for the quartz-dodecylamine hydrochloride (DAH) flotation system, for which detailed studies had been conducted by D.W. Fuerstenau [2], including the measurements of zeta-potentials, contact angles and collector adsorption as a function of pH.

By Shigem Kuramoto

Pure copper is known to exhibit intermediate temperature embrittlement when it is deformed at a slow strain rate, and a small addition of zinc suppresses this embrittlement. In the present study, the relation between zinc addition and hydrogen behavior was taken into account since the impurity hydrogen is believed to deteriorate the ductility at intermediate temperatures. Pure copper and Cu-l mass % Zn alloy specimens are prepared by melting in argon and in vacuum, so that a comparison can be made between the specimens with normal hydrogen content and those with' less hydrogen content. Tensile tests are performed at temperatures ranging from room temperature to 600 "C, and hydrogen behavior is analyzed using a newly developed testing machine that can detect gas evolution from the specimens during deformation and fracture in ultra high vacuum. The small addition of zinc to pure copper decreases hydrogen content, leading to the improved ductility at intermediate temperatures. In addition, the samples of both pure copper and Cu-1%Zn melted in vacuum exhibited higher ductility at intermediate temperatures than those melted in argon atmosphere, which is attributed to reduced hydrogen content.

Jan 1, 1998

By Jr. Langhans, J. S. McPartland

"The presence of zinc in cyanide solutions is generally thought to not have an adverse effect on precious metal recovery or recovery rate by heap leach processing. However, analytical interferences of zinc in solution can cause problems in accurately determining and controlling cyanide concentration in the leach solution, leading to increased cyanide consumption. Analytical methods and the chemistry of cyanide in the presence of zinc are reviewed. The effects of solution pH and zinc concentration on the free cyanide determination were evaluated in detail. Use of the standard silver nitrate titration and a modified titration method for controlling cyanide concentration during heap leaching were investigated experimentally. The practical implications of cyanide heap leaching in the presence of cyanide soluble zinc minerals are discussed.IntroductionThe presence of zinc in precious metal cyanidation circuits is not uncommon. Zinc can be introduced into cyanide leach solutions through dissolution of various zinc minerals1>, or through the use of a Merrill Crowe (zinc precipitation) circuit. Zinc minerals typically occur infrequently and in low concentration in gold ores, but are more abundant in silver ores. Merrill Crowe systems are most commonly employed for recovery of precious metals from solution for relatively high silver ores. It is desirable to control the amount of dissolved zinc in a cyanidation circuit for several reasons. Excessive zinc build-up in cyanide leach solution can, under certain circumstances, inhibit precious metal dissolution and adversely affect solution recovery systems. Additionally, high zinc concentrations can lead to excessive in-process cyanide inventories and potentially, to higher cyanide consumption"

Jan 1, 1999

By Horace Mann

A FEW years ago, it was generally thought that from 15 to 18 per, cent. of zinc oxide was the upper limit of a workable lead blast-furnace slag. With slags above this zinc-oxide content, the furnaces gave so much trouble because of hearth, wall, and crucible accretions that the campaign was very short. The time lost in cleaning out the frozen furnaces, for it was seldom possible to blow them out, and blowing in was so great that it was considered uneconomical to attempt the running of high-zinc slags, even if this were metallurgically possible. It is true that there are, references to one or two slags much higher in zinc than the foregoing,1 but the average smelterman regarded these, as freaks and not to be considered for regular furnace work. One or two plants, notably the plant of the United States Smelting Co, at Canyon City, Colo., ran charges, higher in zinc. At this plant, the zinc-oxide content of the charge was frequently 20 per cent. and higher but the slags from these furnace's seldom ran over 10 to 12 per. cent. zinc oxide. The furnaces were run with a large volume of air under a relatively low pressure, a low smelting column, and a very hot top; as a result, a large amount of zinc was volatilized. Even with the low smelting column and hot top, accretions caused much trouble and barring, down was a daily occurrence. At the time most of the theories on lead blast-furnace work were promulgated or worked out, it was necessary to run a furnace with a cold top in order to avoid an excessive loss due to fines and fume. At the same time, the smelting conditions had to be such that the lead and silver would be reduced and would enter the bullion. The slag had to be liquid but the charge must not give excessive accretions either in the hearth or on the walls of the furnace. This forced the operators to run the furnaces with a comparatively low blast, which, in turn, caused a small fuel consumption per unit of time with the accompanying result of a low working temperature.

Jan 8, 1925

By D. He, A. Yaacoubi, A. Baçaoui, K. Boujounoui, A. Abidi, K. El Amari

The effects of utilizing recycled tailings pond water from the flotation plant at the Mining Company of Guemassa (MCG) on galena recovery and selectivity towards chalcopyrite (RPb-Cu) , sphalerite (RPb- Zn), and pyrrhotite (RPb-Fe) were studied at bench scale. The results showed that recycling the tailings pond water in the lead circuit without addition of fresh water gave a good flotation performance in terms of lead recovery (Rpb) (75%) and selectivity towards the other metals: RPb-Cu (54%), RPb-Zn (60%) and RPb-Fe(65%). This allows the water to be recycled at least four times. However, increasing the d80 from 100 μm to 160 μm currently used at the MCG plant had a negative effect on the lead flotation performance.

Nov 30, 2022

By Alexander Field

The hot-rolling properties of a series of high-sulfur steels are described. From a consideration of the sulfur, manganese, and zirconium contents of these steels, it is shown that zirconium reacts with the sulfur content of molten steel in accordance with the equation Zr + 2S = ZrS2. Zirconium disulfide appears in the finished state as gray-colored inclusions, similar to manganese sulfide in plastic behavior and general appearance. Zirconium completes its act of deoxidation before proceeding to combine with sulfur and indirectly increases the effective sulfur-combining power of any manganese which may be present. IN A previous paper,1 the experimental methods used and some of the results obtained in an extensive investigation of steels containing zirconium were described. The present paper considers in greater detail one of the most interesting of these effects, namely, the elimination of "red shortness" and the occurrence in steel of a compound of zirconium and sulfur. A consideration of the actual percentages of zirconium, manganese, and sulfur in numerous steels in the light of behavior during rolling has led to new conclusions of the most practical import regarding the reciprocal relationships of these elements. The microscopic examination of high-sulfur steels containing zirconium has also been productive of interesting results. Before discussing the experimental data in question, it may be stated, briefly, that the reaction between zirconium and sulfur in molten steel may he represented by the simple equation, Zr + 2S = ZrS2, and that the zirconium sulfide thus formed occurs in the finished steel in the form of gray-colored inclusions, closely resembling manganese sulfide and, like the latter, exhibiting plasticity at rolling temperatures. Molten steel containing zirconium retains such a negligibly small amount of oxygen in solution that the foregoing reaction goes to completion.

Jan 2, 1924

By F. C. Newton

REFINERS of lead by the Parkes process have always been solicitous of recovering the zinc used in the desilverization, and justly so, as the loss in zinc constitutes one of the heavy costs in this method of refining. Part of this loss is due to the absorption of zinc by lead, and in the present state of knowledge is not recoverable as metallic zinc. The remainder of the zinc, which finds its way into the precious-metal-bearing crust, is recoverable and naturally engages the operators' most exacting attention. Careful elimination of the impurities in base bullion has enabled the refiner to produce a zinc crust better adapted to retorting, which reflects favorably in the zinc recovery; and to produce a richer crust, thereby lowering the zincking cost, as the increased efficiency of the zinc results in less of it being in circulation. It is obvious that if the ratio of concentration be increased, a lessening of the amount of crust formed will ensue, throwing less work on the retorts and diminishing the amount of retort metal sent to the cupels, thus making an actual money saving in all these operations. In the effort to obtain a rich crust, the metallurgist has increased the heat to a considerable degree, upon the assumption that at the higher temperature the zinc-silver alloy could be squeezed free from the adhering lead. A further possibility for improvement suggested itself in the freezing-point curve of Prof. H. C. Carpenter, upon zinc and silver. Study of this curve disclosed the existence of a definite chemical compound, . Zn3Ag2, with a freezing point of 665° C., a promising compound for practical application.

Jan 2, 1915

Discussion of the paper of F. C. NEWTON, presented at the New York meeting, Feb-ruary, 1915, and printed in Bulletin No. 9S, February, 1915, pp. 473 to 477. H. 0. HOFMAN, Boston, Mass.-The results of these large-scale experiments, which were carried on at Perth Amboy, show that there are many differences between theoretical conceptions and their applications to work on a large scale. The author has given reasons why the results of bringing a desilverizing kettle to the high melting point of the zinc-silver alloy, Zn3Ag2, melting at 665° C., are not satisfactory. In all probability the alloy is dissolved in the lead; it may also be decomposed by the lead; the practical result is that this high temperature does not work. It remains now for the laboratory man to carry on systematic experiments

Jan 5, 1915

By C. M. Acuña

Copper losses in slags are of great concern, specially in smelting and slag cleaning processes. It is widely accepted that the suspension of metallic copper and matte droplets is strongly affected by the viscosity of the slag. The Chuquicamata Division of Codelco- Chile produces concentrates high in zinc, an element which reports mainly to the slag phase. The ZnO may affect the viscosity and therefore the copper losses. This work aimed to investigate the effect of lime to control the viscosity of slags, and in turn to control the copper losses. By using the experimental viscosity data and the Stoke's law, the settling rate of matte prills in various slags was estimated. The results indicate the possibility of increasing the recovery of copper and/or decrease the process time.

Jan 1, 1999

By Z. Zhang, X. -G. Chen, F. Breton, A. Arici

"The microstructure of Al-10Si-0.3Mg-0.5Mn alloy with 0.27% Zr and 0.19% V addition was quantitatively analysed and compared to the base material. The addition of Zr and V in the AlSi10Mg alloy exhibit a beneficial effect on the Si modification, resulting in the reduction of the size of eutectic Si particles on both as-cast and T6 conditions. The quantitative image analysis results show that the Zr and V addition and T6 treatment can reduce the size of the intermetallic phases. In addition, the presence of Zr and V is favour to the partial dissolution of the intermetallic phases during the T6 treatment. Different heat treatment procedures were tested to optimize treatment parameters. The mechanical properties of the alloys were evaluated using hardness measurements and tensile tests. The results show that the addition of Zr and V can remarkably improve the mechanical properties on as-cast and T6-treated conditions. The correlation between the microstructure and mechanical properties of the alloys is discussed.INTRODUCTION Al-Si-Mg foundry alloys have been widely used in automotive and aerospace industries due to their high strength-to-weight ratio, heat-treatable capability and excellent castability. The alloying elements such as Cu, Mn, Fe are traditionally added into Al-Si-Mg alloys to improve their mechanical properties (Mohamed, Samuel, Samuel & Doty, 2009). In recent years, the attention has been paid to the effect of the transition elements such as Zr, V, Ti, etc, as minor alloying additives, on the properties of aluminum alloys (Elhadari, Patel, Chen, & Kasprzak, 2011; Kasprzak, Amirkhiz & Niewczas, 2014; Shaha, Czerwinski, Kasprzak, Friedman & Chen, 2015; Shaha, Czerwinski, Kasprzak & Chen, 2014; Mahmudi, Sepehrband, Ghasemi & 2006; Meng, Cui, Zhao & Zuo, 2013). Kasprzak et al., (2014) and Shaha et al., (2015) reported that additions of Zr, V, and Ti in Al-Si-Cu-Mg cast alloys can improve the alloy mechanical properties at high temperature by forming stable intermetallics and precipitates on as-cast and heat treatment conditions. On the other hand, the mechanical properties of near-eutectic and eutectic Al–Si cast alloys depend not only on the chemical composition but also, even more importantly, on microstructural features such as the morphology and size of eutectic silicon and intermetallic particles, which are present on both as-cast and heat treatment conditions (Mohamed et al., 2009). However, there is rather limited information on the effect of Zr and V on the microstructure features and mechanical properties of near-eutectic Al-Si-Mg cast alloys."

Jan 1, 2018

By Roe-Hoan Yoon, Kaiwu Huang

Derjaguin and Dukhin (1961) were the first to develop a model for bubble-particle interaction in flotation from first principles by considering the surface forces in wetting (or flotation) films. The model predicted that the energy barriers to bubble-particle attachment arise from the ζ-potentials of fine particles, which corroborates well with an earlier work of Fuerstenau (1957) reported for the flotation of quartz using dodecyl ammonium acetate (DAA) as collector. In the present work, a series of surface force measurements have been conducted by accurately monitoring the changes in bubble curvature during bubble-silica surface interactions. The curvature changes are then used to determine the capillary force, which is the sum of the hydrodynamic and surface forces. By subtracting the former that can also be determined from the curvature changes, one obtains the surface forces (or disjoining pressure). The results obtained as functions of pH and collector concentrations show that control of the ζ-potentials of bubbles relative to those of the silica surfaces is critical for maximizing the negative disjoining pressure, which is conducive to promoting bubble-particle attachment in flotation.

By C. E. Wood

THIS paper is a brief report of experimental work undertaken to determine whether barium oxide in any quantity increases the desulfurizing action of blast-furnace slags. Industrial furnace operation with slag containing small quantities of barium oxide, referred to later, interested S. A. Sanford of the Commercial Chemical Co., Youngstown, Ohio, to conduct experiments to furnish comparative results on desulfurization with normal slag and slag containing small quantities of barium oxide. The U. S. Bureau of Mines agreed to assist on the problem because of the possible saving in fuel if the desulfurizing action of blast-furnace slag can be substantially increased, also because the experiments would yield new information on sulfur elimination in general, a matter of economic importance in furnace practice. A more complete and fundamental study of desulfurization of iron by slag is in progress.

Jan 1, 1929

By E. Steiakakis, A. Athousaki

Nowadays, stakeholders have a strong say to the enforcement of best practices by mining and quarrying companies. In most cases there is a direct relationship between sustainable development principles and best practices. Mining companies try to apply best practices in order to sustain their operation without lost time and effort to litigation, and other obstacles. However, when and where there is a lack of state or regional mineral policy, or when the mineral policy is fragmented and touching on conflicting laws, mining operations may be subject to additional administrative hassles, and, thus, operators feel threatened and tend to apply best practices loosely. This paper argues that the only way that mining and minerals operations can be a source of development is to ensure that they are working within the framework of sustainable development. Furthermore, in order to follow the paradigm of sustainable development they would need to be guided by a regional, national or even transnational (i.e. European) minerals policy.

Jan 1, 2011

By Wallace Thorneycroft

FOREWORD This paper by Mr. Thorneycroft, Past President of the Institution of Mining Engineers (Great Britain), and chairman of its Subsidence Committee, is a valuable contribution to the assemblage of data on ground movement and subsidence from coal mining. It deals with the effects of advancing longwall, a method almost universal in Europe but as vet little used in the United States outside of Northern Illinois and in a few scattered places elsewhere, in thin coal beds, as in the Lexington field, Missouri, Canon City field, Colorado, and the Birmingham field, Alabama. Although by advancing- longwall, a maximum recovery of coal is obtained and it has to be employed where there are weak shale roofs, especially in deep mines, it is a more expensive method of operation unless the mining conditions are favorable, which is unusual in the United States. On the other hand, there is a growing use in this country of what is essentially retreating long wall, with an approximately straight break-line as described by Rayburn.1 With this method, in which the pillars are substantial, it was shown that the ground movement effect is practically identical with that of advancing longwall, hence the value to mining engineers of the precise data given by Mr. Thorneycroft. His study is unusual in several respects; it deals with conditions connected with ,the mining of a coal bed 20 in. thick, about 490 ft. below the surface, over a mined-out area in a 5-ft. bed about 90 ft. below, which had been mined about 12 years earlier. Both mines passed under Plean House, a building of massive cut stone construction built over a century ago, in which Mr: Thorneycroft resided throughout the under-mining period. Slight cracks opened in the walls as the longwall face approached the house in mining the upper seam, and closed after the face passed and subsidence took place. In the northwest wall, the last wall the face passed under, some stone blocks were broken, which was attributed to a strike period when the advance of face came nearly to a standstill. Other than this there was no perceptible permanent damage, as indicated by the photographs taken by the undersigned in 1923 (Figs. 1 and 2). Mr. Thorneycroft used a novel means of studying the successive positions of the corners of the building: he hung plumb bobs from the eaves and traced the paths of the respective plumb bob points on level surfaces. The angles made by the house walls with the plumb bob lines gave measures of the slope of the subsidence wave at the respective points. A slight upward wave was indicated by the surveys ahead of the subsidence, which would appear to be due to a tilting over of the massive sandstone stratum in the roof measures near the surface, the edge of the subsidence area acting as the fulcrum.

Jan 1, 1931

By T. C. Wilson, Gerald Edmunds, W. M. Peirce, E. A. Anderson

Thirty-six elements have been alloyed singly with cartridge brass. Ammonia and mercury stress-cracking tests have been conducted on the as-rolled and recrystallized strip. Ultra high purity cartridge brass has also been tested. Silicon improves stress- cracking behavior. High silicon (I per cent) cartridge brass quenched from high temperature (for example, 800 C.) annealing is exceptionally resistant to ammonia stress cracking. This improvement is not lost by subsequent cold working, but is greatly reduced by subsequent low temperature annealing. Phosphorus, arsenic, barium, cerium, magnesium, tellurium, tin, beryllium, and manganese benefit stress-corrosion resistance under some circumstances, but not others. The other alloying additions tried had no large effect on stress-cracking resistance. None of the elements added accelerated stress cracking. The impurities in commercial brass are not responsible for season cracking.

Jan 1, 1945

By William Priestley

The author has shown, by .practical experiments, how the rate of cooling steel in the mold governs ingotism, segregation, the formation of dendrites, and the distribution of intergranular material; and the resulting effect these conditions have on the physical qualities of the steel before annealing, after annealing, and after forging. The paper also describes how the structure of steel is affected by the design of the mold and the method of pouring. It is shown that the various constituents of carbon steel segregate differently under different rates of cooling. For the classes of steel covered in this paper, it is concluded that the best physical structure and the most uniform chemical composition is obtained by pouring the steel at a low temperature and solidifying as rapidly as possible in the mold. MUCH time has been devoted, by metallurgists, to the study of steel after solidification and remarkable strides have been made in the heat treatment of steel, but less knowledge is available of the thermophysical, activity of the constituents of steel prior to solidification in the mold. It is known that certain elements added to steel produce marked changes in physical properties, also that other elements added to steel produce similar changes, but we have only meager knowledge as to how these elements combine in steel under different conditions of solidification. It is not sufficient to know, from chemical analysis, that a certain element is present in steel. We should know how this element is in combination with the other elements and whether the combination is such as will give the greatest physical properties. Certain elements go into solid solution with the iron, while others segregate to the grain boundaries and combine with the impurities collected there. Until it is known where an alloy produces the most beneficial effect and a means, is determined for controlling its physical location by altering solidification conditions, or otherwise, we will not obtain the maximum value from our alloys.

Jan 2, 1924

By Inn-Joon Park

Major problems associated predicting soil-structure interaction behavior are based on the fact that soil is neither homogeneous nor elastic and soil properties are spatially variable. There also exist significant coupling problems between the behavior of the structure and geologic media. When designing foundation or other geotechnical structures, the load transfer between the soil and structure takes place at the contact surface. This surface is called the interface. The behaviors of interface play an important role in the load-deformation response of soil-structure interaction systems. The purpose of this study is to develop improved model for simulation of saturated sand-steel pile interface behavior based on a general concept, called the disturbed state concept (DSC), which can characterize the behavior of saturated soils under dynamic loads. In this study, the Disturbed State Concept (DSC) constitutive model is calibrated and modified for steel pile-saturated sand interface and interaction by using the continuous hardening model for relative intact (Rl) state and the critical state model for the fully adjusted (FA) part in the saturated sand material. The general formulation for implementation has been developed. Then, the DSC model with modification for interface and saturated sand is implemented in finite element program based on the generalized Biot's theory. The interface tests under one-way monotonic and two-way cyclic loading and cyclic triaxial tests are executed for defining the parameters for interface and surrounding soils. Based on these parameters, steel pile-saturated sand interface and interaction are numerically simulated using the finite element program modified in this study. The DSC predictions show improved agreement with the observed results from laboratory test.

Jan 1, 2002

By J. M. Wempen, M. K. McCarter

"Differential Interferometric Synthetic Aperture Radar (DInSAR) is a satellite-based remote sensing technique capable of measuring centimeter-level surface displacement with high spatial resolution over large areas. Regular monitoring of subsidence due to underground mine development is one potential application of DInSAR, and in this study, the application of DInSAR for subsidence monitoring is evaluated for two mining regions in the mountain west of the United States. In general, DInSAR has potential to identify the shape and extent of subsidence; in some cases, magnitudes and rates of subsidence can be defined. Importantly, the effectiveness of DInSAR for subsidence monitoring depends on the radar band (wavelength), the subsidence rate and the time between image acquisitions, and the topographic and vegetative surface characteristics. INTRODUCTION Differential Interferometric Synthetic Aperture Radar (DInSAR) is a satellite-based remote technique that can be used to measure small surface displacements. Under good conditions, centimeter-level displacements can be measured with subcentimeter accuracy (Buckley, 2000; Massonnet and Feigl, 1998). Additionally, DInSAR data have relatively high spatial and temporal resolutions. Pixels in Synthetic Aperture Radar (SAR) images can have a ground resolution as small as about 3 m, and images often include tens to hundreds of thousands of pixels and cover tens of kilometers. Regions are imaged regularly, and periods between images typically range from weeks to months. In DInSAR, phase measurements from two radar images acquired over the same region at different times are used to precisely measure relative distances (Rosen, 2014). Surface deformation, topography, and changes in the satellite position all contribute to differences in the length of the path that the radar wave travels in each image. SAR sensors use radar with relatively long wavelengths; L-band (24 cm wavelength), C-band (6 cm wavelength), and X-band (3 cm wavelength) radar are used most commonly. Because the wavelengths are long, small changes in the path length of the radar signal can be quantified by measuring the change in the phase of the radar signal between the images. In general, changes in the path length due to changes in the satellite position and topography are known or can be estimated, and centimeter-level changes in the path length due to deformation are measurable. This study evaluates the effectiveness of DInSAR for measuring subsidence in two mining regions in the mountain west of the United States. L-band data from the Advanced Land Observing Satellite (ALOS) and X-band data from the TerraSAR-X mission are evaluated. Imaging characteristics, including the radar band and the time between image acquisitions, are important for effective subsidence monitoring."

Jan 1, 2017